II Materials Chalcospinels Delafossite oxides Dilute oxide - - PowerPoint PPT Presentation

MANSE Midterm Review

II Materials

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

MANSE Midterm Review

Staff, Publications

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

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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)

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— 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)

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— 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)

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Characterization

• X-ray/Neutron diffraction
• SEM/EDAX/RBS/AFM/MFM/HRTEM
• SQUID magnetometry
• Optical spectrometry
• XAS/XES/XMCD
• Transport measurements

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• I. Chalcospinels

Chalcospinels Normal cubic spinel structure. n-type magnetic semiconductors CuCr2S4 TC = 420 K 4.6 µB/f.u CuCr2Se4 TC = 460 K 4.9 µB/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).

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CuCr2Se4 ceramic

Prepared at 550° C (below peritectic transition)

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High temperature synthesis

5.2 850 5.5 750 6.0 550 σ (µB) @5K Temp (°C)

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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

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Magnetizaton

Before Annealing After Annealing Films from metallic target Polycrystalline samples, mixed phases

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CuCr2Se4-xBrx

Powders Powders

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

550 C. It is probably a half-metal.

Single crystals Single crystals

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

Thin films Thin films

• ~ Single phase after annealing

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Next steps

• Complete torque curves

Complete torque curves

• Low

Low-

• temperature heat capacity

temperature heat capacity

• IR optical conductivity (with

IR optical conductivity (with Dimitri Dimitri Basov, UCSD) Basov, UCSD)

• Thermal conductivity

Thermal conductivity

• Neutron diffraction (LLB April)

Neutron diffraction (LLB April)

• Andreev reflection

Andreev reflection

• AC Squid

AC Squid magnetometry magnetometry; Sensitivity 3 10 ; Sensitivity 3 10-

• 15

15 A m

A m2

2 for

for dc fields < 1 T. dc fields < 1 T. If the mobility permits, demonstrate an all-ferromagnetic transistor.

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• II. Delafossite oxides

CuAlO2 CuCrO2:Ca,Mg CuInO2: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.

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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 V/K at 300K 50% transparent to visible light (250 nm thick film)

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0.1 1 10 100 1000 450 500 550 600 650 700 750 800 H2201CCO H2301CCO H2401CCO H2501CCO H2701CCO H2801CCO H2901CCO2 H2901CCO H2801CCO2 Cu2O CuCrO2 CuO, CuCr2O4 Cu2O CuCrO2 CuCr2O4 Amorphous Cu2O Amorphous

C u C r O 2

T (

• C)

PO2 (µ

µ µ µbar)

10% 5% 2% Undoped Mg Doping 10 kΩ 40 2 1.5 650 20 H2103CCMO 600 kΩ 31 1 1.5 650 20 H1703CCMO 5 MΩ 20 2 1.0 650 10 H0502CCMO ∞ 63 5 1.9 700 10 H2301CCO Conductivity (2 probe) Thickness (nm) Rep Rate (Hz) Fluence (J/cm2) T (oC) P (μbar)

• 10

20 30 40 50 60 70 80 90 100 110 120

(003) (006) (101) (009) (0012) (202) (0018) (003) (006) (009) (0012) (0018) (101) (202) (003) (006) (009) (0012) (0018) (101) (202) (003) (006) (009) (0012) (0018) (101) (202)

Intensity (arb. units) 2θ (deg)

H2301CCO

Cu

H0502CCM O

Cu2O (111)

H1703C CMO

Cu

H2103CCMO

10% Mg 5% Mg 2% Mg Undoped

PLD films

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50 100 150 200 250 300 0.00 0.01 0.02 0.03 0.04 0.05 0.06

10 20 30 40 50 60 70 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

ρ (Ωcm)

T (K)

H2103CCMO

ln(σ) (Scm

• 1)

1000/T (K

• 1)

10% Mg

20 25 30 35 40 45 50 1 10 100 1000 10000 100000 (006) CuCrO2 (009) CuCrO2 (101) CuCrO2 (002) ZnO

Intensity (C) 2θ (deg)

H2611ZCO_6

*

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

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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

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• 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 γ = 5 mJ mol-1K-2 properties depend on oxygen stoichiometry LSTO nanoparticle system

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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 diffraction SEM/EDAX TEM SQUID magnetometry Mössbauer spectrometry

Nanoparticle synthesis

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(La0.5Sr0.5)TiO3:Undoped

• 5
• 4
• 3
• 2
• 1

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 18/09/07 300 K Gel cap I 29.5 mg Gel cap II 29.3 mg Moment (10

• 3 Am

2)

µ0H (T)

• 4
• 2

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 Moment (10

• 3 Am

2)

µ0H (T)

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

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Magnetization

• 5
• 4
• 3
• 2
• 1

1 2 3 4 5

• 2.0
• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 2.0

Moment (10

• 6 Am

2)

µoH (T)

LSTO nanoparticles LSTO bulk

Nanocrystalline χdia = -4.1 10-9 m3 kg-1 Ceramic χdia = -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.

