ICAME2003
ICAME2003
Proceedings of the 27th International Conference on the Applications of the Mossbauer Effect (ICAME 2003)
held in Muscat, Oman, 21-25 September 2003
Edited by
A. A. YOUSIF
A. D. AL RAWAS
and
Sultan Qaboos University, Muscat, Oman
Reprinted from Hyperjine Interactions Volume 156, Nos. 1-4 (2004) Volume 157, Nos. 1-4 (2004)
SPRINGER SCIENCE+BUSINESS MEDIA, B.V.
A c.I.P. Catalogue record for this book is available from the Library of Congress.
ISBN 978-90-481-6726-5 ISBN 978-1-4020-2852-6 (eBook) DOI 10.1007/978-1-4020-2852-6
Printed on acid-free paper
All Rights Reserved © 2004 Springer Science+ Business Media Dordrecht Originally published by Kluwer Academic Publishers in 2004 Softcover reprint of the hardcover 1st edition 2004 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner.
Table of Contents
Advances in Experimentation, Theory and Methodology
A. L. KHOLMETSKII, V. A. EVDOKIMOV, M. MASHLAN, O. V. MI­ SEVICH and A. R. LOPATIK / Mossbauer Instrument Package
1-2
MS-2000IP 3-8
A. L. KHOLMETSKII, W. POTZEL, R. ROHLSBERGER, U. VAN BURCK and E. GERDAU / Nuclear Resonant Scattering of Synchrotron Radi­ ation as a Method for Distinction between Covariant Ether Theories and Special Relativity 9-13
M. MASHLAN, V. YEVDOKIMOV, J. PECHOUSEK, R. ZBORIL and A. KHOLMETSKII / Mossbauer Spectrometer with Novel Moving System and Resonant Detection of Gamma Rays
K. SZYMANSKI, D. SATULA and L. DOBRZYNSKI / Angular Distribution of Hyperfine Magnetic Field in Fe304 and Fe66Ni34 from Mossbauer Polarimetry
YU. MALTSEV, S. MALTSEV, M. MENZEL, B. ROGOZEV and A. SIL­ VESTROV / Two-Dimensional Mossbauer Spectra
Amorphous and Nanophase Materials, Small Particles
D.-S. XUE and F.-S. LI / 57Fe Mossbauer Study of Magnetic Nanowires
D.-S. XUE, L.-Y. ZHANG and F.-S. LI / Synthesis and Mossbauer Study of Maghemite Nanowire Arrays
T. FURUBAYASHI / Mossbauer Characterization of Iron-Based Nanogranular Films
N. S. GAJBHIYE, R. S. NINGTHOUJAM and J. WEISSMULLER / Moss­ bauer Study of Nanocrystalline E-Fe3-xCoxN System
N. S. GAJBHIYE, G. BALAJI, S. BHATTACHARYYA and M. GHAFARI/ Mossbauer Studies of Nanosize CUFe204 Particles
J. GHOSE, K. S. K. VARADWAJ and D. DAS / Mossbauer Studies on Nano­ crystalline Diol Capped y-Fe203
J. RESTREPO and J. M. GRENECHE / Hyperfine and Structural Properties of the Mechanically Alloyed (FeMnhoCu7o System
Y. KOBAYASHI, S. KIAO, M. SETO, H. TAKATANI, M. NAKANISHI and R. OSHIMA / 197 Au Mossbauer Study of Bimetallic Nanoparticles Prepared by Sonochemical Technique
15-19
21-26
27-30
31-40
41-46
47-50
51-56
57-61
63-67
69-73
75-79
O. SCHNEEWEISS, N. PIZUROvA, Y. JIRAsKovA, T. ZAK, P. BEZDICKA and H. REUTHER / Phase Composition and Properties of Iron Nanocrystals and Clusters Embedded in MgO Matrix 81-87
S. J. STEWART, R. C. MERCADER, G. PUNTE, J. DESIMONI, G. CERNIC- CHIARO and R. B. SCORZELLI / Shifting the Superparamagnetic Limit of Nanosized Copper Iron Spinel 89-95
S. SINGHAL, A. N. GARG and K. CHANDRA / Synthesis of Nanocrystalline Nio.5Zno.5Fe204 by Aerosol Route and Its Characterization 97-102
Applications in Physics, Including Magnetism and Lattice Dynamics
P. BONVILLE, J. A. HODGES, E. BERTIN, J.-PH. BOUCHAUD, P. DAL­ MAS DE REOTIER, L.-P. REGNAULT, H. M. R0NNOW, J.-P. SANCHEZ, S. SOSIN and A. YAOUANC / Transitions and Spin Dynamics at Very Low Temperature in the Pyrochlores Yb2Ti207 and Gd2Sn207 103-111
S. J. KIM, K.-D. JUNG and C. S. KIM / Mossbauer and Neutron Diffraction Studies on Co-AI Ferrite 113-122
I. A. AL-OMARI, A. GISMELSEED, A. RAIS, H. M. WIDATALLAH, A. AL RAWAS, M. ELZAIN and A. A. YOUSIF / Mossbauer Studies of Feo.7-xSio.3Mnx Alloys
K. BHARUTH-RAM, J. E. BUTLER, D. NAIDOO and G. KLINGELHOFER / Observation of Substitutional Fe in CEMS Measurements on Syn-
123-127
B. BRZESKA-MICHALAK and A. OSTRASZ / Interaction between In- terstitial Hydrogen and Fe Atoms within the f3-Hydride Phase in Nbl-yFeyHx Alloys 137-142
G. LI, T. AKITSU, O. SATO and Y. EINAGA / First Observation of Photoin­ duced Magnetization for the Cyano-Bridged 3d-4f Heterobimetallic Assembly Nd(DMFMH20h(JL-CN)Fe(CN)s·H20 (DMF = N,N- Dimethylformamide) 143-149
T. ERICSSON, Y. A. ABDU, H. ANNERSTEN and P. NORDBLAD / Non- Magnetic Stainless Steels Reinvestigated - a Small Effective Field Component in External Magnetic Fields 151-155
L. A. BAUM, S. J. STEWART, R. C. MERCADER and J. M. GRENECHE / Magnetic Response and Hyperfine Magnetic Fields at Fe Sites of Sr3Fe2M09 (M = Mo, Te, W, U) Double-Perovskites 157-163
M. T. JEONG / Modification of Nuclear Decay Constant in the Finite Space 165-168
J. S. KUM, S. J. KIM, I. B. SHIM and C. S. KIM / Mossbauer Studies and Magnetic Properties of Y 3-xCexFe5012 169-174
N. KOJIMA, Y. ONO, Y. KOBAYASHI and M. SETO I Control of Charge Transfer Phase Transition in Iron Mixed-Valence System (n-CnH2n+ 1)4 N[FeIIFellI(dtohl (n = 3-6; dto = C202S2) 175-179
A-F. LEHLOOH, S. MAHMOOD, M. MOZAFFARI and J. AMIGHIAN I Mossbauer Spectroscopy Study on the Effect of AI-Cr Co-Substitution in Yttrium and yttrium-Gadolinium Iron Garnets 181-185
A. GRUSKOVA, J. LIPKA, M. PAPANOVA, D. KEVICKA, A GONZA­ LEZ, G. MENDOZA, I. TOTH and J. SLAMA I Mossbauer Study of Microstructure and Magnetic Properties (Co, Ni)-Zr Substituted Ba Ferrite Particles 187-194
I. NOWIK and I. FELNER I Mossbauer Studies of Dilute 119Sn and 57Fe in SrRu03 and Sr2FeRu06
O. YU. PANKRATOVA, A V. ZABOLOTNAYA, K. A HISTIAEV, V. V. PAN­ CHUCK, V. G. SEMENOV, R. A ZVINCHUK and A V. SUVOROV I
195-200
Mossbauer Studies on the Quasibinary System FeTe1.45-TiTe1.45 201-204
M. ELZAIN, A AL RAWAS, A YOUSIF, A GISMELSEED, A RAIS, I. AL-OMARI, K. BOUZIANE and H. WIDATALLAH I Magnetic Properties of Iron Clusters in Silver 205-212
A YOUSIF, K. BOUZIANE, M. E. ELZAIN, X. REN, F. J. BERRY, H. M. WI­ DATALLAH, A AL RAWAS, A GISMELSEED and I. A AL­ OMARI I Magnetic Properties of Nanocrystalline FexCul-x Alloys Prepared by Ball Milling 213-221
H. M. WIDATALLAH, A M. GISMELSEED, K. BOUZIANE, F. J. BERRY, A D. AL-RAWAS, I. A AL-OMARI, A A YOUSIF and M. E. ELZAIN I The Formation of Lithiated Ti-Doped a-Fe203 Nanocrystalline Particles by Mechanical Milling of Ti-Doped Lithium Spinel Ferrite 223-228
A. RAIS, A A YOUSIF, A GISMELSEED, M. E. ELZAIN, A AL RAWAS and I. A AL-OMARI I Effect of Mg2+ on the Magnetic Compensa- tion of Lithium-Chromium Ferrite 229-234
T. SUENAGA, S. NASU, T. KAWAKAMI and R. H. HERBER I High­ Pressure 57Fe Mossbauer Spectroscopy of Octamethyl-Ethynyl- Ferrocene 235-240
T. SEGI, S. NASU, S. MORIMOTO and H. TOKORO I 57Fe Mossbauer Spectroscopic Study of Fe-B Compounds
Biological and Medical Applications
V. SCHUNEMANN, C. JUNG, F. LENDZIAN, A-L. BARRA, T. TESCHNER and A X. TRAUTWEIN I Mossbauer- and EPR-Snapshots of an
241-245
Enzymatic Reaction: The Cytochrome P450 Reaction Cycle 247-256
M. MIKHAYLOVA, Y. S. JO, D. K. KIM, N. BOBRYSHEVA, Y. ANDER­ SSON, T. ERIKSSON, M. OSMOLOWSKY, V. SEMENOV and M. MUHAMMED / The Effect of Biocompatible Coating Layers on Magnetic Properties of Superparamagnetic Iron Oxide Nanoparticles 257-263
T. OHYA, J. TAKEDA and M. SATO / Spin States of Iron(III) in Highly Saddled Dodecaphenylporphyrin Complexes 265-272
M. I. OSHTRAKH, O. B. MILDER and V. A. SEMIONKIN / Mossbauer Spectroscopy of Iron Containing Vitamins and Dietary Supplements 273-277
M. I. OSHTRAKH, O. B. MILDER, V. A. SEMIONKIN, P. G. PROKOPENKO and L. I. MALAKHEEVA / Comparative Study of Human Liver Ferritin and Chicken Liver by Mossbauer Spectroscopy. Preliminary R~~ m~M
T. TESCHNER, A. X. TRAUTWEIN, V. SCHUNEMANN, L. A. YAT­ SUNYK and F. A. WALKER / Low-Spin Ferriheme Models of the Cytochromes: Correlation of Molecular Structure with EPR and Mossbauer Spectral Parameters 285-291
P. WEGNER, M. BEVER, V. SCHUNEMANN, A. X. TRAUTWEIN, C. SCHMIDT, H. BONISCH, M. GNIDA and W. MEYER­ KLAUCKE / Iron-Sulfur Proteins Investigated by EPR-, Mossbauer- and EXAFS-Spectroscopy 293-298
Chemical Applications, Structure and Bonding
