MANSE Midterm Review II Materials Chalcospinels Delafossite oxides Dilute oxide nanoparticles Al-doped Co:ZnO thin films Future work

MANSE Midterm Review

II Materials

Chalcospinels Delafossite oxides Dilute oxide nanoparticles Al-doped Co:ZnO thin films Future work


Staff, Publications

• M Venkatesan Senior postdoc• Karsten Rode Postdoc• Delphine Lebeugle Postdoc• Jonathan Alaria Postgrad• Marita O’Sullivan Postgrad• Simone Alborgetti Postgrad


Publications:—Oxide dilute magnetic semicondutors – Fact or Fiction? J.M.D. Coey, S.A. Chambers, MRS Bulletin 33 1063-8 (2009)—Dilute magnetic oxides and nitrides, K. Rode and J. M. D. Coey, in Handbook of Magnetism and Advanced Magnetic Materials (H Kronmullar and S Parkin, editors), Vol 4, pp 2107 – 2121 (2007)—Dilute magnetic oxides, J. M. D. Coey, Comments on Solid State and Materials Sciences 10 83-92 (2007)

—Magnetism in dilute magnetic oxide thin films based on SnO2, C. B. Fitzgerald, M. Venkatesan, L. S. Dorneles, R. Gunning, P. Stamenov, J. M. D. Coey, P. A. Stampe, R. J. Kennedy, E. C. Moreira and U. S. Sias, Physical Review B, 74, 115307 (2006)

— Giant moment and magnetic anisotropy in Co-doped ZnO films grown by pulse-injection metal organic chemical vapor deposition, A. Zukova, A. Teiserskis, S. van Dijken, Y. K. Gun’ko and V. Kazlauskiene, Applied Physics Letters, 89, 232503 (2006)

— Charge-transfer ferromagnetism in oxide nanoparticles, JMD Coey, Kwanruthai Wongsaprom, J. Alaria and M. Venkatesan, Journal of Physics D: Applied Physics, 41, 134012 (2008)

— Magnetic, magnetotransport and optical properties of Al-doped Co-doped ZnO thin films M. Venkatesan, P. Stamenov, L. S. Dorneles, R. D. Gunning and J. M. D. Coey, Applied Physics Letters 90 242508 (2007)

—Magnetic and structural properties of Co-doped ZnO thin films, L.S. Dorneles, M. Venkatesan, R. Gunning, P. Stamenov. J. Alaria, M. Rooney, J.G. Lunney, J.M.D. Coey, Journal of Magnetism and Magnetic Materials 310 2087-2088 (2007)


— Room temperature ferromagnetism in Mn- and Fe-doped indium tin oxide thin films, M. Venkatesan, R.D. Gunning, P. Stamenov, J.M.D. Coey, Journal of Applied Physics, 103, 07D135 (2008)— Structural and magnetic properties of wurzite CoO thin films, J. Alaria, N. Cheval, K. Rode, M. Venkatesan and J.M.D. Coey, Journal of Physics D: Applied Physics, 41, 135004 (2008) — Magnetism of ZnO nanoparticles doped with 3d cations prepared by a solvothermal Method, J. Alaria, M.Venkatesan and J.M.D. Coey, Journal of Applied Physics 103 07D123 (2008)—Magnetism’s ticklish giant, Nature Materials 5 677-8 (2006)

—Magnetic properties of CNx whiskers. R. D. Gunning, M. Venkatesan, D. H. Grayson and J. M. D. Coey, Carbon, 44 3213-7 (2006)—The origin of Magnetism of etched silicon. P. Grace, M. Venkatesan, J. Alaria and J.M.D. Coey, Advanced Materials (in press)—Absence of toroidal moments in aromagnetic anthracene. S. Alborghetti, E. Puppin, M. Brenna, E. Pinotti, P. Zanni, J.M.D. Coey, New Journal of Physics 10 063019 (2008)—Thin films of semiconducting lithium ferrite produced by pulsed laser deposition, R.D. Gunning, Karsten Rode, Sumesh R.G. Sophin, M. Venkatesan, JMD Coey, Igor V. Shvets, Applied Surface Science (in press) —Half-metallic Ferromagnets, M. Venkatesan, in Handbook of Magnetism and Advanced Magnetic Materials (H Kronmullar and S Parkin, editors), Vol 4, pp 2133 – 2156 (2007)


