Journal of Physics and Chemistry of Solids 72 (2011) 730–735

Contents lists available at ScienceDirect

Journal of Physics and Chemistry of Solids

0022-36

doi:10.1

n Corr

E-m

journal homepage: www.elsevier.com/locate/jpcs

The ESR study of single crystal spinel ZnCr2Se4 diluted with Sb and V

D. Skrzypek a,n, E. Malicka b, A. Cichon a

a A. Che!kowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Polandb Institute of Chemistry, University of Silesia, Bankowa 14, 40-007 Katowice, Poland

a r t i c l e i n f o

Article history:

Received 7 July 2010

Received in revised form

21 January 2011

Accepted 2 March 2011Available online 11 March 2011

Keywords:

A. Magnetic material

B. Crystal growth

D. Electron paramagnetic resonance

D. Magnetic properties

97/$ - see front matter & 2011 Elsevier Ltd. A

016/j.jpcs.2011.03.001

esponding author. Tel./fax: þ48 32 2588431.

ail address: Danuta.Skrzypek@us.edu.pl (D. Sk

a b s t r a c t

The single crystal of Sb3þ and V3þ doped zinc chromium selenide spinel ZnCr2Se4 were prepared by a

chemical transport method and characterized by ESR spectroscopy in order to examine the effect of

nonmagnetic antimony and magnetic vanadium on properties of the system. For antimony admixtures

the Neel temperature is very similar to that of the parent spinel ZnCr2Se4 (22 K). However, upon

incorporating vanadium ions, the TN temperature decreases down to 17.5 K, determined for the

maximum vanadium content (x¼0.06). The temperature dependence of the ESR linewidth over

paramagnetic region is interpreted by an occurrence of spin–phonon interaction. The strong broadening

linewidth together with its strong temperature dependence for vanadium doped ZnCr2Se4 is explained

by the complex paramagnetic relaxation model.

& 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Ternary selenide spinels exhibiting interesting structural,magnetic and electrical transport properties have been the subjectof numerous studies [1–12]. ZnCr2Se4 is a representative of thisclass of compounds; it is a cubic normal spinel with Zn2þ locatedat tetrahedral sites (A) and Cr3þ occupying octahedral [B] sites ofthe cubic close-packed array of selenium atoms [1–7]. Thephysical properties of ZnCr2Se4 related to the antiferromagneticbehavior (TN¼20 K) are described in [2–7]. Below TN the com-pound reveals a complex helimagnetic spin order, which resultsfrom competing ferromagnetic and antiferromagnetic interactions.In a number of papers it was shown that the physical properties ofspinel systems can be modified by different types and amountsof admixtures located at the tetrahedral and octahedral sites of thespinel structure. The influence of trivalent diamagnetic In, Ga andAl admixtures was reported in Refs. [13–20].

Recently, the structural and magnetic investigations ofZnCr2Se4 spinel doped with Sb and V ions were carried out[21–23]. The structure refinement was performed using theSHELXL-97 program package showing that all single crystal understudy have cubic structure with the space group Fd3m. The X-raydiffraction results show that the chromium and vanadium ionsoccupy the octahedral sites and the Sb3þ ions share the tetra-hedral positions with the Zn2þ ions, causing slight increase of theunit cell volume. However, the location of the Sb3þ ions in thetetrahedral voids implies some decrease in the total number ofthe Cr3þ ions for the electrostatic charge compensation. In all the

ll rights reserved.

rzypek).

samples of (Zn/Sb)–Cr–Se spinels a certain Cr deficit has beenobserved. Thus, the chemical formula was written as (Zn1�xSbx)[Cr2�x/3]Se4.