M. ABDELMOULA, M. PETITJEAN, G. CABOCHE, J.-M. GENIN and L. C. DUFOUR / Mossbauer Study of Lanthanum-Strontium Ferro- manganite Oxides 299-303
F. J. BERRY, O. HELGASON and J. W. F. MOSSELMANS / Iron-57 Moss- bauer Spectroscopic Investigation of Manganese-Doped y-Fe203 305-309
K. IKEDA, N. KOJIMA, Y. ONO, Y. KOBAYASHI, M. SETO, X. J. LIU and Y. MORITOMO / Study on Chemical Bond and Electronic State of New Gold Mixed Valence Complexes CS2[AuIX2][AuIIIY4] (X, Y = CI, Br, I) by Means of 197 Au Mossbauer Spectroscopy 311-314
S. KAMALI, L. HAGGSTROM, S. RONNETEG and R. BERGER / Magnetic Properties of TIC02Se2 Studied by Mossbauer Spectroscopy 315-319
J. LINDEN, P. KAREN, H. YAMAUCHI and M. KARPPINEN / Exploring the Verwey-Type Transition in GdBaFe205+w Using 57Fe Mossbauer Spectroscopy 321-325
P. E. LIPPENS, J.-c. JUMAS and J. OLIVIER-FOURCADE / First Princi- ples Calculations of Mossbauer Spectra of Intermetallic Anodes for Lithium-Ion Batteries 327-333
F. J. BERRY, X. REN, J. R. GANCEDO and J. F. MARCO / 57Fe Mossbauer Spectroscopy Study of LaFel-xCox03 (x = 0 and 0.5) Formed by Mechanical Milling 335-340
T. M. MEAZ and C. BENDER KOCH / A Crystallographic and Mossbauer Spectroscopic Study of BaCoo.5xZnO.5x Tix Fe12-2x019 (M-Type Hexagonal Fenite) 341-346
H. MEHNER, M. MENZEL and M. NOFZ / Laboratory Intercomparison on the Determination of the Fe(II)/Fe(III) Ratio in Glass Using Mossbauer Spectroscopy 347-352
S. NAKASHIMA, Y. ASADA and T. OKUDA / 57Fe Mossbauer Spectroscopic Study on the Assembled Iron Complexes 353-358
M. TAKEDA, J. WANG, T. NISHIMURA, K. SUZUKI, T. KITAZAWA and M. TAKAHASHI / 155Gd Mossbauer Isomer Shifts and Quadrupole Coupling Constants of Gadolinium Complexes 359-364
L. STIEVANO, R. DELLA PERGOLA and F. E. WAGNER / Mossbauer Spec- troscopy in the Characterisation of Polymetallic Cluster Compounds: a Triple Mossbauer Study of (PPh4) [Fe2Ir2(CO) 12 {j.L3-Au(PPh3) }] 365-370
F. RENZ and P. KEREP / The Nonanuclear [Mo(IV){ (CN)Fe(III)(3-ethoxy- saldptn) }s]CI4 Complex Compound Exhibits Multiple Spin Transi- tions Observed by Mossbauer Spectroscopy 371-377
Earth Sciences, Mineralogy and Archaeology
O. HELGASON / Processes in Geophysics Studied by Mossbauer Spec- troscopy 379-388
Y. A. ABDU, H. ANNERSTEN, L. S. DUBROVINSKY and N. A. DUBRO­ VINSKAIA / High Pressure Mossbauer Studies on FCC Fe53Ni47 Alloy 389-394
M. FAJARDO, G. A. PEREZ ALCAzAR, A. M. MOREIRA and N. L. SPE­ ZIALI / Mossbauer and XRD Comparative Study of Host Rock and Iron Rich Mineral Samples from Paz del Rio Iron Ore Mineral Mine in Colombia 395-402
R. ZBORIL, M. MASHLAN, L. MACHALA, 1. WALLA, K. BARCOVA and P. MARTINEC / Characterization and Thermal Behaviour of Garnets from Almandine-Pyrope Series at 1200°C
N. I. CHISTYAKOVA, V. S. RUSAKOV, D. G. ZAVARZINA, A. I. SLO­ BODKIN and T. V. GOROHOVA / Mossbauer Study of Magnetite
403-410
Formation by Iron- and Sulfate-Reducing Bacteria 411-415
S. K. DEDUSHENKO, I. B. MAKHINA, A. A. MAR'IN, V. A. MUKHANOV and YU. D. PERFILIEV / What Oxidation State of Iron Determines the Amethyst Colour? 417-422
E. ENEROTH and C. BENDER KOCH / Fe-Hydroxysulphates from Bacterial Fe2+ Oxidation 423-429
A. KUNO, M. MATSUO, A. P. SOTO and K. TSUKAMOTO I Mossbauer Spectroscopic Study of a Mural Painting from Morgadal Grande, Mexico 431-437
H. REUTHER, T. ARNOLD and E. KRAWCZYK-BARSCH I Quantification of Secondary Fe-Phases Formed During Sorption Experiments on Chlorites 439-443
R. AISSA, C. RUBY, A. GEHIN, M. ABDELMOULA and J.-M. R. GENIN I Synthesis by Coprecipitation of AI-Substituted Hydroxysulphate Green Rust Fe~IFe~ty)AI~II(OHh2S04' nH20 445-451
R. RUFFLER, E. GJYLA<;I and K. NAGORNY I Mossbauer Study of Ancient Albanian Ceramics 453-458
M. Y. HASSAAN, F. M. EBRAHIM and S. H. SALAH I Variation of Some Physical Properties of Brownmillerite Doped with a Transition Metal Oxide 459-464
T. M. MEAZ, M. A. AMER and C. BENDER KOCH I Iron-Containing Adsorbents in Great Nile Sediments 465-469
Industrial Applications, Including Catalysis and Corrosion
J.-M. R. GENIN I Fe (II-III) Hydroxysalt Green Rusts; from Corrosion to Min- eralogy and Abiotic to Biotic Reactions by Mossbauer Spectroscopy 471-485
A. GISMELSEED, M. ELZAIN, A. YOUSIF, A. AL RAWAS, I. A. AL­ OMARI, H. WIDATALLAH and A. RAIS I Identification of Corro- sion Products Due to Seawater and Fresh Water 487-492
A. NAKANISHI and T. KOBAYASHI I Atmospheric Corrosion on Steel Studied by Conversion Electron Mossbauer Spectroscopy 493-496
L. ALDON, P. KUBIAK, A. PICARD, P. E. LIPPENS, J. OLIVIER-FOUR­ CADE and J.-C. JUMAS I Mossbauer Spectrometry as a Powerful Tool to Study Lithium Reactivity Mechanisms for Battery Electrode Materials 497-503
Material Science and Metallurgy
J. DESIMONI I Arrangements of Interstitial Atoms in fcc Fe-C and Fe-N Solid Solutions 505-521
J. CHOJCAN I A Dilute-Limit Heat of Solution of 3d Transition Metals in Iron Studied with 57Fe Mossbauer Spectroscopy 523-529
L. VERGARA, J. DESIMONI, A. FERNANDEZ GUILLERMET and G. J. ZARRAGOICOECHEA I Distribution of N Atoms in the fcc Fe-N Interstitial Solid Solution 531-539
M. MIZRAHI, A F. CABRERA, S. M. COTES, S. J. STEWART, R. C. MER­ CADER and J. DESIMONI / Distribution of Mn Atoms in a Substi­ tutional bcc-FeMn Solid Solution
M. M. EL-DESOKY, A AL-HAJRY, M. TOKUNAGA, T. NISHIDA and M. Y. HASSAAN / Effect of Sulfur Addition on the Redox State of
541-545
Iron in Iron Phosphate Glasses 547-553
C. M. IONICA, L. ALDON, P. E. LIPPENS, F. MORA TO, J. OLIVIER­ FOURCADE and J.-C. JUMAS / Structural and Electronic Features of Sb-Based Electrode Materials: 121 Sb Mossbauer Spectrometry 555-561
N. LAKSHMI, K. VENUGOPALAN and V. K. AGARWAL / Study of Disordered Fe2Cr(l_x)MnxAl Alloys 563-567
D. OYOLA LOZANO, Y. R. MARTINEZ, H. BUSTOS and G. A PEREZ ALCAzAR / Mossbauer and X-ray Study of Fel-xAlx, 0.2 :;:; x :;:; 0.5, Samples Produced by Mechanical Alloying 569-574
H. REUTHER, E. RICHTER, F. PROKERT, M. VEDA, A F. BELOTO and G. F. GOMES / Investigation of Steel Surfaces Treated by a Hybrid Ion Implantation Technique 575-579
Surfaces, Interfaces, Thin Films and Multilayers
M. CARBUCICCHIO and M. RATEO / Ferromagnetic Planar Nanocompos- ites 581-593
M. A ANDREEVA / Surface and Interface Investigations by Nuclear Resonant Scattering with Standing Waves 595-606
M. A. ANDREEVA, L. HAGGSTROM, B. LINDGREN, B. KALSKA, A-M. BLIXT, S. KAMALI, O. LEUPOLD and R. RUFFER / Nuclear Resonant Reflectivity Investigations of a Thin Magnetic 57Fe Layer Adjacent to a Superconducting V Layer 607-613
J. JURASZEK, J. TEILLET, A FNIDIKI and M. TOULEMONDE / CEMS Investigations of Swift Heavy Ion Irradiation Effects in Tb/Fe Multi- layers 615-621
K. K. KADYRZHANOV, V. S. RUSAKOV, B. O. KORSHIYEV, T. E. TURKE- BAEV and M. F. VERESCHAK / Thermally Induced Processes of Intermetalloid Phase Formation in Laminar Systems Fe-Sn 623-628
K. NOMURA, K. TAKAHASHI, M. TAKEDA, K. SHIMIZU, H. HABASAKI and E. KUZMANN / DCEMS Study of Thin Oxide Layers and In­ terface of Stainless Steel Films Deposited by Sputtering Austenitic AISI304 629-636
K. NOMURA and Y. YAMADA / CEMS Study on Fe Films Deposited by Laser Ablation 637-641
v. V. PANCHUCK, V. G. SEMENOV and V. M. UZDIN / The Investigation of the Magnetic Properties of Metallic Multilayers by Angle Dependent Mossbauer Spectroscopy 643-647
J. R. GANCEDO / Concluding Remarks 649-651
Author Index 653-656
Preface
These are the proceedings of the 27th International Conference on the Applications of the Mossbauer Effect (ICAME 2003), which was held in Muscat (Oman) during the period 21-25 September 2003. The Iraq war, which took place a few months earlier, shadowed the conference organization during the preparation stages and raised many doubts over its realization. However, the forceful determination and commitment of the faithful participants encouraged the Organizing Committee to carry on. We were pleased of the number of participants that exceeded our expec­ tations. In particular the conference was honored by the participation of Rudolf Mossbauer himself.