— Ferromagnetic nanoparticles with strong surface anisotropy: Spin structures and magnetisation processes, L. Berger, Y. Labaye, M. Tamine, J.M.D. Coey, Physical Review B 77 104431 (2008)

— Magnetic anisotropy of ilmenite-hematite solid solution thin films grown by pulsed laser ablation, K. Rode, R.D. Gunning, R.G.S. Sofin, M. Venkatesan, J.G. Lunney, J.M.D. Coey and I.V. Shvets, Journal of Magnetism and Magnetic Materials, 320, 3238 (2008)

—Permanent Magnets, T. Ni Mhiochain and J. M. D. Coey, Encyclopedia of Life Support Systems Volume 3: Physical methods, instruments and measurements, Y. M. Tsipenyuk (editor),.Chapter 10 pp 203 – 258 EOLSS/UNESCO Paris (2007)


Characterization

• X-ray/Neutron diffraction

• SEM/EDAX/RBS/AFM/MFM/HRTEM

• SQUID magnetometry

• Optical spectrometry

• XAS/XES/XMCD

• Transport measurements


I. ChalcospinelsChalcospinels

Normal cubic spinel structure. n-type magnetic semiconductors

CuCr2S4 TC = 420 K 4.6 B/f.u CuCr2Se4 TC = 460 K 4.9 B/f.u CdCr2Se4 TC = 130 K

Conduction electrons may be fully spin polarized - potential half-metal?

A red shift (0.05 eV) of the absorption edge on passing the TC.High room temperature magneto-optical Kerr effect (1.2º at 0.9 eV).


CuCr2Se4 ceramicPrepared at 550°C (below peritectic transition)


High temperature synthesis

Temp (°C) (B) @5K

550 6.0

750 5.5

850 5.2


PLD films

Deposition conditions

Ceramic target

Substrate c-Al2O3, MgO, MgAl2O4, RT-700°C

1 J/cm2 5Hz

Pressure ~ 10-6 mbar

Metallic target

Substrate MgO 200°C

1 J/cm2 5Hz

Pressure ~10-6 mbar

Annealing process

500°C in Se Vapour (from elemental Se powder) in a vacuum sealed quartz tube for 48 hours

Growth of CuCr2Se4 thin films from ceramic target


Magnetizaton

Before Annealing After Annealing

Films from metallic target

Polycrystalline samples, mixed phases


CuCr2Se4-xBrx

PowdersPowders• Synthesis temperature is critical.• Saturation magnetic moment of 6 B/mol can be achieved in CuCr2Se4 made at

550 C. It is probably a half-metal. Single crystalsSingle crystals

• Metallic (CuCr2Se4) or intrinsic semiconductor (CdCr2Se4) when undoped• Anomalous Hall effect and AMR

Thin filmsThin films• ~ Single phase after annealing


Next steps Complete torque curvesComplete torque curves Low-temperature heat capacityLow-temperature heat capacity IR optical conductivity (with Dimitri Basov, UCSD)IR optical conductivity (with Dimitri Basov, UCSD) Thermal conductivityThermal conductivity Neutron diffraction (LLB April)Neutron diffraction (LLB April) Andreev reflectionAndreev reflection AC Squid magnetometry; Sensitivity 3 10AC Squid magnetometry; Sensitivity 3 10-15 -15 A mA m2 2 for for

dc fields < 1 T. dc fields < 1 T.

If the mobility permits, demonstrate an all-ferromagnetic transistor.


II. Delafossite oxides

CuAlO2

CuCrO2:Ca,MgCuInO2:Mg,Sn

Carrier density and mobility are the major factors that require to be improved.

Cu-delafossite is still considered to be a potential p-type semiconductor for transparent electronics.