As expected, the magnetic characteristics of Sb3þ substitutedsystem are very similar to those of the parent compound ZnCr2Se4.The compounds studied are antiferromagnetical with Neel tem-perature TN¼22 K. On increasing Sb-content, some changes in thestrength of competing antiferromagnetic and ferromagneticexchange interactions are likely to occur, which is manifested viathe systematic decrease in the magnitudes of the magneticsaturation moment per Cr atom and the paramagnetic Curietemperature. The other magnetic results like the critical metamag-netic fields, the effective magnetic moments and the extent ofstrong spin fluctuations in the paramagnetic state are nearly thesame as in ZnCr2Se4. Upon incorporating vanadium ions intoZnCr2Se4 , the Neel temperature decreases down to 17.5 K, deter-mined for the maximum V content x¼0.06. Similarly, the decreaseof the paramagnetic Curie temperature upto 38 K was observed. Itmeans that the frustration, introduced into the systems by dilutionof the B-spinel sublattice with vanadium, reflects the change offerromagnetic interactions in the magnetic exchange.

The present work is a continuation of studies on the influenceof the trivalent ions: antimony and vanadium on the properties ofZnCr2Se4 spinel system. The ESR spectroscopic characterization ofthe single crystal of (Zn1�xSbx)[Cr2�x/3]Se4 and Zn[Cr2�xVx]Se4 isreported.

2. Experimental

Single crystal of the ZnCr2Se4 spinel with Sb and V admixtureswere grown by the method of chemical vapor transport with

D. Skrzypek et al. / Journal of Physics and Chemistry of Solids 72 (2011) 730–735 731

anhydrous chromium chloride, CrCl3, as the transporting agent.The details of the synthesis of the Zn1�xSbxCr2Se4 single crystalwere described elsewhere [21]. As starting materials for thegrowth of ZnCr2�xVxSe4 single crystal, the binary selenide ZnSe,elemental vanadium V and selenium Se (purity499.9%) wereused. The mixture of the substrates was sealed in quartzampoules (length �200 mm, inner diameter 20 mm) evacuatedto �10�3 Pa. These ampoules were heated in a horizontal zonefurnace to about 1162 K at the solution zone, maintaining atemperature gradient of 60 K along the ampoule. The furnacewas slowly cooled to room temperature after 10 days of heating.The obtained single crystal had a regular octahedral shape andwell-formed regular (1 1 1) faces with edge lengths of �1–3 mm.

Chemical composition of single crystal was determined byenergy-dispersive X-ray fluorescence spectrometry (EDXRF). Thesample was excited by the Rh target X-ray tube of 125 mmthickness Be window (XTF 5011/75, Oxford Instruments, USA).The X-ray spectrum from the sample was collected by thermoelec-trically cooled Si-PIN detector (XR-100CR Amptek, Bedford, MA,USA), having a resolution of 145 eV at 5.9 keV. The Si-PIN detectorwas coupled to the multichannel analyzer (PX4 Amptek, Bedford,MA, USA). The position of the sample was obtained using the X–Ystage and monitored by CCD camera and two laser pointers. Theapplied EDXRF spectrometer is described in detail in Ref. [24]. Thequantitative analysis of single crystal was performed by funda-mental parameters method. The results of EDXRF analysis togetherwith determined chemical formulae are shown in Table 1.

The electron spin resonance spectra were recorded with astandard ESR spectrometer operating at X-band (�9 GHz) fre-quency using 100 kHz field modulation. The microwave frequencywas measured using Hewlett Packard 534 microwave frequencycounter. The measurements were performed in the temperaturerange 3–400 K with an Oxford Instruments ESR 910 helium flowcryostat. The ESR spectra were recorded as the derivative dP/dB atdifferent temperatures. The values of ESR parameters, i.e. linewidth(DB) and resonance field (Br), were obtained from the best fit of thesimulated Lorentzian profile to the experimentally observed spec-tra. Fig. 1(a and b) shows the experimental and simulated ESRspectra at selected recording temperatures. In both cases, forZnCr2Se4 doped with antimony or vanadium, the nominal Sb andV content taken for the chemical syntheses was similar. The actualdopant concentration, derived for selected crystals from the EDXRFmethod, indicates differences in the amount of dopant. In our studya small, as-grown single crystal with the shape of octahedronwithout orientation of samples were measured.

Fig. 1. The experimental (dash) and simulated (solid) ESR spectra of ZnCr2Se4

doped: (a) antimony; (b) vanadium.

