II Materials


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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
MANSE Midterm Review
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 pulseinjection 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 MagneticMANSE
Materials
310
2087-2088 (2007)
Midterm
Review
— 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)
MANSE Midterm Review
— 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)
MANSE Midterm Review
Characterization
• X-ray/Neutron diffraction
• SEM/EDAX/RBS/AFM/MFM/HRTEM
• SQUID magnetometry
• Optical spectrometry
• XAS/XES/XMCD
• Transport measurements
MANSE Midterm Review
I. Chalcospinels
Chalcospinels
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).
MANSE Midterm Review
CuCr2Se4 ceramic
Prepared at 550°C (below peritectic transition)
MANSE Midterm Review
High temperature synthesis
Temp (°C)
 (B) @5K
550
6.0
750
5.5
850
5.2
MANSE Midterm Review
PLD films
Deposition conditions
Growth of CuCr2Se4 thin films from ceramic target
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
MANSE Midterm Review
Magnetizaton
Before Annealing
After Annealing
Films from metallic target
Polycrystalline samples, mixed phases
MANSE Midterm Review
CuCr2Se4-xBrx
Powders
• 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 crystals
• Metallic (CuCr2Se4) or intrinsic semiconductor (CdCr2Se4) when undoped
• Anomalous Hall effect and AMR
Thin films
• ~ Single phase after annealing
MANSE Midterm Review
Next steps
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Complete torque curves
Low-temperature heat capacity
IR optical conductivity (with Dimitri Basov, UCSD)
Thermal conductivity
Neutron diffraction (LLB April)
Andreev reflection
AC Squid magnetometry; Sensitivity 3 10-15 A m2 for
dc fields < 1 T.
If the mobility permits, demonstrate an all-ferromagnetic
transistor.
MANSE Midterm Review
II. Delafossite oxides
Cu-delafossite is still considered to be a potential p-type
semiconductor for transparent electronics.
CuAlO2
CuCrO2:Ca,Mg
CuInO2:Mg,Sn
Carrier density and mobility are the major factors that
require to be improved.
MANSE Midterm Review
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)
MANSE Midterm Review
PLD films
500
10
20
30
(202)
(0018)
(202)
(202)
(0018)
(0012)
H2301CCO
(0018)
(202)
Undoped
H0502CCMO
(0012)
(009)
(101)
2
CO
1C hous
0
9
H2 morp
A
(003)
550
(0018)
(0012)
(0012)
(009)
(003)
(101)
Cu2O (220)
O
CC
901 O
2
H u2
C
2
CO
1C hous
0
8
H2 morp
A
2% Mg
(006)
CO
1C O4
0
8
H2 uCr2
C
(006)
600
CO
1C 2
0
7
H2 uCrO
C
(009)
o
CO
1C
0
5
H2 u2O
C
H1703CCMO
(101)
Cu2O (111)
O2
Cr
u
C
650
T ( C)
5% Mg
(003)
700
CO O4
1C uCr2
0
4
H2 uO, C
C
CO
1C 2
0
3
H2 uCrO
C
Intensity (arb. units)
CO
1C
0
2
H2 u2O
C
H2103CCMO
(006)
750
(009)
(003)
10% Mg
(101)
Cu2O (111)
(006)
800
40
50
60
70
80
90
100
2 (deg)
450
0.1
1
10
100
1000
P (bar)
Growth Conditions
O2
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
MANSE Midterm Review
110
120
10% Mg-CuCrO2/0.1% Al-ZnO/(0001)/Al2O3
10% Mg
0.06
6.0
100000
10000
4.5
4.0
 (cm)
3.5
0.03
3.0
2.5
0.02
0
10
20
30
40
50
60
70
Intensity (C)
0.04
(006) CuCrO2
-1
ln() (Scm )
5.0
*
1000
(009) CuCrO2
0.05
H2611ZCO_6
(002) ZnO
(101) CuCrO2
5.5
100
-1
1000/T (K )
10
0.01
1
0.00
H2103CCMO
0
50
100
150