CuCrO2

CuCrO2

p-type transparent conducting oxide (TCO)

Delafossite structure: A1+B3+O2

Crystal system: Rhombohedral

Space group: R-3m

Lattice parameters: a = 2.9761(2) Å, c = 17.102(1) Å

Bandgap: 3.2 eV

Antiferromagnetic: TN = 25K

Mg-doped CuCrO2

High conductivity for p-type TCO: 220 S/cm (5% Mg)

Thermopower +153 μV/K at 300K 50% transparent to visible light (250 nm thick film)


Mg Doping P (μbar) T (oC) Fluence (J/cm2)

Rep Rate (Hz)

Thickness (nm)

Conductivity (2 probe)

H2301CCO Undoped 10 700 1.9 5 63 ∞

H0502CCMO 2% 10 650 1.0 2 20 5 MΩ

H1703CCMO 5% 20 650 1.5 1 31 600 kΩ

H2103CCMO 10% 20 650 1.5 2 40 10 kΩ

Growth Conditions

10% Mg

5% Mg

2% Mg

Undoped

PLD films


10% Mg 10% Mg-CuCrO2/0.1% Al-ZnO/(0001)/Al2O3


Growth of highly-crystalline native p-type delafossite oxide films CuCrO2, CuAlO2

Good quality n-type Al:ZnO films are also grown by PLD (mobility ~ 20 cm2 V-1 s)

Next steps: Make all-oxide heterostructures; pn junctions and pnp stacks. Use sapphire shadow masks.

Summary


III. Dilute oxide nanoparticles

Systematic investigation of the magnetic properties of LSTO, undoped and with transition metal doping (substitution for Ti at the 1.5 or 2.0 % level) for dopants ranging from Sc to Ni.

Tokura et al, PRL 1988

spd-band metal.

0.5 electrons per formula

= 5 mJ mol-1K-2

properties depend on oxygen stoichiometry

LSTO nanoparticle system


Polymerized complex method, using Ti isopropoxide and nitrate precursors

Bulk ceramic samples of undoped LSTO, and LSTO with 2 % 57Fe doping were made by mixing and firing the components at 1000 C.

The pellet was placed in a ceramic boat and sintered at 1150 C for 24 h in air or flowing argon.

The nominal purity of the starting materials was 99.99 % or better.

X-ray diffractionSEM/EDAXTEMSQUID magnetometryMössbauer spectrometry

Nanoparticle synthesis


(La0.5Sr0.5)TiO3:Undoped

-5 -4 -3 -2 -1 0 1 2 3 4 5-0.0010

-0.0008

-0.0006

-0.0004

-0.0002

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

Gel cap I Gel cap II

18/09/07300 K

Gel cap I 29.5 mgGel cap II 29.3 mg

Mom

ent

(10-3

Am

2 )

0H (T)

-4 -2 0 2 4-0.0025

-0.0020

-0.0015

-0.0010

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025 300 K 20 K 10 K 5 K 4 K 2 K

28/09/07

LSTO TCD 65.0 mg Gel cap: 29.0 mg

Mom

ent (

10-3 A

m2 )

0H (T)

Paramagnetism due to S = 1/2 defects in the LSTO particles


Magnetization

-5 -4 -3 -2 -1 0 1 2 3 4 5-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Mom

ent (

10-6

Am

2 )

oH (T)

LSTO nanoparticles LSTO bulk

Nanocrystalline dia = -4.1 10-9 m3 kg-1 Ceramic dia = -1.2 10-9 m3 kg-1

The ceramics show a diamagnetic susceptibility that is smaller by a factor of three than that of the nanoparticles.