The proceedings are divided into nine sections according to the conference top­ ics. All papers were reviewed by at least two referees. Out of the thirteen invited talks presented at the conference, nine were submitted for publication. Each topic section starts with the theme's invited talks wherever available. This is followed by the accepted contributions in alphabetical order of the corresponding author. Contributions, for which the abstracts were received late, are placed towards the end of the relevant section.
A number of people contributed to the realization of these proceedings. Amthauer G., Becker K.D., Bill E., Bonville P., Carbucicchio M., Gancedo R, Greneche J.-M., Genin J.-M., Herber R, Music G., Rueffer R, Pankhurst Q., Sanchez F. and Trautwein A.x., who were selected by the Program Committee as topic coordinators, reviewed and classified the abstracts for presentation at the conference. Following the conference Amthauer G., Bill E., Bonville P., Carbucic­ chio M., Gancedo R, Greneche J.-M., Genin J.-M., Sanchez F. and Trautwein A.X. helped in the selection of referees to the submitted articles. We very much ap­ preciate the great help extended by the topic coordinators who also tolerated our various and persistent queries and requests. In addition, we would like to thank Guido Langouche, who provided us with additional names whenever we ran short of referees and for his support as the Editor-in-chief of Hyperfme Interactions.
The ICAME 2003 was the first major event organized by the Department of Physics. Its staff and students worked in a well-coordinated and cooperative man­ ner, which resulted in a conference that was well praised, in writing, by many participants. The staff of the Public Relation Department at Sultan Qaboos Uni­ versity worked around the clock to ease and facilitate the arrival and departure of all participants. We would like to acknowledge the great contributions of both departments.
2 PREFACE
Finally we would like to thank Sultan Qaboos University, UNESCO and IS­ ESCO for their generous financial contributions.
Mohamed Elzain Ali Yousif
• Hyperfine Interactions 156/157: 3-8, 2004. © 2004 Kluwer Academic Publishers.
Mossbauer Instrument Package MS-2000IP
O. V. MISEVICH2 and A. R. LOPATIK2
1 Department of Physics, Belarus State University, 4, F. Skorina Ave., 220080 Minsk, Belarus 2Institute of Nuclear Problems, Belarus State University, 11, Bobruiskaya Str., 220050 Minsk, Belarus 3 Faculty of Experimental Physics, Palacky University, Svobody 26, 77146 Olomouc, Czech Republic
3
Abstract. The paper describes the Instrument Package MS-200OIP, which is based on some new technical ideas of the authors. It allows to increase essentially the productivity of Mossbauer mea­ surements in transmission Mossbauer spectroscopy, in conversion X-ray Mossbauer spectroscopy (XMS), as well as in conversion electron Mossbauer spectroscopy (CEMS).
Key words: transmission Mossbauer spectroscopy, conversion X-ray Mossbauer spectroscopy, con­ version electron Mossbauer spectroscopy.
1. General description
The instrument package has been developed on the basis of the personal Mossbauer spectrometer MS-2000 [1]. It contains three spectrometric sections with a common operational module, connected with PC. The first section is based on fast YAP (yttrium aluminum perovskite) scintillation detector in transmission measuring geometry. The second section contains a proportional detector for registration of characteristic iron X-ray radiation in scattering geometry (XMS), while the third section is unitized for CEMS with an air scintillation detector for low-energy elec­ trons. The system of modulation of the energy of resonant gamma-quanta is also common for all sections, and it is based on a mini Doppler modulator [2] with standard feed-back system. Driving system provides an integral non-linearity of the velocity scale less than 0.1 %, and the velocity resolution for sodium nitroprusside standard sample is better than 0.24 mmls. The control system of MS-2000IP allows to choose a velocity form (constant acceleration, constant velocity), velocity range (±100 mmls), acquisition time, and spectrum name for spectra archiving. The MS- 2000IP also contains a section for amplitude analysis on the basis of single channel analyzer with a fixed window and variable position. Data acquisition is realized by PIGGY 321154/320 microcomputer. Mossbauer spectra of 2048 channels are accu­ mulated in the constant velocity or constant acceleration mode. The main service program is written by the Lab VIEW graphical programming language and has a form of a virtual instrument [3].
4 A. L. KHOLMETSKll ET AL.
2. Section for high-performance transmission Mossbauer spectroscopy
In our earlier papers [4, 5] we have shown that the productivity of transmission Mossbauer measurements Q, defined as a ratio of a number of accumulated spectra with a fixed statistic error to the total measuring time, is proportional to
(1)
where h is the limited count-rate of detector, while Ss is the spectrometric selec­ tivity of the detector. The limited count-rate is inversely proportional to a duration of output pulse of the detector. The factor of proportionality is usually taken as 1/10 for random events [6]. The parameter Ss is defined as a ratio of total count­ rate in a selected energy window to the count-rate of resonant events. Equation (1) was used by us in a search of optimal combination of characteristics of detectors in transmission measurements, proceeding from two conclusions:
if Ss essentially exceeds a unit, than its further increase is not accompanied by essential increase of the productivity Q;
the productivity Q linearly increases with increase of h.
Analysis of conventional detectors for Mossbauer spectroscopy according to Equation (1) reveals incorrectness of traditional approach to a choice of gamma­ detectors, when the attention was firstly focused on their energy resolution, without taking into account the value of h. In order to increase the productivity of trans­ mission Mossbauer measurements, it is necessary to create such a detector, which has extremely high admissible count-rate h and the value of Ss > 1. An optimal combination of these requirements was realized in scintillation detector YAI03:Ce (yttrium aluminum perovskite, YAP). Such a detector has a conversion efficiency about 40% in comparison with NaI(TI). Therefore, its energy resolution is about 30% worse than for NaI(TI). It leads to some decrease of Ss. However, this pa­ rameter does not play an essential role in productivity of transmission Mossbauer measurements. At the same time, the decay time of YAP is one order of magnitude smaller than for NaI(Tl). This circumstance opens a possibility to enlarger the admissible count-rate of YAP detector. Simultaneously one can choose an optimal thickness of scintillator, which provides almost 100% registration efficiency for 14.4 resonant gamma-quanta with very small registration efficiency for background radiation 122 keY + 136 keY. Under these conditions the fast detector YAP allows to reduce the time of Mossbauer spectra acquisition approximately 6-9 times in comparison with the traditional detectors [4,5, 7].
The spectrometric section for transmission Mossbauer measurements represents a separate mechanical unit, which includes the Doppler modulator, detector YAP, sample holder and collimating system. The unit contains a double protection from external mechanical vibrations (Figure 1).
MOSSBAUER INSTRUMENT PACKAGE MS-2000IP 5
Figure 1. Spectrometric section, having a form of tube, is connected with the basic electronic module of MS-2000IP (Mossbauer spectrometer MS-2000).
3. Section for registration of conversion X-ray radiation in back-scattering geometry for XMS
In scattering geometry a detector of radiation is placed outside a direct gamma­ beam, that drops a requirement to a high admissible count-rate. In such a case a productivity of measurements is fully determined by the effect-background ratio, which depends on the energy resolution of detector. Due to this reason the fast scintillation detectors with comparably law energy resolution lose their advantages in favor of proportional and semiconductor detectors with high resolution. For registration of characteristic iron X-ray radiation with the energy 6.3 keY we use a xenon proportional counter CHIP, which has a registration efficiency about 100% and the relative energy resolution less than 15%.
Registration section for conversion X-ray radiation represents a separate me­ chanical unit, which contains a Doppler modulator, proportional counter with shielding, sample holder, collimating system and protective shield. Its view is shown in Figure 2.
4. Section for registration of conversion and Auger electrons for CEMS
It is well known that different kinds of gas detectors with registration of pulses of current are widely-spread detectors for the low energy electrons in CEMS. We suggested and developed a gas detector with registration of pulses of light, accom­ panying the discharge processes in working gas [8]. Such a method of registration has a number of advantages in comparison with traditional current method. The principal scheme of the developed detector is depicted in Figure 3.
6 A. L. KHOLMETSKII ET AL.
Figure 2. Section for XMS.
PM s
eM ollimator
He Figure 3. The scheme of air scintillation detector for CEMS.
The sample under investigation (S) is placed near the input window of the photomultiplier (PM). The sample is irradiated by a collimated tangential beam from the Mossbauer source MS. The S, PM and MS are placed in a hermetic chamber He. The sign of high-voltage on the sample (us) is opposite to the sign of high-voltage on the photocathode of PM.
The electrons leave the surface of the sample and cause the micro-discharges in the gap between S and PM. The value of the electric field in the gap is determined by the difference of the electric potentials of the sample and the photocathode of PM. A simplicity of the described construction of the detector is provided by the triple function of the PM: its photocathode is one of the electrodes, its glass bulb plays the role of the isolating film between the electrodes, and the PM properly detects the light pulses. We stress that the isolating film (glass of PM) between the electrodes prevents a development of micro-discharges into self-sustaining dis­ charge in working gas with non-controlled chemical composition. It allows one to use as working gas a natural air. It opens a possibility to conduct measurements with the samples of almost arbitrary form and size. We call the construction in Figure 3 as air scintillation detector (ASD).
MOSSBAUER INSTRUMENT PACKAGE MS-2000IP 7
Figure 4. Section for CEMS on the basis of air scintillation detector for low-energy electrons.
The selective properties of ASD to low-energy electrons follow from the inverse proportional dependence of the energy loses of electrons on their energy in the range of middle energies. Estimation of Ss for ASD was carried out by method of filter, and in optimal conditions Ss ~ 2 under almost 100% registration efficiency for low-energy electrons. In these conditions the value of the resonant effect for a Mossbauer spectrum of a natural sample a-Fe exceeds 10%.
We notice that in case of CEMS the tangential incidence of the gamma-beam on a surface of sample provides an increase of the count-rate by 1/ sin "6 times in com­ parison with the case of normal incidence of gamma-beam due to a corresponding increase of the path length of gamma-quanta in the surface layer referring to the maximum escape length of electrons. For chosen value of "6 = 5°, 1/ sin"6 ~ 10. Hence, the count-rate of the ASD is several times larger compared to normal in­ cidence used in standard CEMS detectors. In addition, the tangential incidence of gamma-beam on a surface of a sample makes the ASD directly sensitive to struc­ tural and magnetic anisotropy of the sample, that could be important for practical applications. A general view of the ASD for MS-2000IP is shown in Figure 4.
Currently the developed instrument package MS-2000IP is applied by us in transmission Mossbauer spectroscopy, as well as for investigation of surface layers of materials with involving CEMS and XMS.
References
1. Mashlan, M., Janchik, D., Mulaba, A. , Kholmetskii, A. L. and Pollak, H., Hyp. [nteract. 120-121 (1999),411. See also the website www.mossp.2000.com.