50 100 150 200 250 300

• 24
• 20
• 16
• 12
• 8
• 4

Temperature (K) Moment (10

• 8Am

2)

Gel cap LSTO nanoparticles + Gel cap LSTO nanoparticles LSTO ceramic

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TM: LSTO

• 4
• 2

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 Moment (Am

2kg

• 1)

µ0H (T)

Sc Ti V Cr Mn Fe Co Ni 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Ferromagnetic Paramagnetic

Magnetic moment Transition metal

• 4
• 2

2 4 92 94 96 98 100

Transmission (%) Velocity (mm s

• 1)
• 10 -8
• 6
• 4
• 2

2 4 6 8 10 95 96 97 98 99 100

Transmission (%) Velocity (mm s

• 1)

Raw Fit Fe

3+

Fe

2+

Fe

3+

Fe

Fe:LSTO Ceramic Fe:LSTO Nanocrystalline Co:LSTO 2% Co

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The nanocrystalline samples doped with the late transition elements 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

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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

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

Characterization

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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

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5%Co-doped ZnO nanorods Hydrothermal, Zn acetate, Co acetate, NaOH, 120° C for 12h

ZnO nanorods

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Summary

In 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 (αFe 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.

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• 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

5 10 15

m (10

• 8Am

2)

µ0H (T)

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

0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2

R-cut C-cut Moment (µB/Co) Al content (at.%)

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1 2 3 4 5 20 40 60 80 100 Transmission (%) Energy (eV)

0.0 % Al

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

20 40 60 80 100 0.1 1 10 100

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 Carrier concentration n x 10

• 3

Al nominal concentration, %

Hall Resistance RH, Ω/T Temperature T, K

Band gap widening

0.01 0.1 1 10 0.01 0.1 1

∆Eg (eV) nHall x 10

20 (cm

• 3)

ZnCoAlO γ = 0.66(5) γ = 0.33 m* = 0.26(3) me

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)

90 180 270 360 41.0 41.5 42.0 42.5 43.0 Resistance R, kΩ Angle θ, deg

Conductance coeficient σ2, x 10

• 6 S

Temperature T, K

2 2 2/3

(3 ) 2 *

g e

E n m π ∆ =

1 1 1 *

e h

m m m = +

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2 4 6 8 10 12 14 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Conductance Coefficient σ2, S Magnetic Field µ0H, T 257ZCAl2 (1% Al) T = 2 K T = 5 K T = 10 K T = 20 K T = 50 K

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

Conductance Coefficient σ2, S x 10

6

Magnetic Field µ0H, T

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

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50 100 150 200 250 300 20 40 60 80 100

Data Exponential Fit

Data: Temp_F Model: ExpDec1 Chi^2/DoF = 2143.51872 R^2 = 0.98547 y0 3.3 ±2.6 mT A1 85.7 ±3.8 mT t1 19.5 ±2.9 K

Coercive Field Hc, mT Temperature T, K

0.0 0.1 0.2 0.3 0.4 0.5 0.6 2.0x10

• 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

Saturating Moment ms, Am

2

Inverse Temperature 1/T, 1/K Saturating Moment Linear Fit of Temp_D A = 3.5(3) 10

• 8 Am

2

B = 1.2(1) 10

• 7 Am

2K/5T

• 5
• 4
• 3
• 2
• 1

1 2 3 4 5

• 1.0x10
• 7
• 5.0x10
• 8

0.0 5.0x10

• 8

1.0x10

• 7

ZnCoO: 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

Corrected Magnetic Moment mc, Am

2

Magnetic Field µ0H, T

• 1.00
• 0.75
• 0.50
• 0.25

0.00 0.25 0.50 0.75 1.00

• 2x10
• 7
• 1x10
• 7
• 5x10
• 8

5x10

• 8

1x10

• 7

2x10

• 7

T = 1.8 K T = 300 K Magnetic Moment m, Am

2

Magnetic Field µ0H, T

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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

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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

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Future work

Chalcogenides

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 oxides

Make all-oxide heterostructures; pn junctions and pnp stacks.

Dilute Oxides

Search for new and novel dilute magnetic oxides by suitable cation doping.

Nanoparticle systems

Understanding of defects, interface magnetism and detailed theoretical calculations.

Heusler alloys

Exploit high Curie temperature Heusler alloys Co2MnSi, Co2FeSi etc.

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Outline

Background TiO2:Fe ☺ Magnetic silicon

• Graphite
• Anthracene
• MgO:N

☺ Au nanoparticles ☺ A model — Charge-transfer ferromagnetism