0 50 100 150 200 250 300-24

-20

-16

-12

-8

-4

0

Temperature (K)M

omen

t (10

-8A

m2 )

Gel cap LSTO nanoparticles + Gel cap LSTO nanoparticles LSTO ceramic


TM: LSTO

-4 -2 0 2 4-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

300 K 200 K 100 K 50 K 4 K

Co2% LSTO 18.5 mg

Mo

me

nt (

Am

2 kg-1)

0H (T)

Sc Ti V Cr Mn Fe Co Ni0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0 Ferromagnetic Paramagnetic

Mag

netic

mom

ent

Transition metal

-4 -2 0 2 492

94

96

98

100

Tra

nsm

issi

on (

%)

Velocity (mm s-1)

-10 -8 -6 -4 -2 0 2 4 6 8 1095

96

97

98

99

100

Tra

nsm

issi

on (

%)

Velocity (mm s-1)

Raw Fit

Fe3+

Fe2+

Fe3+

Fe

Fe:LSTO Ceramic

Fe:LSTO Nanocrystalline

Co:LSTO2% Co


The nanocrystalline samples doped with the late transitionelements Fe, Co and Ni behave differently.

In addition to a temperature-dependent, Curie-Weiss term in the susceptibility, they all show a nonlinear, ferromagnetic-like component in their magnetization curves

The samples doped with cations from Sc – Mn all exhibit linear magnetization curves and a Curie-Weiss susceptibility

LSTO summary


Phys Rev B 2007 Many oxide nanoparticles exhibit a tiny magnetization < 0.1 A m2 kg-1

ZnO: 5% M = Sc - Cu

TM: ZnO nanoparticles

Solvo-/hydrothermal technique


All the samples prepared in series A, except for TM=Ni, are diamagnetic or paramagneticas expected for the dilution of the TM in the ZnO matrix.

Characterization


Mössbauer spectra

Sample B

70% of the iron is a similar +3 state. However, 30% of the iron appears in a magnetically order form, identified from the spectrum as magnetite and hematite.

Sample A

No magnetic ordering of the iron, Fe3+, with an isomer shift of 0.37 mm s-1 relative to α-Fe, and a quadrupole splitting of 0.46 mm s-1, as expected for substituted Fe3+ on tetrahedral site in ZnO.A

B


5%Co-doped ZnO nanorods

Hydrothermal, Zn acetate, Co acetate, NaOH,

120°C for 12h

ZnO nanorods


SummaryIn two nanoparticle systems — ZnO;M and LSTO;M the TM dopants are usually paramagnetic. Ferromagnetic moments only apperar in some sample when M = Fe, Co or Ni.

Where it was possible to analyse the iron phases specifically, using Mossbauer spectroscopy, evidence of a ferromagnetic secondary phase (Fe or Fe3O4) was found.

It is likely that much or all of the ferromagnetism in these materials can be explained by ferromagnetic secondary phases.

The origin of the room temperature ferromagnetism in the Fe and Ni doped ZnO prepared with a non-homogeneous precursor is explained by the presence of a secondary phase magnetite and metallic Ni, respectively.

The evidence indicates that room temperature ferromagnetism in these doped ZnO nanoparticles has an extrinsic origin.


IV. Al-doped Co:ZnO films

Zn0.95Co0.05O + x at.% Al

x = 0.1, 0.2, 0.5, 0.7 and 1 at.% Al

-1.0 -0.5 0.0 0.5 1.0-15

-10

-5

0

5

10

15

m (

10-8A

m2 )

0H (T)

Zn0.95Co0.05O 450C 6 min. 10 Hz C-Al2O3

Zn0.95Co0.05O + 0.2% Al 450C 6 min. 10 Hz C-Al2O3

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

1.2

R-cut C-cut

Mo

me

nt ( B

/Co

)

Al content (at.%)


0 1 2 3 4 50

20

40

60

80

100

Tra

nsm

issi

on

(%

)

Energy (eV)

0.0 % Al 0.1% Al 0.2% Al 0.5% Al 0.7% Al 1.0% Al Eg

0 20 40 60 80 1000.1

1

10

100

0 0.001 0.002 0.005 0.01

0.0 0.2 0.4 0.6 0.8 1.0

0.01

0.1

1

T = 100 K

Ca

rrie

r co

nce

ntr

atio

n n

x 1

020 ,

cm-3

Al nominal concentration, %

Ha

ll R

esi

sta

nce

RH,

/T

Temperature T, K

Band gap widening

0.01 0.1 1 10

0.01

0.1

1

Eg

(eV

)

nHall

x 1020 (cm-3)