3. Results and discussion

3.1. The relaxation processes within paramagnetic region studied by

ESR method.

3.1.1. (Zn1�xSbx)[Cr2�x/3]Se4

Within the paramagnetic (PM) region, the ESR spectra of bothcrystals studied showed a single Lorentzian line with g¼1.99,

Table 1EDXRF analysis for single crystal of (Zn1�xSbx)[Cr2�x/3]Se4 and (Zn)[Cr2�xVx]Se4.

Chemical formula Zn Sb

(Zn0.98Sb0.01) [Cr1.98]Se4 13.2770.08 0.2970.04

(Zn0.97Sb0.02)[Cr1.99]Se4 13.0870.07 0.5670.05

(Zn1.06)[Cr1.96V0.04]Se4 14.270.2

(Zn1.04)[Cr1.94V0.06]Se4 13.970.1

The results are in % (m/m)

which is attributed to Cr3þ ions. The g-values remain constant inthe PM temperature range (Fig. 2b). In contrast, the ESR linewidth(DB) shows behaviors that are dependent on the temperatureand independent of the concentration of the chromium ions. Theplots of the temperature dependence of the ESR linewidth for:(Zn0.98Sb0.01)[Cr1.98]Se4 and (Zn0.97Sb0.02)[Cr1.99]Se4 are shownin Fig. 2(a). Starting from the T¼400 K, the linewidth decreasedas the temperature was reduced to T¼125 K. The ESR linewidth isrelated to the relaxation of the spin system. For individual spinsDB�1/t, where t is the spin relaxation time. In a dense magneticmaterial, this relationship is modified since the magnetizationrelaxes towards an effective field instead of the external field. Thetemperature dependence of the ESR linewidth for concentratedmagnetic systems at T*Tcrit has been discussed in several papersby Seehra et al. [25]. From these studies follows that the

V Cr Se

21.270.1 65.270.2

21.370.1 65.070.2

0.4270.06 20.870.3 64.670.4

0.6170.05 20.770.2 64.870.3

Fig. 2. The ESR parameters: (a) linewidth; (b) resonance field; (c) relative spin susceptibility calculated as double integration of the spectrum, as a function of the

temperature for: (Zn0.98Sb0.01)[Cr1.98]Se4 (denoted as-circles) and (Zn0.97Sb0.02)[Cr1.99]Se4 (denoted as-triangles); inset shows the relative DI�1 vs temperature.

D. Skrzypek et al. / Journal of Physics and Chemistry of Solids 72 (2011) 730–735732

temperature dependence of the linewidths outside the criticalregions associated with the magnetic transitions, arises from twomechanisms: (i) the phonon modulation of the antisymmetric(Dzialozhinsky-Moriya) exchange interaction—this behavior wasfound in [Cu(HCOO)2 �4H2O] [26] and on CuGeO3 [27]; (ii) thephonon modulation of the crystalline field—this behavior wasobserved for non S-state systems with SZ1, for exampleCrBr3 [28] and NiCl2 [29]. For ZnCr2Se4 and (Zn/Sb)Cr2Se4 spinelsthe problem of the temperature dependence of the linewidth inthe paramagnetic region is similar to that in CrBr3 [28], with S¼

3/2 for Cr3þ . The linear temperature dependence of the ESRlinewidth is observed well above TNffi20 K. From Huber andSeehra theory [28] follows that the linewidth in ZnCr2Se4 parentspinel and (Zn/Sb)Cr2Se4 doped spinels (T*TN) can be described as:

DB¼DBssþDBs-ph (1)

where DBss is described by the exchange narrowing theory [30]:

DBss¼[(DBdd)2]/Bex (2)

(i.e. is proportional to the square of the dipolar produced line-width DBdd divided by the rate of exchange) and DBs�ph repre-sents the contribution of the spin-phonon interaction.