200
250
300
20
T (K)
MANSE Midterm Review
25
30
35
2 (deg)
40
45
50
Summary
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.
MANSE Midterm Review
III. Dilute oxide nanoparticles
LSTO nanoparticle system
Tokura et al, PRL 1988
 spd-band metal.
 0.5 electrons per formula
  = 5 mJ mol-1K-2
 properties depend on oxygen stoichiometry
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.
MANSE Midterm Review
Nanoparticle synthesis
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
MANSE Midterm Review
(La0.5Sr0.5)TiO3:Undoped
18/09/07
300 K
Gel cap I 29.5 mg
Gel cap II 29.3 mg
0.0010
300 K
20 K
10 K
5K
4K
2K
0.0020
0.0006
0.0015
2
Moment (10 Am )
LSTO TCD 65.0 mg Gel cap: 29.0 mg
0.0025
Gel cap I
Gel cap II
0.0008
28/09/07
0.0004
0.0002
2
0.0000
-3
Moment (10 Am )
-3
0.0010
-0.0002
-0.0004
0.0005
0.0000
-0.0005
-0.0010
-0.0006
-0.0015
-0.0008
-0.0020
-0.0010
-5
-4
-3
-2
-1
0
1
2
3
4
5
-0.0025
-4
0H (T)
-2
0
2
0H (T)
Paramagnetism due to S = 1/2 defects in the LSTO particles
MANSE Midterm Review
4
Magnetization
0
2.0
LSTO nanoparticles
LSTO bulk
Gel cap
LSTO nanoparticles + Gel cap
LSTO nanoparticles
LSTO ceramic
-4
1.0
2
Moment (10 Am )
0.5
-8
-6
2
Moment (10 Am )
1.5
0.0
-0.5
-1.0
-1.5
-8
-12
-16
-20
-24
-2.0
-5
-4
-3
-2
-1
0
1
2
3
4
5
0
50
oH (T)
100
150
200
Temperature (K)
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.
MANSE Midterm Review
250
300
TM: LSTO
Co2% LSTO 18.5 mg
4.0
0.3
300 K
200 K
100 K
50 K
4K
Magnetic moment
0.1
3.0
2
-1
Moment (Am kg )
0.2
0.0
Co:LSTO
2% Co
-0.1
Ferromagnetic
Paramagnetic
3.5
-0.2
2.5
2.0
1.5
1.0
0.5
0.0
-0.3
-4
-2
0
2
Sc
4
Ti
V
Cr
Mn
Fe
Co
Ni
Transition metal
0H (T)
100
100
Transmission (%)
Transmission (%)
99
98
96
94
Fe:LSTO
Ceramic
-2
97
96
Fe:LSTO
Nanocrystalline
95
92
-4
Raw
Fit
3+
Fe
2+
Fe
3+
Fe
Fe
98
0
2
4
-10 -8
-1
Velocity (mm s )
MANSE Midterm Review
-6
-4
-2
0
2
4
-1
Velocity (mm s )
6
8
10
LSTO summary
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
MANSE Midterm Review
TM: ZnO nanoparticles
Phys Rev B 2007 Many oxide nanoparticles exhibit a tiny
magnetization < 0.1 A m2 kg-1
 ZnO: 5% M = Sc - Cu
Solvo-/hydrothermal technique
MANSE Midterm Review
Characterization
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.
MANSE Midterm Review
Mössbauer spectra
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
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.
B
MANSE Midterm Review
ZnO nanorods
5%Co-doped ZnO nanorods
Hydrothermal, Zn acetate, Co acetate, NaOH,
120°C for 12h
MANSE Midterm Review
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 (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.
MANSE Midterm Review
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
1.2
10
1.0
5
0.8
Moment (B/Co)
15
-8
2
m (10 Am )
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
-5
0.6
0.4
0.2
-10
-15
-1.0
R-cut
C-cut
0.0
-0.5
0.0
0.5
1.0
0.0
0.2
0.4
0.6
Al content (at.%)
0H (T)
MANSE Midterm Review
0.8
1.0
Band gap widening
100
0.0 % Al
60
0.1% Al
0.2% Al
0.5% Al
0.7% Al
1.0% Al
40
Carrier concentrationn x 10 , cm
Hall Resistance RH, /T
Transmission (%)
80
-3
100
10
20
0
0.001
0.002
0.005
0.01
1
0.1
T = 100 K
0.01
0.0
0.2
0.4
0.6
0.8
1.0
Al nominal concentration, %
1
Eg
20
0.1
0
20
40
0
Eg 
2
2m *
4
5
80
100
(3 2 ne )2/ 3
1
1
1