2. Evdokimov, V. A. , Fyodorov, A. A., Misevich, O. v., Mashlan, M., Kholmetskii , A. L. and Zak, D. , Nucl. [nstrum. Meth. B 95 (1995), 278.
3. Kholmetskii, A. L., Mashlan, M., J anchik, D., Zak, D., Dubka, F. and Snasel, v., In: M. Miglierini and D. Petridis (ed.), Mossbauer Spectroscopy in Material Science, Kluwer Academic Publisher, Dordrecht, 1999, p. 391.
4. Kholmetskii, A. L., Mashlan, M., Misevich, O. v., Chudakov, V. A., Lopatik, A. R. and Zak, D., Nucl. [nstrum. Meth. B 124 (1997), 143.
8 A. L. KHOLMETSKII ET AL.
5. Kholmetskii, A. L., Mashlan, M., Nomura, K., Misevich, O. V. and Lopatik, A. R., In: Current Advances in Materials and Processes, Vol. 13, The Iron and Steel Institute of Japan, 2000, p.1417.
6. Lyapidevskii, V. K., Metody Detektirovaniya Izluchenii, Atomizdat, Moscow, 1987, 514 p. (in Russian).
7. Mashlan, M., Jancik, D. and Kholmetskii, A. L., Hyp. Interact. 139 (2002), 673. 8. Kholmetskii, A. L., Mashlan, M., Misevich, O. V., Anashkevich, A. F., Chudakov, V. A. and
Guracevskii, V. L., NucZ. Instrum. Meth. B 124 (1997), 110.
Hyperfine Interactions 156/157: 9-13,2004. © 2004 Kluwer Academic Publishers.
Nuclear Resonant Scattering of Synchrotron Radiation as a Method for Distinction between Covariant Ether Theories and Special Relativity
9
A. L. KHOLMETSKII1, W. POTZEL2, R. ROHLSBERGER2, U. VAN BURCK2
and E. GERDAU3
I Department of Physics, Belarus State University, 4, F. Skorina Avenue, 220080 Minsk, Belarus 2 Physik-Department, Technische Universitiit Munchen, D-85747 Garching, Germany 3 Institut fur Experimentalphysik, Universitiit Hamburg, D-22761 Hamburg, Germany
Abstract. The paper stresses the importance for basic physics of the new proposed Champeney­ like rotor experiment with nuclear resonant scattering of synchrotron radiation. Such an experiment, being sensitive to energy shifts proportional to c-3 (c is the light velocity in vacuum), should be able to distinguish between predictions of special relativity theory and covariant ether theories, and thus allow to differentiate between them. The results of computer simulations of experiments with the 14.4 keY resonance in 57Fe show that an energy resolution /";,EjE at the level of 10- 16 can be expected which is enough to reveal the third order term.
Key words: Mossbauer effect, special theory of relativity, synchrotron radiation.
Experimental data obtained in high-energy physics and cosmic-ray physics dur­ ing the past decade again induced an exciting discussion about a possible violation of the Lorentz-invariance in Nature. In this connection some space-time theories with a covariant description of a hypothetical "absolute space" in the Universe (covariant ether theories, CETs) again attract great attention. The ideas of CETs go back to works by Lorentz and Poincare. However, for a long time, various CETs were considered as physically senseless formal mathematical constructions. The principal possibility of the existence of phenomena, where a hypothetical violation of Einstein's relativity principle might occur within the general relativity principle, was pointed out by Dirac [1]. The possible existence of such phenomena on a laboratory scale was substantiated and predicted in [2].
Let us briefly discuss some important characteristics of the Special Relativity Theory (SRT) and CETs. The SRT is based on two postulates: (a) All inertial ref­ erence frames (IRF) have equal rights, they are equivalent. The fundamental phys­ ical equations are the same (they are form-invariant) in inertial reference frames. (b) The velocity of light in vacuum c is a constant in all IRF. From these two postulates the Lorentz transformations follow in Minkowski space-time with its Galilean metrics. In particular, an "absolute" inertial frame, distinguished amongst all other inertial frames, does not exist. Lorentz transformations between two IRF
10 A. L. KHOLMETSKII ET AL.
are fully determined by their relative velocity. The principal characteristics of CETs are the following: (a) Space-time homogeneity, space-time isotropy, the causality principle as well as the general relativity principles (covariance of fundamental physical equations for admissible space-time transformations) are all valid [2, 3]. (b) An "absolute" inertial frame Ko is allowed to exist. Therefore the postulates of SRT mentioned above are violated. (c) An "absolute" inertial frame Ko, if it exists, is unique. In Ko the geometry of space-time is pseudo-Euclidean with Galilean metrics. In any other IRF moving at a constant "absolute" velocity, the metrics of physical space-time is oblique-angled [3]. True (physical) values differ, in general, from their magnitudes measured in experiment.
As a general consequence of these principles, two theorems of CETs follow [3]: (1) A transformation of measured space and time intervals from Ko to any arbitrary IRF K has a Lorentzian form. (2) Lorentz transformations between two inertial frames K1(Xi) and K 2(x;') always have to proceed via the absolute frame Ko(x;), where Xi, x;, and x;' are experimentally measured space-time four-vectors. There­ fore in CETs, Nature does not "know" a direct relative velocity between two inertial frames Kl and K2• Nature only "operates" with absolute velocities, being applied in the Lorentz transformations. A very important consequence of this transforma­ tion rule via the absolute frame is the appearance of a frequency (energy) shift between emitter and receiver of electromagnetic radiation, which is proportional to the "absolute" velocity of the Earth [3, 4]. Such a shift appears, e.g., when source and receiver rotate at different distances from a common rotational axis. The shift is proportional to c-3:
(1)
(u is the linear velocity at the perimeter of the rotor and v is the absolute velocity of the Earth). Although such a possible violation of Einstein's relativity principle represents a tiny effect, it nevertheless can be detected by the modem technique of nuclear resonant scattering of synchrotron radiation. In Ref. [4] we considered a possible experiment with resonant radiation of 67Zn, which, however, faces large experimental difficulties. In this paper we propose an experimental scheme involv­ ing the 57Fe resonance, where a high sensitivity is reached due to the application of the recently discovered Nuclear Lighthouse effect [5]. The principal setup, to be realized at an undulator beamline of a third-generation synchrotron radiation source like the ESRF, is shown in Figure 1.
The high-speed rotor carries two targets: the inner target close to the central axis of the rotor and the outer target covering the circumference of the rotor. Both targets are made from metal foils containing the Mossbauer isotope 57Fe with the transition energy of 14.4 ke V. After monochromatization to a few me V around the nuclear transition energy achieved by Bragg reflections in Si channel-cut stages, the synchrotron radiation pulse of typically several 100 ps in length excites the nuclei in both targets. This excitation of the nuclei is phased in time by the SR pulse and extends over both spatially separated targets. Such a collective nuclear excitation
NRS OF SYNCHROTRON RADIATION 11
rotor slit I
8~ slit 2
~, ,-----------' :: detectors 1 cm 15 m
Figure 1. Schematic layout of an experiment at an undulator beamline, e.g., at the ESRF. CRL denotes a compound refractive lens, and HRM a high-resolution monochromator.
(nuclear exciton) follows the rotation of the rotor. This gives rise to the Nuclear Lighthouse Effect because the direction of spatially coherent forward reemission is rotated together with the target. As a result, the time evolution of the nuclear decay is mapped to an angular scale and can be recorded with a position sensitive detector [6]. One can show that background radiation arising from small-angle X­ ray scattering (SAXS) from the rotor and the sample itself can be significantly reduced by the use of single-crystalline materials like Al20 3 (sapphire) [6]. An additional effect for background reduction relies on the spatial displacement of the nuclear exciton during its lifetime. Due to the motion of the exciton, the radiation sources of the small-angle scattering and the delayed resonant radiation are spa­ tially separated. This allows one to apply a system of slits to almost fully suppress SAXS from the rotor and the sample. In order to avoid SAXS in air, the rotor has to be operated in vacuum.
Due to the energy difference (1), to which the conventional second order Dopp­ ler shift (SOD), b.Esoo/ E = u2/2c2, has to be added, the radiation from both targets recorded in the detector shows a characteristic Quantum Beat (QB) inter­ ference pattern. The QB has the period T = h/ b.E, where h is Planck's constant. In the absence of the effect predicted by CETs, the SOD gives a QB with the period
h Tsoo = --­
b.Esoo (2)
If the CETs effect is present, as it follows from Equation (1), the T should vary between the extremal values [4]:
TJ = h/(! + v/2c)b.Esoo, and T2 = h/(1 - v/2c)b.Esoo. (3)
Therefore,
c b.Esoo c (4)
where the average period Tav is given by Equation (2). If the observation window rob of the experiment is much larger than Tav, the number n of QB maxima within rob will be
rob n~-.
Tav (5)
LlESOD = 0.15 mmls
1....-...1...---'----'-----'_-'----'--------'----' 10-11 "--...1...---'----'-----'_-'----'--------'---"
880
Figure 2. The top graph displays the time spectrum of nuclear resonant forward scattering from two 100 nm thick a-Fe foils with a difference in SOD of 0.15 mm1s. The lower figures display the time ranges around the first two minima of the SOD. It was assumed that CET is valid and introduces the extremal modulation periods of =0.1499 mm1s (solid line) and =0.1501 mm1s (dashed line).
Then the time difference for n QB maxima between the two extremal periods is given by
(6)
Here and in the further analysis we assume the velocities u = 300 rnIs and v = 300 km/s (a typical value for Galaxy objects relative to the cosmic microwave background radiation). An observation window of Tob = 1500 ns has been chosen corresponding to about 10 times the nuclear lifetime Ts of the Mossbauer level (Ts ~ 141 ns). Then we obtain Tav = 575 ns, i.e. there are about three maxima within Tob, and !:l.T ~ 1.5 ns. Using fast modem electronics such a value for LlT can be expected to be observable.
A high sensitivity for the measurement of small energy shifts can be achieved when the time response from the foils is additionally modulated by a fast quantum beat pattern. The basic idea is to analyze the structure of the beat pattern in the minima of the SOD oscillations, as well as the shift of the minima. We will explain these features for the case of ferromagnetic Fe metal with an internal hyperfine field of 33.3 T at room temperature. If magnetized perpendicular to the storage ring plane, only the !:l.m = 0 transitions are excited, leading to a quantum beat period of 9.5 ns. Figure 2 displays the results of a calculation for an average SOD of 0.15 mrnIs (u = 300 rnIs), that would be modulated between values of 0.1499 mrnIs
NRS OF SYNCHROTRON RADIATION 13
and 0.1501 mmls ifCETwere valid. The samples are two iron foils with a thickness of 100 nm each, highly enriched in 57Fe. The calculations show that significant effects can be observed already at early times. Simultaneously it proves the high sensitivity of this method. In particular, the expected relative energy resolution obtained from the calculations of Figure 2 will be better than 10-16 . This will be sufficient for a reliable measurement of the effects predicted by CETs.