In Ref. [28, Eq. A5] a general expression for DBs�ph is derived.From this it is apparent that a broad band of phonons takes part inthe relaxation process. This is in contrast to one-phonon relaxa-tion process of a magnetic ion, which is isolated from magneticinteractions. In this case, only narrow bands of phonons withenergies comparable to the ionic level splitting are involved inone-phonon processes. Whereas in the concentrated system, one-phonon relaxation is far more effective than it is for an isolatedion. In the latter, except at low temperatures, spin—latticerelaxation is dominated by multi-phonon processes.

3.1.2. The broadening of ESR linewidth in Zn[Cr2�xVx]Se4

The plots of the temperature dependence of the linewidth,resonance field and spectrum intensity for Zn1.06[Cr1.96V0.04]Se4

and Zn1.04[Cr1.94V0.06]Se4 are shown in Fig. 3(a), (b) and (c),respectively. The resonance spectra consist of the single Lorent-zian-shape line. The presence of V3þ ions in the ZnCr2Se4 parentspinel produces a marked broadening of the resonance linewidthin the paramagnetic phase. For Zn1.06[Cr1.96V0.04]Se4 and Zn1.04

[Cr1.94V0.06]Se4 DB¼139 mT at T¼370 K, whereas for ZnCr2Se4

DB¼42.8 mT at the same temperature (see Fig. 4). Starting fromthe T¼400 K, the linewidth values decreased as the temperaturewas reduced to T¼80 K. Deviation from linearity is observed.At temperatures above 200 K the signal became weak and verybroad, which made accurate fitting of ESR data difficult (errorabout 20%). Because of this, a monotonous shift of the resonancefield is seen in the paramagnetic region. The value of theparameter b¼DB/DT of the thermal broadening linewidth foundfor both examined compounds is bav¼0.36 mT/K and is signifi-cantly higher in comparison with b¼0.11 mT/K for the parentspinel. To understand the origin of the observed linewidth and itstemperature dependence we have to compare the relaxationproperties of the Cr3þ and V3þ ions. In the chromium spinels,the Cr3þ ions always occupy the B-site of the spinel structure. Thelocal symmetry on this octahedral site leads to a nondegenerateorbital ground state with S¼3/2. On the other hand, for the 3d2

configuration of V3þ (S¼1), the 3F free ion ground state is split byan octahedral field leaving an orbital triplet (T2) lowest. Becauseof that, Cr3þ is the ion weakly coupled to the lattice in compar-ison with the fast-relaxing V3þ ions [31]. The problem of ESRlinewidth for dilute paramagnetic admixtures in an exchange-coupled paramagnetic host has been investigated by Gulley andJaccarino [32] using the phenomenological coupled equationsof motion method. A detailed explanation of these equationsand their solutions can be found in their review. The systems

Fig. 3. The ESR parameters: (a) linewidth; (b) resonance field; (c) relative spin susceptibility calculated as double integration of the spectrum, as a function of the

temperature (inset shows the relative DI-1 vs temperature); (d) dc mass susceptibility vs temperature [23] (inset shows inverse susceptibility) for: Zn1.06[Cr1.96V0.04]Se4

(denoted as-circles) and Zn1.04[Cr1.94V0.06]Se4 (denoted as-triangles).

Fig. 4. The comparison of ESR linewidth as a function of temperature within the

paramagnetic region for: (i) ZnCr2Se4 (denoted as-circles); (ii) (Zn0.98Sb0.01)

[Cr1.98]Se4 (denoted as-triangles); (iii) Zn1.04[Cr1.94V0.06]Se4 (denoted as-squares).

δ12

δ21

δ2L

δ1L

(1) Host Zn-Cr-Se

Lattice

(2) vanadium

dopant

Fig. 5. Model of paramagnetic relaxation processes of the Zn[Cr2�xVx]Se4 spinel

systems.