ZnCoAlO = 0.66(5) = 0.33

m* = 0.26(3) me 0 5 10 15 20 25 30 35 40

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

(b)

(a)

0 90 180 270 36041.0

41.5

42.0

42.5

43.0

Res

ista

nce

R,

kAngle , deg

Con

duct

ance

coe

ficie

nt 2,

x 1

0-6 S

Temperature T, K

22 2/3(3 )

2 *g eE nm

1 1 1

* e hm m m


0 2 4 6 8 10 12 140.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Co

nd

uct

an

ce C

oe

ffic

ien

t 2,

S

Magnetic Field 0H, T

257ZCAl2 (1% Al) T = 2 K T = 5 K T = 10 K T = 20 K T = 50 K

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

Con

duct

ance

Coe

ffici

ent

2, S

x 1

06


236ZCAl2 (0.2% Al) T = 2 K T = 5 K T = 10 K T = 20 K T = 50 K


0 50 100 150 200 250 3000

20

40

60

80

100

Data Exponential Fit

Data: Temp_FModel: ExpDec1 Chi^2/DoF = 2143.51872R^2 = 0.98547 y0 3.3 ±2.6 mTA1 85.7 ±3.8 mTt1 19.5 ±2.9 K

Coe

rciv

e F

ield

Hc,

mT

Temperature T, K

0.0 0.1 0.2 0.3 0.4 0.5 0.62.0x10-8

3.0x10-8

4.0x10-8

5.0x10-8

6.0x10-8

7.0x10-8

8.0x10-8

9.0x10-8

1.0x10-7

Sat

urat

ing

Mom

ent m

s, A

m2

Inverse Temperature 1/T, 1/K

Saturating Moment Linear Fit of Temp_D

A = 3.5(3) 10-8 Am2

B = 1.2(1) 10-7 Am2K/5T

-5 -4 -3 -2 -1 0 1 2 3 4 5-1.0x10-7

-5.0x10-8

0.0

5.0x10-8

1.0x10-7ZnCoO: 214ZC502

1.8 K 2.0 K 3.0 K 4.0 K 5.0 K 10 K 20 K 50 K 100 K 200 K 300 K

Co

rre

cte

d M

ag

ne

tic M

om

en

t mc,

Am

2


-1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00-2x10-7

-1x10-7

-5x10-8

0

5x10-8

1x10-7

2x10-7

T = 1.8 K T = 300 K

Ma

gn

etic

Mo

me

nt m

, Am

2



Larger moments for films on C-cut substrates compared to R-cut substrates.

Magnetic moment decreases with increasing Al content.

Conductivity is enhanced significantly in films with low Al doping (0.1-0.2 %), maintaining the magnetic moment.

Band-gap shift (~ 0.5 eV), is observed with Al-doping.

Summary


Symposium on dilute magnetic oxides

Detailed electronic structure calculations with theorists in TCD

- LDA and spin transport calculations - Stefano Sanvito’s group - Electronic structure of oxides - Charles Patterson’s group

Dopants and defects control magnetic properties

- X-ray magnetic circular dichroism (ISRF, Grenoble)- XAS and XES (Cormac McGuinness) - Transmission electron microscopy (Peter Nellist)

Collaboration

Collaboration within SFI


Future workChalcogenides

Detailed characterization on chalcogenide systems (Neutron, Andreev etc.) and synthesis of single crystals

Materials developed will continue to be exploited for applications in MANSE.

Delafossite oxidesMake all-oxide heterostructures; pn junctions and pnp stacks.

Dilute OxidesSearch for new and novel dilute magnetic oxides by suitable

cation doping.

Nanoparticle systemsUnderstanding of defects, interface magnetism and detailed

theoretical calculations.

Heusler alloysExploit high Curie temperature Heusler alloys Co2MnSi, Co2FeSi etc.


Outline

Background

TiO2:Fe

Magnetic silicon

Graphite

Anthracene

MgO:N

Au nanoparticles

A model — Charge-transfer ferromagnetism

Documents

MANSE Midterm Review II Materials Chalcospinels Delafossite oxides Dilute oxide nanoparticles Al-doped Co:ZnO thin films Future work