Concerning the experiment itself, the incident synchrotron radiation beam is fo­ cused to the rotor position by a CRL (compound refractive lens) to a vertical beam height of less than 50 /Lm. The radiation is monochromatized by a HRM (high­ resolution monochromator) to a bandwidth of 6.5 meV to reduce the non-resonant background. As indicated in Figure 1, the rotor spins around a horizontal axis with a frequency of 1600 Hz. The detector is located at a distance of approximately 15 m from the rotor, where the resonant radiation is deflected by about 150 mm off the primary beam. The time window of 50 ns around the first QB minimum due to the SOD is selected by a 7.5 mm wide slit. An array of avalanche photodiodes (APDs) covers this time range to monitor the intensity around this minimum. APDs are proposed here because of their very low background noise. However, an ideal detector would be a position sensitive detector with a spatial resolution of about 50 /Lm and a very low background noise.
Finally, we want to give a rough estimate of the count-rate in such an experi­ ment. The integrated intensity over the time range from 832 ns to 860 ns in Figure 2 amounts to that within an energy range of about 2 x 10-6 roo This sets a limit for the observable effect. For this reason, the experiment has to be performed at one of the strongest X-ray sources available, like the European Synchrotron Radia­ tion Facility ESRF (Grenoble, France). The best high-resolution monochromator available at beamline !DI8 delivers a flux of almost 8 x 109 S-I within a band of 6.4 meV, which corresponds to 6000/(s·ro) with ro = 4.7 neY. With this intensity, one arrives at approximately 130 counts during a 3-hour period falling into the time range mentioned above. Considering the flux available at present third-generation synchrotron radiation facilities, to be sensitive to an effect of !1E / E ~ 3 X 10-16
as predicted by CETs, measuring times of several weeks will be required. Due to the fundamental role of the SRT in modem physics, this new experimen­
tal test described here is highly important.
References
1. Dirac, P. A. M., Nature 168 (1951), 906. 2. Kholmetskii, A. L., Physica Scripta 55 (1997), 18. 3. Kholmetskii, A. L., Physica Scripta 67 (2003), 381. 4. Kholmetskii, A. L., Hyp. Interact. 126 (2000), 411. 5. Rohlsberger, R., Toellner, T. S., Sturhahn, W, Quast, K. W, Alp, E. E., Bernhard, A., Burkel, E.,
Leupold, O. and Gerdau, E., Phys. Rev. Lett. 84 (2000), 1007. 6. Rohlsberger, R., Quast, K. W, Toellner, T. S., Lee, P., Sturhahn, W, Alp, E. E. and Burkel, E.,
Appl. Phys. Lett. 78 (2001), 2970.
Hypeifine Interactions 156/157: 15-19,2004. © 2004 Kluwer Academic Publishers.
Mossbauer Spectrometer with Novel Moving System and Resonant Detection of Gamma Rays
MIROSLAVMASHLAN1, VIKTOR YEVDOKIMOV2, JIRIPECHOUSEK1,
RADEK ZBORIL3 and ALEXANDER KHOLMETSKII2
1 Department of Experimental Physics, Palacley University, Svobody 26, 771 46 Olomouc, Czech Republic 2 Department of Physics, Belorussian State University, Skoriny Ave 8, Minsk, Belarus 3 Department of Physical Chemistry, Palacley University, Svobody 8, 771 46 Olomouc, Czech Republic
15
Abstract. A Mossbauer spectrometer with the collective synchronous motion of the radioactive source and resonant detector has been built. The new special transducer with four drive coils and one velocity pickup coil has been developed. The polyamide fibers serve as suspension brackets, barium ferrite magnets are used. The mechanical construction of transducer allows using different cryostats and furnaces, because the sample is immovable. The resonant detector consists of the thin foil of the organic plastic scintillator with the dissolved substance converting the resonant gamma rays to conversion electrons.
1. Introduction
There are two main advantages of the resonant detection of gamma rays in compari­ son to standard detection in Mossbauer spectroscopy. Firstly, the better signal/noise ratio reduces the time period necessary to the spectrum accumulation [1, 2]. Sec­ ondly, the narrower line width allows better to resolve the various Mossbauer sub spectra [2-4]. On the other hand, the necessity to use the moving sample re­ stricts the application of both cryostats and furnaces. Principally, the use of the collective synchronous motion of a radioactive source and a resonant detector al­ lows taking advantages of resonant detection of gamma rays. Just one attempt to use the synchronous "source-detector" motion has been made by Maltsev et al. [5], but they obtained the satisfactory results only with the harmonic motion.
A Mossbauer spectrometer with resonant detection of gamma rays and with the new special transducer is presented in this paper. Mossbauer spectrum can be accumulated in constant acceleration and constant velocity modes.
2. Moving system
The special transducer of double-loudspeaker type (Figure 1) uses four drive coils (diameters of 24.4 mm), which are made of copper wire (diameter of 0.1 mm). The
16 M. MASHLAN ET AL.
1-----------------, I I
: 4 : I I L _______________ __ I
Figure 1. The draft of transducer: 1 - drive coils, 2 - velocity pickup coil, 3 - suspension brackets, 4 - detector unit, 5 - source, 6 - sample, 7 - cryostat, 8 - magnetic systems.
10
o
Figure 2. The amplitude and phase frequency characteristics.
resistance of each drive coil is about 16 n. The velocity pickup coil (diameter of 27.4 mm) of this transducer is made of 0.07 mm diameter copper wire and its re­ sistance is about 450 n. The barium ferrite magnets of the 10 mm high toroid with inner and outer diameters of 32 mm and 72 mm, respectively, are used. Polyamide threads fix the moving part. The transducer amplitude and the phase frequency characteristics are shown in Figure 2. It is obvious that the resonance frequency is about 12 Hz.
Figure 3 shows the schematic circuit diagram of the control drive unit, which consists of the amplifier of the velocity pickup coil signal (102), the summator of the reference velocity and the velocity pickup coil signal (101), the integrator of the velocity pickup coil signal (I04A) for correction of error signal, the summator of the error signal with first integral of the velocity pickup coil signal (I03A), the PID­ controller (I03B), the integrator for correction of dc signal (I04B) and the power
MOSSBAUER SPECTROMETER
BNl v(t)
4Kl
Figure 3. Schematic circuit diagram of the control drive unit.
amplifier with local feedback (105, Tl, T2). The amplitude and phase frequency characteristics of this control unit are adjusted for the specific transducer [6].
3. Detection system
A thin foil of organic plastic scintillator with dissolved substance of the "reso­ nant gamma rays-electron" convertor (RGEC) constitutes the fundamental element of the detector unit. The principle of operation of resonant scintillation detec­ tor is as follows. The resonant gamma photons excite the nuclei of the RGEC grains. In the case the nuclei deexcite by emission of conversion electrons, these electrons will excite along their paths the atoms of the plastic scintillator, which surrounds the RGEC grains. The excited atoms of the scintillator produce pho­ tons, which the photoelectronic mUltiplier tube registers. As the RGEC, 1l9Sn0 2
and K2Mg[57Fe(CN)6]·H20 are used for 119Sn and 57Fe Mossbauer measurements, respectively. The resonant scintillation detector unit (Figure 4) uses the photomul­ tiplier tube R1924A (Hamamatsu) that is characterized by bialkali photocathode, typical current amplification of 1.1 x 106, and spectral range from 300 to 650 nm (peak wavelength is 420 nm), and low dimension (diameter and length are 25 and 43 mm, respectively). The output signal of the photomultiplier tube is amplified by means ofthe C6438 (Hamamatsu) fast preamplifier. The fast pulse-height discrimi-
18 M. MASHLAN ET AL.
y - ray Plastic Fast ... Fast
----- scintillator + Photomultiplier ~ preamplifier II" pulse-height ~ RGEC RI924A C6438 discriminator
Figure 4. Schematic draft of detection system.
Table I. Results of the nonlinearity measurements
2 3 4 5 6
Ascending x(i) [mm/s] -8.073 -4.348 -0.826 1.801 5.323 8.622
part non(i) [%] 0.11 -0.10 -0.03 -0.04 -0.03 0.08
Descending x(i) [mm/s] -8.074 -4.348 -0.824 1.803 5.319 8.623
part non(i) [%] 0.11 -0.10 -0.03 -0.02 -0.05 0.09
nator [7] filters the pulses of the preamplifier output in accordance with Mossbauer resonance gamma rays.
4. Results and discussion
The main parameter characterising the quality of a Mossbauer spectrometer is the nonlinearity of the velocity scale. The following algorithm was used for an estimation of the nonlinearity. The spectral lines of the a-Fe203 Mossbauer spec­ trum, accumulated in 1024 channels, were approximated by Lorentz functions. The nonlinearity for all line positions were calculated by means of fitting of the experimental position of the spectral lines to its theoretical positions by a least square method and by means of the relation
. xU) - a . v(i) - b non(l) = v(6) - v(1) ,
where i (i = 1--6), xCi), v(i), a, b are line number, experimental position of the line, theoretical position of the line, parameters obtained from least square method, respectively. The unfolded spectrum was used for the qualitative test of the equip­ ment. The experimental positions of lines and their nonlinearities are shown in Table I.
Two Mossbauer spectra ofthe BaSn03 absorber were measured by a YAI03(Ce) scintillation detector and by a resonance scintillation detector to compare the res­ onance effect and the line width parameters. The geometries of the experiments were the same. The results of spectra fitting are summarized in Table II. Clearly the Mossbauer effect is significantly higher and the line width narrower with using the resonance detector.
MOSSBAUER SPECTROMETER
Resonance effect [%]
7
0.942
35
0.825
19
The novel equipment significantly improving the efficiency of the Mossbauer mea­ surements and the precision of their results was constructed. New transducer that allows the application of cryostats and furnaces is fully comparable with others double-loudspeaker type transducers. Using such transducer and the resonance scintillation detector the higher signal/noise ratio and narrower line width were obtained in comparison to the conventional equipments.
Acknowledgement
Financial support from The Ministry of Industry and Trade of the Czech Republic under project PROGRES FF-PIl08 is gratefully acknowledged.
References
1. Kholmetskii, A. L., Mashlan, M., Misevich, 0. v., Chudakov, V. A., Lopatik, A. R. and Zak, D., NucZ. Instrum. Meth. B 124 (1997), 143.
2. Maltsev, Y., Mehner, H., Menzel, M. and Rogozev, B., Hyp. Interact. 139-140 (2002), 679. 3. Mitrofanov, K. P., Illarionova, N. V. and Shpinel, Y. S., Prib. Tekhn. Eksp. 30 (1963), 49. 4. Odeurs, J., Hoy, G. R., L' Abbe, c., Koops, G. E. J., Pattyn, H., Shakhmuratov, R. N.,
Coussement, R., Chiodini, N. and Paleari, A., Hyp. Interact. 139-140 (2002), 685. 5. Maltsev, Y., Mehner, H., Menzel, M. and Rogozev, B., In: Program and Abstracts, ICAME'99,
Garmisch-Partenkirchen, 29 August-03 September 1999, T9/35. 6. Evdokimov, V. A., Mashlan, M., Zak, D., Fyodorov, A. A., Kholmetskii, A. L. and Misevich,
O. v., NucZ. Instrum. Meth. B 124 (1995), 287. 7. Mashlan, M., Jancik, D. and Kholmetskii, A. L., In: M. Miglierini and D. Petridis (eds.), Moss­
bauer Spectroscopy in Materials Science, Kluwer Academic Publishers, Dordrecht, Boston, London, 1999,p. 391.