D. Skrzypek et al. / Journal of Physics and Chemistry of Solids 72 (2011) 730–735 733

investigated contain three distinct components: (1) the hostZnCr2Se4 subsystem contains Cr3þ ions, (2) the admixture sub-system contains V3þ ions and (L) the lattice. Fig. 5 shows theschematic picture for such a system with arrows indicatingpossible relaxation paths between the components. The para-meters dnm (n,m¼1,2) are the spin–spin relaxation rate, resultingfrom the exchange interaction between subsystems; d1L and d2L

describe the spin–lattice relaxation rate of chromium and

vanadium ions, respectively. From the analysis in [32] the ESRlinewidth can be written as follows:

DB¼DB0þ{(wV/wCr) d21 k2 [X/(1þX)]} (3)

where: DB0 is the ESR linewidth of ZnCr2Se4 spinel; wV and wCr aremagnetic susceptibility of Zn–[Cr/V]–Se and parent spinel, respec-tively; k¼gCr/gV and X¼d2L/d21 is the bottleneck parameter.

As the parameter X increases, the bottleneck opens, the linesbroaden in proportion to d2L and relaxation of the system isdominated by the fast spin–lattice relaxation rate of the admix-ture ions. In Zn–(Cr/V)–Se investigated spinels, the introduction of

D. Skrzypek et al. / Journal of Physics and Chemistry of Solids 72 (2011) 730–735734

a third element (V3þ ions) provides an additional relaxation pathcreated by phonon modulation of the crystalline field. The line-width behavior results from the variation of the spin–latticerelaxation rate of the vanadium ions. In terms of the parametersof the equation of motion model (Eq. (3)), the strong increase oflinewidth with temperature (b¼0.36 mT/K) is consistent with aprogression from a region where d2L is slow enough (relative tod21), rendering a system that is more or less bottlenecked. For theregion where d21ffid21 a pronounced broadening is observed.

The system investigated contains two types of magnetic ions:Cr3þ and V3þ , the former is weakly coupled to the lattice incomparison with the latter. We believe that strong broadeningand temperature dependence of linewidth in PM region can bedescribed by the complex paramagnetic relaxation model. Thesubsystem exchange–coupled Cr3þ ions is coupled with lattice:(1) directly (d1L parameter and DB0 in Eq. (3) and (2)) through theadmixture subsystem containing V3þ ions. The relaxation process(1) is described with Huber–Seehra theory [28] and relaxation(2) by Gulley–Jaccarino theory [32].

3.2. The critical behavior of the electron spin resonance in

(Zn1�xSbx)[Cr2�x/3]Se4 and Zn[Cr2�xVx]Se4 spinels

The magnetic investigations of ZnCr2Se4 spinel doped with Sband V ions were carried out by some of us [21–23]. Accordingto [23] the magnetic characteristics of Sb3þ substituted systemare very similar to those of the parent compound ZnCr2Se4 andthe Neel temperature TN¼22 K. Upon incorporating vanadiumions into ZnCr2Se4, the Neel temperature decreases to 17.5 Kdetermined for the maximum V content. In Fig. 3(d) the magneticsusceptibility vs temperature data (from [23]) are shown.

The changes of ESR parameters (linewidth DB, resonance fieldBr and intensity DI obtained from the second integration of fieldderivative absorption curve—DI values were reduced to Tmax) inthe whole temperature range are illustrated in Figs. 2 and 3. As afunction of T, the ESR linewidth for all samples decreases to ashallow minimum at 60–65 K, which is above the orderingtemperature. With further temperature reduction, the broadeningof DB is observed; below T0E40 K , DB increases rapidly. Thisbehavior is accompanied by shift of the resonance field ascompared to the high-temperature value. At the same time, thespin susceptibility (DI) rapidly increases and exhibits a broadmaximum at T0, well above the ordering temperature determinedfrom magnetic susceptibility experiments [21,23]. At the tempera-ture range from 40 to 20 K the linewidth increase produces a rapiddiminution in the intensity and the spectrum is no longerobserved below 17–20 K. The observed behavior of the linewidthand resonance field is attributed to critical phenomena whileapproaching the antiferromagnetic order. The theory of the cri-tical-point anomalies in the ESR linewidth in antiferromagnetswas presented by Huber [33] and Huber and Seehra [34] whodemonstrated that the growth of DB as T-TN from the high-temperature side reflects the increase in the lifetime and thecorrelation length of the critical fluctuations. According to theprediction of this theory, anisotropy plays a fundamental role inthe nature of the anomaly observed near the Neel temperature.The ESR linewidth near TN can be written as follows:

DB�DBncrit(T)þDBcrit(T) (4)

where the factors DBncrit(T) and DBcrit(T) represent the non-critical and critical contributions to the linewidth, respectively.DBncrit(T) is also a function of temperature, see Eqs. (1) and (3).