m * me mh
0.1
ZnCoAlO
 = 0.66(5)
 = 0.33
m* = 0.26(3) me
0.01
0.01
0.0
-6
1
2
3
Energy (eV)
0.1
1
20
(a)
-0.2
-0.4
43.0
-0.6
42.5
Resistance R, k
1
Conductance coeficient 2, x 10 S
0
Eg (eV)
60
Temperature T, K
-0.8
-1.0
41.5
-1.2
41.0
(b)
0
90
180
Angle , deg
270
360
-1.4
0
5
10
-3
nHall x 10 (cm )
42.0
MANSE Midterm Review
10
15
20
25
Temperature T, K
30
35
40
-0.5
Conductance Coefficient 2, S x 10
6
0.0
-1.0
-1.5
-2.0
236ZCAl2 (0.2% Al)
T=2K
T=5K
T = 10 K
T = 20 K
T = 50 K
-2.5
-3.0
-3.5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Magnetic Field 0H, T
1.6
257ZCAl2 (1% Al)
T=2K
T=5K
T = 10 K
T = 20 K
T = 50 K
Conductance Coefficient 2, S
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
2
4
6
8
10
12
14
Magnetic Field 0H, T
MANSE Midterm Review
-8
5.0x10
Data
Exponential Fit
80
Coercive Field Hc, mT
2
Corrected Magnetic Moment mc, Am
100
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
-7
1.0x10
0.0
-8
60
Data: Temp_F
Model: ExpDec1
40
Chi^2/DoF
= 2143.51872
R^2
= 0.98547
-5.0x10
y0
A1
t1
20
3.3
85.7
19.5
±2.6 mT
±3.8 mT
±2.9 K
-7
-1.0x10
-5
-4
-3
-2
-1
0
1
2
3
4
0
5
0
Magnetic Field 0H, T
50
100
150
200
250
300
Temperature T, K
-7
2x10
-7
1.0x10
T = 1.8 K
T = 300 K
-7
-8
9.0x10
Saturating Moment ms, Am
Magnetic Moment m, Am
2
2
1x10
-8
5x10
0
-8
-5x10
-8
8.0x10
-8
7.0x10
-8
6.0x10
-8
5.0x10
Saturating Moment
Linear Fit of Temp_D
-8
2
A = 3.5(3) 10 Am
-7
2
B = 1.2(1) 10 Am K/5T
-8
4.0x10
-7
-1x10
-8
3.0x10
-8
-7
-2x10
-1.00
2.0x10
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
0.0
Magnetic Field 0H, T
0.1
0.2
0.3
0.4
Inverse Temperature 1/T, 1/K
MANSE Midterm Review
0.5
0.6
Summary
Larger moments for films on C-cut substrates compared to
R-cut substrates.
Conductivity is enhanced significantly in films with low
Al doping (0.1-0.2 %), maintaining the magnetic moment.
Magnetic moment decreases with increasing Al content.
Band-gap shift (~ 0.5 eV), is observed with Al-doping.
MANSE Midterm Review
Collaboration
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 within SFI
Symposium on dilute magnetic oxides
MANSE Midterm Review
Future work
Chalcogenides
Detailed characterization on chalcogenide systems (Neutron,
Andreev etc.) and synthesis of single crystals
Delafossite oxides
Make all-oxide heterostructures; pn junctions and pnp stacks.
Nanoparticle systems
Understanding of defects, interface magnetism and detailed
theoretical calculations.
Dilute Oxides
Search for new and novel dilute magnetic oxides by suitable
cation doping.
Heusler alloys
Exploit high Curie temperature Heusler alloys
Co2MnSi, Co2FeSi etc.
Materials developed will continue to be
exploited for applications in MANSE.
MANSE Midterm Review
Outline
 Background
 TiO2:Fe

 Magnetic silicon 
 Graphite

 Anthracene
 MgO:N


 Au nanoparticles 
 A model — Charge-transfer ferromagnetism
MANSE Midterm Review