Hyperfine Interactions 156/157: 21-26,2004. © 2004 Kluwer Academic Publishers.
21
in Fe304 and Fe66Nh4 from Mossbauer Polarimetry
K. SZYMANSKIl , D. SATULAl and L. DOBRZYNSKIl ,2
llnstitute of Experimental Physics, University of Bialystok, 15-424 Bialystok, Poland 2The Soltan Institute for Nuclear Studies, 05-400 Otwock-Swierk, Poland
Abstract. Experimental determination of some angular averages of hyperfine field is demonstrated. The averages relates to magnetic structure. Exemplary results of the measurements for Fe304 and Fe66Ni34 show that it is possible to obtain valuable information about the field magnitudes and orientations even when distributions of fields are present in the system under study.
In disordered magnetic systems one encounters usually a distribution of both, the intensity and the orientation of hyperfine magnetic field (h.mJ.). Preferred orientation, P(Q), of the hyperfine fields is of particular importance in the con­ text of the contribution of selected elements to the magnetic texture [1, 2]. It is usually described in a certain set of basis functions, e.g., spherical harmonics Y1m •
Since only Ml dipolar transitions are measured in 57Pe Mossbauer spectroscopy, unpolarized radiation delivers information on Y2m only, while Ylm harmonics can be known when circularly polarized radiation is used [3]. Knowing Ylm and Y2m in the texture function is equivalent to the knowledge of angular averages (Yr' m) and (Yr' m)(ys . m»)[4], where m is an unit vector parallel to the local hyperfine field B, Yr is a Cartesian versor (r = x, y, z) and brackets () denote angular averaging:
(J(Q)} = 1 J(Q)P(Q) dQ. 41l'
(1)
In the case of a sample with axial symmetry it is convenient to choose one of the Yr, denoted by y, parallel to the k vector of photon. Then the averages (y . m) == Cl and (y . m)2) == C2 can be measured with monochromatic, circularly polarized radiation [4, 5]. In disordered systems one can measure distribution of the intensity ofh.mJ., p(B), and for each intensity B, in principle, two averages Cl
and C2. This paper shows that one can finally get three distributions: p(B), Cl (B) and c2(B).
Normalized Mossbauer spectrum S(v) consists of a linear combination of N subspectra s(v, B i ):
N
(2)
22 K. SZYMANSKI ET AL.
where v is Doppler velocity, and p j is a nonnegative coefficient for a field B j. Subspectrum s(v, B) is a Zeeman sextet:
6
s(v, B) = I>nLn(V, B), (3) n=1
where Ln (v, B) describes the shape of the absorption line corresponding to the nth nuclear transition and in is the line intensity dependent on the photon polarization and wave vector. For the case of single B and measurements with circularly polar­ ized radiation, the coefficients in were given in [3]. One can show [4] that having a distribution of directions of vector B the expressions for in should contain already introduced averages, namely:
16iI =48i4=3(1 ±2CI +C2), 4i2 =4is = 1- C2,
48i3 = 16i6 = 3(1 =f 2CI + C2). (4)
Every sub spectrum s(v, Bj ) is characterized by its relative area proportional to p j and two averages CI and C2 (the index j in CI, C2 as well as in p coefficients was dropped for simplicity reasons). Using the least squares fitting procedure and varying 3N coefficients p, CI and C2, one can find best fit of function S(v), see Equation (2), to the experimental spectrum. Physically possible sets of p, CI and C2 have to be considered only, namely:
p ~ 0, -1 ~ CI ~ 1, 0 ~ C2 ~ 1, (5)
The last inequality in (5) is the Buniakovsky-Schwartz relation. In order to make minimisation of X2 with conditions (5) effective, we introduce a set of 3N new variables, a, b, ~,related to p, CI and C2 through:
(a2 + b2)2 + 2~4 p[a,b,~] = 4 '
a4 _ b4
cI[a, b, ~] = (a2 + b2)2 + 2~4' (6)
(a2 _ b2)2 + 2~4 c2[a, b, ~] = (a2 + b2)2 + 2~4'
The square brackets were used in transformation functions (6) in order not to con­ fuse them with the distribution functions pCB), CI (B) and c2(B). The functions (6) have following properties: (i) they are even, (ii) for a, b, and ~ positive there exist inverse functions a[p, CI, C2], b[p, CI, C2], ~[p, CI, C2], (iii) the inequalities (5) hold for any real values of a, b, and ~, (iv) X2 expressed in variables a, b, and ~ is a polynomial of 8th order. The two last properties make numerical process of searching of minimum of X 2 very effective.
Two different distributions of hyperfine parameters may produce identical spec­ tra. This leads to the ambiguity much discussed in literature [6-8]. One case of
ANGULAR DISTRIBUTION OF H.M.F. 23
Table I. Fitted probabilities p and magnetic texture coefficients. Two last columns contain average value of the h.m.f. and the width of its Gaussian distribution
p C[ C2 B [T] fl.B [T]
Fe304 0.38 ±0.01 -0.78±0.02 0.93 ± O.ol 49.92 0.18
0.62 ± O.ol 0.80±0.02 0.97 ± 0.01 45.13 0.53
FeO.66Nio.34 0.37 ± 0.02 0.57 ±0.03 0.60± 0.02 28.6 2.04
0.29 ±0.Q2 0.62 ± 0.03 0.62 ± 0.02 25.2 3.36
0.34 ± 0.02 0.44 ± 0.03 0.63 ± 0.02 17.7 6.45
ambiguity appears when multidimensional distribution is extracted from one di­ mensional data (i.e. Mossbauer spectrum). Additional independent experimental information usually reduces this ambiguity. We have demonstrated [9], as an ex­ ample, that two different distributions of h.mJ. reproduce experimental spectra of Fe2.5Cro.5Al alloy measured with unpolarized beam equally well. The measure­ ments with monochromatic, circularly polarized radiation, showed which of the two is correct one. Continuing this direction we developed an algorithm for simul­ taneous fitting of the spectra measured with different photon polarization states (on the sample in the same conditions, like external magnetic field, temperature). Three distributions: pCB), Cl (B) and c2(B) are fitted simultaneously with the help of transformation (6).
In order to apply discussed algorithm to real cases, we have to take into account different isomer shift and quadrupole splitting for every subspectra (the latter is considered as small perturbation of the h.m.f.), and correction for polarization degree [4,10].
The first example on which the algorithm was tested is Fe304 powdered ab­ sorber, prepared from stoichiometric single crystal of magnetite, with stoichiome­ try for which Vervey transition of the first kind is observed. The absorbers exposed to external field of 1.1 T were measured at room temperature and the spectra are shown in Figure 1. Fe304 is ferrimagnet and one expects that in an external magnetic field two hyperfine fields will be oriented antiparallel, resulting in Cl parameters of opposite signs. This is observed indeed, see Table 1. Results of si­ multaneous fit are shown by solid lines in Figure 1. Majority of the Fe moments, occupying octahedral positions with smaller h.mJ. are oriented parallel to the net magnetization, like in a-Fe (see the inset), and the Cl parameter is positive. Minor­ ity of Fe with larger field (occupying tetrahedral positions) are oriented antiparallel to the net magnetization which is measured quantitatively by negative value of Cl parameter. Absolute values of Cl and C2 parameters are slightly smaller than 1 in­ dicating almost complete saturation of the sample in the applied external magnetic field.
24
0;::;'
E (/) c ~ +-'
velocity [mm/s]
Figure 1. 1 Mossbauer spectra of Fe304 measured with two opposite circular polarizations of mono­ chromatic radiation. Solid lines show the best simultaneous fit obtained from algorithm discussed in the text. The inset shows schematically the shape of a-Fe spectra measured with two opposite circular polarizations abbreviated by t t and t -l- arrows.
The second example is Invar Fe-Ni alloy, whose ground state magnetic structure is still under debate. There are recent experiments performed under high pressure, one of them [11] consistent with 2y-state model proposed by Weiss [12], and other [13], consistent with low spin non-collinear structure proposed in [14]. Recent polarized neutron diffraction experiments indicated strong coupling of lattice and magnetic degrees of freedom [15]. Circularly polarized polychromatic radiation was used in investigation of Fe-Ni invar alloys [16], the spectra obtained were, however, complicated and difficult for interpretation.
In our experiment, Fe66Ni34 was prepared as a foil and measured in the magnetic field perpendicular to the foil at room temperature, see Figure 2. Three Gaussian components, displayed in the inset, describe full spectrum well. Results of the best fit are shown by solid lines in Figure 2; the fitted parameters are listed in the Table I. The most important result is, that the best fit is obtained for almost similar values of C2 (quite similarly for CI) for the three components. The smallest value of CI is related to the weakest h.mJ. This indicates that this component is more disordered than the remaining two. Our results leave no doubt that the lowest-field component
ANGULAR DISTRIBUTION OF H.M.F.
25
4 8
Figure 2. Same as Figure 1 for Fe66Ni34. The distribution of h.mJ. resulting from the components used is shown in the inset.
is neither due to the antiferromagnetic ordering postulated in 2y-state model [12] nor to eventual random disorder. Were any of these two possibilities true, the c]
should be close to 0.06, i.e. the ratio of the applied field and the mean value of the component (1.1/17.7), while C2 would be close to 1/3. Moreover our results show that low field component does not have, in average, anti parallel orientation with respect to the net magnetization as interpreted in [16].
References
1. Pfannes, H.-D. and Fisher, H., Appl. Phys. 13 (1977),317. 2. Pfannes, H.-D. and Paniago, R. M., Hyp. Interact. 71 (1992), 1499. 3. Frauenfelder, H., Nagle, D. E., Taylor, R. D., Cochran, D. R. F. and Visscher, W. M., Phys. Rev.
126 (1962), 1065. 4. Szymanski, K., NIM B 134 (1998), 405. 5. Szymanski, K., Dobrzynski, L., Prus, B. and Cooper, M. 1, NIM B 119 (1996), 438. 6. Le Caer, G., Dubois, 1 M., Fischer, H., Gonser, I. U. and Wagner, H. G., NIM B 5 (1984), 25. 7. Le Caer, G. and Brand, R. A., 1. Phys.: Condens. Matter 10 (1998), 10715. 8. Rancourt, D. G., In: G. 1 Long and F. Grandjean (eds), Mossbauer Spectroscopy Applied to
Magnetism and Materials Science, Vol. 5, Plenum, New York, 1996, p. 105. 9. Szymanski, K., Satula, D. and Dobrzynski, L., 1. Phys.: Condo Matter 1 (1999), 881.