The angular dependence of the contributions to the linewidthis interesting. However, the local symmetry of the ligandssurrounding the magnetic ion is predominantly cubic in ZnCr2Se4

and ZnCr2Se4-doped spinels and the neighboring selenium ionsform a nearly perfect octahedron. In this case, anisotropies in thelinewidth are not expected. As is evident in Figs. 2a and 3a, thetemperature dependence of ESR linewidth in the critical regioncan be fitted to the empirical relation: DB�(T–TN)g with g¼�0.7.The same result was obtained in NiCl2 by Birgeneau et al. [29].

The shift of the resonance field implies the formation ofinternal fields. The onset of the resonance field shift at aboutT¼60 K means that short range ordering of spins starts to developfrom the temperature much higher than TN. Particularly interest-ing is the temperature dependence of spin susceptibility. Themagnetic structure of ZnCr2Se4 is characterized by ferromagneticplanes with a turn angle of the spin direction of 421 betweenneighboring planes [3–6]. It is known that below TN the intensityof the resonance line is expected to decrease as a consequence ofthe development of a field-dependent energy gap in the fre-quency-field diagram. The temperature dependence of DI sug-gested that the magnetic ordering of ZnCr2Se4 doped by antimonyor vanadium ions occurs in a two-step process: during cooling,first, upto T0, a two-dimensional short-range ferromagnetic cor-relations grow in the planes of the crystals, then, at TN, theantiferromagnetic ordering between the planes appears.

4. Conclusions

The following conclusions can be drawn on ESR in(Zn1�xSbx)[Cr2�x/3]Se4 and Zn[Cr2�xVx]Se4 spinels from theresults of the experiments performed:

�

For ZnCr2Se4 diluted with antimony, the magnetic characteristiclike the ordering temperatures are nearly the same as in parentspinel. Upon incorporating vanadium ions, the Neel tempera-ture decreases down to 17.5 K, determined for the maximumV-content x¼0.06. The ESR results appear to be in reasonableagreement with the magnetic susceptibility ones. � The linear temperature dependence of ESR linewidth which is

observed for Sb3þ�doped ZnCr2Se4 shows that one-phonon

relaxation may prevail in PM materials even at high temperatures.This effect is caused by a broad band of phonons that mayparticipate in the spin relaxation process, in accordance toHuber–Seehra theory [28].

� The strong broadening and strong temperature dependence of

linewidth are observed in PM region for V3þ�doped ZnCr2Se4,

in comparison with DB for parent spinel. These effects areexplained by the complex paramagnetic relaxation model.

� The ESR data in critical temperature region suggested that the

magnetic ordering of ZnCr2Se4 doped by antimony or vana-dium ions occurs in a two-step process.

References

[1] P.K. Baltzer, P.J. Wojtowicz, M. Robbins, E. Lopatin, Phys. Rev. 151 (1966) 357–377.[2] E.K. Lothering, Solid State Commun. 3 (1965) 347.[3] K. Dwight, N. Menyuk, Phys. Rev. 163 (1967) 435–443.[4] K. Siratori, J. Phys. Soc. Jpn. 30 (1971) 709–719.[5] R. Plumier, M. Lecomte, A. Miedan-Gros, M. Sougi, Phys. Lett. A 55 (1975) 239.[6] J. Akimitsu, K. Siratori, G. Shirane, M. Iizumi, T. Watanabe, J. Phys. Soc. Jpn. 44

(1978) 172–180.[7] J. Watanabe, S. Endo, A. Kasai, Jpn. J. Appl. Phys. 19 (3) (1980) 279.[8] H.W. Lehmann, M. Robbins, J. Appl. Phys. 37 (1966) 1389–1390.[9] J. Tang, T. Matsumoto, T. Naka, T. Furubayashi, S. Nagata, N. Matsumoto,

Physica B 259-261 (1999) 859.[10] J. Hemberger, H.-A. Krug von Nidda, V. Tsurkan, A. Loidl, Phys. Rev. Lett. 98

(2007) 147203-1-4.[11] T. Rudolf, Ch. Kant, F. Mayr, J. Hemberger, V. Tsurkan, A. Loidl, Phys. Rev. B 75

(2007) 052410-1-4.[12] M. Hidaka, M. Yoshimura, N. Tokiwa, J. Akimitsu, Yong Jun Park, Jae

Hyun Park, Sung Dae Ji, Ki Bong Lee, Phys. Status Solidi (b) 236 (2003)9–18 209–218; 570–577.

D. Skrzypek et al. / Journal of Physics and Chemistry of Solids 72 (2011) 730–735 735

[13] J. Krok-Kowalski, J. Warczewski, T. Mydlarz, A. Pacyna, A. Bombik,J. Kopyczok, I. Okonska-Kozlowska, J. Magn. Magn. Mater. 111 (1992) 50–52.

[14] T. Gron, Philos. Mag. B 70 (1994) 121–132.[15] S. Juszczyk, J. Krok-Kowalski, I. Okonska-Kozlowska, T. Mydlarz, A. Gilewski,

J. Magn. Magn. Mater. 46 (1984) 105–113.[16] I. Okonska-Kozlowska, E. Malicka, A. Waskowska, T. Mydlarz, J. Solid State

Chem. 148 (1999) 215–219.[17] T. Gron, H. Duda, J. Warczewski, Phys. Rev. B 41 (1990) 12424–12431.[18] T. Gron, E. Malicka, I. Okonska-Koz"owska, A. Waskowska, Ferrites: Proceedings

of the Eight International Conference on Ferrites, Kyoto and Tokyo, 2000, p. 211.[19] E. Malicka, A. Waskowska, T. Mydlarz, D. Kaczorowski, J. Alloys Compd. 440

(2007) 1–5.[20] D. Skrzypek, E. Malicka, A. Waskowska, A. Cichon, J. Crys. Growth 312 (2010)

471–477.[21] E. Malicka, A. Waskowska, J. Heimann, T. Mydlarz, R. Sitko, D. Kaczorowski, J.

Solid State Chem. 181 (2008) 1970–1976.[22] E. Malicka, T. Gron, H. Duda, A.W. Pacyna, J. Krok-Kowalski, Acta Phys. Pol. A

116 (2009) 964–966.

[23] H. Duda, E. Malicka, T. Gron, A.W. Pacyna, J. Kusz, Acta Phys. Pol. A 116 (2009)962–963.

[24] R. Sitko, B. Zawisza, E. Malicka, Spectrochim. Acta B 64 (2009) 436–441.[25] M.S. Seehra, M.M. Ibrahim, V.S. Babu, G. Srinivasan, J. Phys.: Condens. Matter

8 (1996) 11283–11289.[26] T.G. Castner, M.S. Seehra, Phys. Rev. B 4 (1971) 38.[27] I. Yamada, M. Nishi, J. Akimisu, J. Phys.: Condens. Matter 8 (1996)

2625.[28] D.L. Huber, M.S. Seehra, J. Phys. Chem. Solids 36 (1975) 723–725.[29] R.J. Birgeneau, L. Rupp, H.J. Guggenheim, P.A. Lindgard, D.L. Huber, Phys. Rev.

Lett. 30 (1972) 1252.[30] A. Abragam, B. Bleaney, Electron paramagnetic resonance of transition ions,

Clarendon Press, Oxford, 1970.[31] C.A. Bates, A. Gavaix, P. Steggles, A. Vasson, A.M. Vasson, J. Phys. C: Solid State

Phys. 9 (1976) 2413.[32] J.E. Gulley, V. Jaccarino, Phys. Rev. B 6 (1972) 58.[33] D.L. Huber, Phys. Rev. B 6 (1972) 3180–3186.[34] D.L. Huber, M.S. Seehra, Phys. Status Solidi (b) 74 (1976) 145.