26 K. SZYMANSKI ET AL.
10. Szymanski, K., J. Phys.: Condo Matter 12 (2000), 7495. 11. Rueff, J. P., Shukla, A., Kaprolat, A., Krisch, M., Lorenzen, M., Sette, F. and Verbeni, R., Phys.
Rev. B 63 (2001), 132409. 12. Weiss, J., Proc. R. Soc. London A 82 (1963), 281. 13. Dubrovinsky, L., Dubrovinska, N., Abrikosov, I. A., Vennstrom, M., Westman, F., Carlson, S.,
van Schilfgaarde, M. and Johansson, B., PRL 86 (2001),4851. 14. van Schilfgaarde, M., Abrikosov, I. A. and Johansson, B., Nature 400 (1999), 46. 15. Brown, P. J., Kanomata, T., Matsumoto, M., Neumann, K.-U. and Ziebeck, K. R. A., JMMM
242-245 (2002), 781. 16. Ulrich, H. and Hesse, J., JMMM 45 (1984), 315.
Hyperfine Interactions 156/157: 27-30, 2004. © 2004 Kluwer Academic Publishers.
Two-Dimensional Mossbauer Spectra
YD. MALTSEyl, S. MALTSEy2, M. MENZEU,*, B. ROGOZEy2 and A. SILYESTROy3
1 Federal Institute for Materials Research and Testing (BAM), Richard-Willstiitter-Strasse Il, D-12489 Berlin, Germany; e-mail: MichaeI.Menzel@BAM.DE 2Radium Institute, 2nd Murinsky Avenue, 28, 194021 St. Petersburg, Russia 3 RITVERC GmbH, 2nd Murinsky Avenue, 28, 194021 St. Petersburg, Russia
27
Abstract. To decrease the spectra measurement time in Mossbauer spectroscopy a new data acqui­ sition system was proposed, which allows to collect data as a two-dimensional distribution.
Key words: data acquisition, signal processor, two-dimensional Mossbauer spectrum.
1. Introduction
In spite of all advances in electronics, the design of Mossbauer spectrometers has not advanced principally. The usual arrangement [1] for collecting a Mossbauer spectrum is shown in Figure 1 (a). The main disadvantage of this arrangement is the occurrence of pulse overlapping at high count rates, it is when the next pulse "sits on the tail" of a previous one. In this case a single channel analyzer (SCA) registers the noise pulses and misses the pulses from needed quanta, which will shift out of the working window. Pulse overlapping disturbs the amplitude spectrum, reduces the signal/noise ratio in the Mossbauer spectrum, limits the maximal count rate of the data acquisition system, and, finally, increases the duration of experiment. An­ other disadvantage of the conventional arrangement is the difficulty in setting the SCA window if the amplitude spectrum has the well-known "exponential decay" shape using CEMS or resonance detectors.
Therefore, a data acquisition system, which is free of these disadvantages, was created.
2. Proposed data acquisition system
The scheme of the proposed data acquisition system is shown in Figure l(b). It consists of a fast analog-to-digital converter (ADC) AD9224 chip, signal processor (SP) ADSP-21061 chip, and random access memory (RAM).
The ADC digitizes the signals from the detector with a sampling rate of up to 40 million times per second. The signal processor determines the local maximum
* Author for correspondence.
L __________ J
Figure 1. (a) Conventional scheme, where: S - source; A - absorber; VT - velocity transducer; DU - driving unit; D - detector; SCA - single channel analyzer; MCS - multichannel scaler; PC - personal computer. (b) Proposed scheme, where: ADC - fast analog-to-digital converter; SP - signal processor; RAM - random access memory; 2DA - "Two-dimensional analyzer".
and local minimum values, and calculates the correct amplitude for each pulse. Thus, pulse overlapping is eliminated. The operation of the SP is synchronized with the driving system by the signals START and "channel advance" CHA. Using the pulse amplitude in a digital form and the current velocity channel number SP forms a two-dimensional (2D) distribution of pulses in the RAM, where the Y-axis corresponds to the velocity scale, and the X-axis corresponds to the amplitude of pulses from the detector.
3. Experimental results
Examples of two-dimensional Mossbauer spectra are shown in Figures 2 and 3. Cross-sections parallel to the velocity-counts-plane give Mossbauer spectra,
which correspond to different amplitudes of input pulses. Cross-sections parallel to the energy-counts-plane give amplitude spectra, which correspond to different values of the Doppler velocity.
Figure 2 presents a two-dimensional Mossbauer spectrum of an iron foil mea­ sured with a proportional counter. There are 6 dips on the 14.4 ke V billow and there are 6 small peaks on the 6.3 keY X-rays billow. This example illustrates, that with the new instrumentation absorption and emission spectra are acquired simultaneously.
TWO-DIMENSIONAL MOSSBAUER SPECTRA
19 -9
Figure 2. Two-dimensional Mossbauer spectrum of an iron foil, measured with a proportional counter.
700000 ~
- . • \"1'\\"1'\ -3 .5 -2 .5 "\]0\0:.\\'1'
Figure 3. Two-dimensional Mossbauer spectrum of FeC204 ·2H20, measured with a resonance scintillation detector.
30 YU. MALTSEV ET AL.
Figure 3 presents a two-dimensional Mossbauer spectrum of a FeC20 4·2H20 sample measured with a resonance scintillation detector [2]. It consists of a set of absorption Mossbauer spectra with different signal/noise ratios. The optimal energy "window" can be chosen after the experiment. But from the precision point of view, the best procedure would be to fit each partial Mossbauer spectrum inde­ pendently, and to calculate the weighted averages of the spectral parameters. This technique reduces the estimated standard deviation by a factor of 1.4 and more, or reduces the data acquisition time by a factor of 2.0 and more.
4. Conclusions
The proposed setup allows to collect more information about the sample in one experiment, and, finally, saves data acquisition time.
The use of a fast ADC together with a modem digital signal processor signif­ icantly increases the count rate of Mossbauer spectrometer due to the elimination of pulse overlapping.
The application of a two-dimensional data acquisition system allows to chose the optimal energy "window" in the amplitude spectrum after the experiment, and to measure gamma-quanta absorption and X-rays emission spectra simultaneously in the same transmission experiment. In the case of low count rates the proposed scheme also saves data acquisition time, because amplitude and Mossbauer spectra are collected simultaneously.
In the case of CEMS measurements a single experiment gives a number of Mossbauer spectra, which correspond to different surface layers of the sample.
References
"
57Pe Mossbauer Study of Magnetic N anowires
DE-SHENG XUE and FA-SHEN LI Key Laboratory for Magnetism and Magnetic Materials of the MOE, Lanzhou University, Lanzhou 730000, P R. China
31
Abstract. Nanowires of metal, alloy, compound, and ferrite have been electrodeposited in anodic aluminium oxide templates. The structure and magnetic properties of the nanowires are characterized by 57pe Mossbauer spectroscopy combining with other techniques. It is found that the metal and alloy nanowires have a very strong magnetic anisotropy. The surface distribution of the magnetic moment is different from that of the interior. The Debye temperature of Prussian blue nanowires derived from hyperfine interaction parameters is lower than that of the bulk. The properties of the ferrite nanowires are strongly related to the structure of nanowires.
Key words: nanowires, Mossbauer spectroscopy.
1. Introduction
There has been a rapidly increasing interest in one dimension nanostructure, such as nanotubes, nanowires, nanorods, and nanobelts, because of their potential for fundamental studies of the size effect and for their applications in nanodevices [1,2]. Since theoretical predictions suggest that one-dimensional Ising model shows no magnetic ordering at nonzero temperature [3, 4], it is an informative way to understand the theoretical result by fabricating and studying the nanowire of molecular-based magnet. From the point of view of applications, the magnetic nanowire arrays are of interest for magnetoresistive devices of very small size [5] and for high-density recording media [6]. For instance, the density in conven­ tional longitudinal recording may be less than 50 Gb/in2 because of the thermal stability [7]. However, the density of the arrays may potentially be higher than 100 Gb/in2 [8].
Among known approaches for producing nanostructures, the anodizing anodic aluminum oxide (AAO) template-based method is a popular approach to synthesize a variety of metal and semiconductor nanowires through electrochemical technol­ ogy [9]. Recently, Fe [10], Fe-Co [11], Fe-Ni [12], Fe203 [13], FeOOH [14] and Prussian blue [15, 16] nanowire arrays embedded in AAO templates have been successfully fabricated. The recent development of metal amorphous nanowires arrays such as CoP, FeP and NiP is another highlight [17]. In this paper, combining with other measurement techniques, the information about micro electronic, mag­ netic and structural properties of the nanowires are studied by the 57Fe Mossbauer spectroscopy.
32 D.-S. XUE AND F.-S. LI
2. Experimental
The highly ordered porous AAO templates were generated by anodizing aluminum foils (99.999%) in an oxalic acid solution using a two-step anodizing process [15]. Metal, alJoy and compound can be directly fabricated by using the AC electrode­ position method with a standard double-electrode celJ [10, 12, 15]. The ferrite nanowires can be formed by heat-treating FeOOH at different conditions [13]. The images of AAO template, Fe naowires, Prussian blue nanowires and Fe304 nanowires are shown in Figures l(a)-(d), respectively.
Structural characterization was performed by means of X-ray diffraction (XRD) using a RigakulMax-2400 diffractometer with Cu K a radiation. Transmission elec­ tron microscopy (TEM) and selected area electron diffraction (SAED) were per­ formed by using a JEO 2000 microscope, while scanning electron microscopy (SEM) was operated by using JSM-5600 microscope. The Mossbauer spectroscopy (MS) was obtained by using a constant acceleration with a source of 57 Co in rhodium. The spectra were fitted with Lorentz lines, and the isomer shifts (IS) were referred to that of a-Fe at room temperature (RT).
500 nm 200 nm
Figure 1. (a) SEM image of porous anodic aluminium oxide template, (b), (c), (d) TEM images of iron, Prussian blue and Fe304 nanowire, respectively.
57Fe MOSSBAUER STUDY OF MAGNETIC NANOWlRES 33
3. Results and discussion
ARRAYS
3.1.1. Fel-xNix nanowire arrays
Fel - xNix (0 < x ~ 0.32) nanowire arrays with 16 nm in diameter, 4 /Lm in length were prepared. The results of XRD showed that the nanowire arrays have a bcc structure with [110] crystallographic orientation along the nanowire axis [12]. The MS obtained for the Fel-xNix nanowires are shown in Figure 2. Each spectrum consists of a doublet and a sixtet, which are ascribable to a paramagnetic and a magnetic phase, respectively. The vanishing of the second and fifth peaks in the MS indicates that the magnetic moments of the iron atoms in the Fel-xNix nanowire arrays align on the [110] direction. This means that there is a strong shape anisotropy in [110] direction.
The fitting results of each magnetic spectrum for Fel-xNix nanowire arrays are listed in Table I. The observed linewidths (FWHM) of the MS indicate that the
1.00
0.98
1.00
1.00 ..... E (I)
Q) 0:::
Relative velocity (mm/s)
Figure 2. The room-temperature Mossbauer spectra of Fel _x Nix nanowire arrays.
34 D.-S. XUE AND F.-S. LI
Table I. Hyperfine parameters of Fel-xNix nanowire ar­ rays at room temperature: FWHM is the linewidth of the Mossbauer spectrum; 8 is the isomer shift; Q S is the quadruple splitting; Hhf is the hyperfine field
FWHM IS QS Hhf (mms-l) (mms- 1) (mms- I ) (kOe)
x = 0.03 0.37 0.00 0.00 333
x = 0.13 0.41 0.02 0.00 338
x = 0.15 0.43 0.02 0.00 339
x = 0.25 0.46 0.02 0.00 342
x = 0.32 0.59 0.01 0.00 338
local environment of iron atoms changes with the substitution of Ni content. The quadruple splittings (QS) of Fel-xNix nanowires are equal to zero, which suggests that the structure of nanowires still keeps in a cubic symmetry. The IS has little dependence on Ni content. The nickel composition dependence of the hyperfine field (Hhf) shows a maximum at x = 0.25, which is consistent with the bulk and the fine particles of Fel_xNix alloy [18].
3.1.2. Fe nanowire arrays
In order to understand the distribution of the magnetic moment in metal, the Fe nanowire arrays were fabricated. The conversion electron Mossbauer spectrum (CEMS) was performed on the top of a-Fe nanowire arrays. The CEMS spectra of three samples: (a) a-Fe nanowire arrays with diameters d = 60 nm, (b) a-Fe nanowire arrays with d = 300 nm, (c) a-Fe foil with 25 /Lm in thickness, are shown in Figure 3. It is found that the Hhf is similar to that in bulk iron, and the FWHM increases with the decreasing diameter of a-Fe nanowires, which indicate that with increasing diameter of nanowires the influence of magnetocrystalline anisotropy becomes more important. The ratio between the second peak and the first peak (/2/ II) is 0.215 for d = 300 nm while it is 0.089 for d = 60 nm. The ratio for the a-Fe foil equals 1.179, which shows the magnetic moment departure from the nanowire axis direction as the diameter of nanowires increase.
Based on the experimental observations, we assume a core-shell structure model, in which the core spins are magnetically coupled, but the surface spins are ther­ mally disordered because of reduction in Fe coordination. The evidence for such a spin configuration comes from the MS measured at RT as shown in Figure 4, the surface spins are thermally activated as paramagnetic contribution, resulting in a central single peak of the Mossbauer spectra, the relative intensity of which is enhanced with decreasing diameter of the Fe nanowire arrays.
57Fe MOSSBAUER STUDY OF MAGNETIC NANOWIRES 35
1.02 ",-----.----------,
3.2. LOW-DIMENSIONAL EFFECT ON PRUSSIAN BLUE NANOWIRES
Prussian blue analogs have played an important role in molecular magnets, and a number of unusual properties were found [19-21]. In our pioneer work, the Curie temperature of highly ordered Prussian blue nanowires embedded in AAO tem­ plates was found to been reduced with respect to Prussian blue bulk, resulting from the diminution of the average number of the nearest magnetic interaction neighbors and magnetic exchange interaction constants as the diameters of nanowires de­ creasing [15]. In order to have a deep look of the chemical binding in the nanowires, the IS, QS and the recoil-free fraction (f) were employed.
The highly ordered Prussian blue nanowires with diameter of about 50 nm and length up to 4 {tm were electrodeposited into AAO templates. The Mossbauer spectra measured at 15, 77, 150, 230, and 290 K, are shown in Figure 5. Each of the spectra consists of a doublet and a singlet, which are ascribable to the high spin Fe3+ ions and low spin Fe2+ ions, respectively [16]. The temperature dependence of isomer shift (IS) and the spectra area can be fitted by the following Equations (1) and (2), respectively,
3k T[38 (T)318/T ] 8S0D = __ B _ __ + 3 - x3 (eX - 1) dx , 2Mc 8T 8 0
(1)
36
~ 0.98 COS :: 0.97
0.97
·10 -1l ~ -4 .2 0 2 4 6 8 10 Relative velocity (mm/s)
D.-S. XUE AND F.-S. LI
Figure 4. The room-temperature Mossbauer spectrum of a-Fe nanowires with different diameters.
{ 3 ER [ (T)21 G/T xcix ]} /=exp---1+4- --, 2 kBG G 0 eX - 1
(2)
where k B is the Boltzman constant, G is the Debye temperature, M is the atomic mass, c is the velocity of light and E R is the recoil energy. The obtained results show that the Debye temperature (226 ± 5 K) of Prussian blue nanowires decreases with respect to (257 ± 5 K) of Prussian blue bulk, which indicates the strength of the forces binding iron ions in Prussian blue nanowires become smaller, as Prussian blue become a nan ow ire from a three dimension solid.
3.3. PHASE ANALYSIS OF FERRITES NANOWIRE ARRAYS
The ,B-FeOOH nanowires with diameter of 120 nm and length about 6 /Lm em­ bedded in AAO template were prepared. However, it is difficult to check the phase because of its amorphous state. Prior work by Chambaere et ai. showed that there are two doublets with an intensity ratio of 60 : 40 in MS of ,B-FeOOH. The QS of the doublet with intensity of 60% is 0.51-0.56 mmls while the QS of the doublet with intensity of 40% is 0.92-0.96 mmls, the IS of the two doublets are 0.37 mmls
57Fe MOSSBAUER STUDY OF MAGNETIC NANOWlRES 37
. ....
. ~ ro Qi 0::
Relative velocity (mm/s)
Figure 5. The Mossbauer spectrum of Prussian blue nanowires obtained at different temperatures.
c:; 1.00 h\iI'Ir./\MIiWIII'lII!\NflItI.UIl.\ o ...... til til ..... E til C (1j I-< 0.99 +> (I)
> ...... -+-' (1j ..... (I)
0::: 0.98
-10 -8 -6 -4 -2 0 2 4 6 8 10
Relative velocity (mm/s) Figure 6. The room-temperature Mossbauer spectrum of ,B-FeOOH nanowire arrays.
and 0.38 mmls respectively [22]. The MS of the FeOOH nanowire arrays mea­ sured at RT is shown in Figure 6. The average IS and QS are 0.35 mm1s and 0.74 mm1s, respectively. They are in agreement with the hyperfine parameters of Fe3+ in ,B-FeOOH compounds.
Magnetite nanowire arrays were synthesized in the holes of AAO by heat­ treating the precursor ,B-FeOOH at 600 K for 3 h in H2 . The nanowires have
38 D.-S. XUE AND F.-S. LI
1.00
t:: 0 ....... Vl 0.99 Vl ....... E3 Vl t:: (\) 0.98 H ~
<l> > ...... ~
0.97 (\j -<l> 0::
-10 -8 -6 -4 -2 0 2 4 6 8 10
Relative velocity (mm/s)
Figure 7. The room-temperature Mossbauer spectrum of Fe304 nanowires arrays.
a spinel structure and each nanowire is composed of fine crystallites with size of about 15-40 nm. However, the XRD patterns of Fe304 are almost similar to that of the y-Fe203 due to their similarity in crystal structure. MS was used to verify the phase and study the micro-magnetic properties of Fe304 nanowires. It is known that the differences of the Mossbauer parameters between Fe304 and y­ Fe203 are: (1) the value of QS in Fe304 is closer to zero than that in y-Fe203; (2) the values of the Hhf corresponding to A and B sites are different in Fe304, but almost the same in y-Fe203, due to the presence of Fe2+ ions at the A sites in Fe304 [23].
Figure 7 shows the MS of magnetite nan ow ires in AAO templates with the y­ ray normal to the surface of the membranes at room temperature, which consists of two sub-spectra of sextet and one doublet. The broadening peaks indicate there is a size distribution ofthe crystallites in the nanowires. In addition, 55% of the doublet is corresponding to a superparamagnetic phase, which is in good agreement with the results of XRD and TEM [14]. The QS is -0.028 mm/s, and the Hhf of A and B sites are 47.3 and 43.9 T, respectively.
The larger difference of Hhf corresponding to A and B sites as well as the small value of QS indicate that the nanowires are Fe304 rather than y-Fe203. The less value of Hhf than that of the bulk materials is due to the existence of collective magnetic excitation caused by the size distribution of the crystallites [24]. The occupation ratio of the cations in A and B sites is 2 : 1, which is different from that of the bulk 1 : 2. It is also found that the intensity ratio of the sextet peaks is nearly 3 : 3 : 1, which suggests that the orientation of magnetic moments of the Fe304 crystallites is not along or perpendicular to the wire axis. This is also related to the competition of the shape and magnetocrystaline anisotropy.
57Fe MOSSBAUER STUDY OF MAGNETIC NANOWIRES 39
4. Conclusion
In summary, the metallic and non-metallic nanowires were successfully electrode­ posited in AAO templates. Mossbauer spectroscopy is very useful to identify the phase structure, the micro electronic and magnetic properties. It is found that the metal and alloy nanowires have very strong magnetic anisotropy, which make them good candidates for ultrahigh density magnetic recording materials. The surface distribution of the magnetic moment of a-Fe nanowires is different from that of the interior. The Debye temperature derived from hyperfine interaction parameters of Prussian blue nanowire is lower than that of the bulk. Ferrite nanowires can be prepared by heat-treating the precursor FeOOH, and the properties of the ferrite nanowires are strongly related to the structure of nanowires. The preparation of the ferrites and amorphous nanowires remain an open question.
Acknowledgement
This work is supported by the Trans-Century Training Program Foundation for the Talent of MOE, NSFC (Grant No. 10374038,50171032 and 10274027) and EYTT of China.
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40 D.-S. XUE AND F.-S. LI
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Hyperfine Interactions 156/157: 41-46,2004. © 2004 Kluwer Academic Publishers.
Synthesis and Mossbauer Study of Maghemite Nanowire Arrays
DE-SHENG XUE, LI-YING ZHANG and FA-SHENLI Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, People's Republic of China
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Abstract. Arrays of y-Fe203 nanowire were synthesized in anodic aluminum oxide templates. The structure, morphology and magnetic property at room temperature were characterized. Temperature­ dependent Mossbauer spectra was collected and the superparamagnetic relaxation was clearly ob­ served. Both hyperfine field and isomer shift increase with decreasing temperature. The anisotropy energy constant is determined from the reduction of the hyperfine field relative to the saturation value caused by the collective magnetic excitations.
Key words: maghemite, nanowires, Mossbauer spectrum.
1. Introduction
Maghemite, y-Fe203 has been attached much attentions in the magnetic recording media due to its attractive magnetic properties and chemical stability. In order to improve the magnetic recording density, y-Fe203 was diversely prepared. How­ ever, with the decreasing of the particle size superparamagnetism of the particle limits further development of y-Fe203 on ultrahigh magnetic recording density.
Nanowire arrays are promising candidates to extend this limit [1, 2]. Some metal and alloy nanowires, whose mag