Epitaxial Alloys of CoMnGe: from Highly Spin Polarized Metals to Magnetic Semiconductors
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Epitaxial Alloys of CoMnGe: from HighlySpin Polarized Metals to Magnetic Semiconductors
Epitaxial Alloys of CoMnGe: from HighlySpin Polarized Metals to Magnetic Semiconductors
Liang He, Lei Ma, and Frank TsuiDepartment of Physics and Astronomy
University of North Carolina at Chapel Hill
Yong. S. ChuAdvanced Photon Source, Argonne National Laboratory
The work is supported in part by NSF DMR-0108605
The work is supported in part by NSF DMR-0108605
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Motivation and ApproachMotivation and ApproachMotivation and Approach
• Motivation:Ternary alloys of CoxMnyGe1-x-y have been predicted to contain many magnetic materials including half-metals that are compatible with semiconductor processing, spintronic and quantum computer applications
• Approach:• Combinatorial synthesis and characterization are
necessary• In-situ measurements: real-time scanning RHEED,
SQUID magnetometry and magnetooptic Kerr effect (MOKE)
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Quartz Crystal
Quartz Crystal
Combinatorial MBE SynthesisCombinatorial MBE Synthesis
Scanning RHEED Gun
Motorized Sample Manipulator/ Heater
Real timeRHEEDImaging
PneumaticShutters
PneumaticShutters
MotorizedMasks
MotorizedMasks
RGA FluxMonitor
RGA FluxMonitor
K-CellE-Gun
AA MonitorsAA Monitors
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MBE Growth and Analysis SystemMBE Growth and Analysis System
SPM
Sources
Features:• 6-axes precision
sample manipulator• Sample temperature
from -100 to 1500 °C
• Up to 8 controlled sources
• In-situ STM, AFM, and SEMM
• Liquid He magnet cryostat for in-situ MOKE and SEMM
Features:• 6-axes precision
sample manipulator• Sample temperature
from -100 to 1500 °C
• Up to 8 controlled sources
• In-situ STM, AFM, and SEMM
• Liquid He magnet cryostat for in-situ MOKE and SEMM
Sample manipulator
LoadlockSample storage
Real-time scanning RHEED imaging
Real-time scanning RHEED imaging
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• 2D – Ternary Sample• 1D – Binary Sample
~ 2Å
Mn
Schematic Diagrams of Combinatorial Sample GrowthSchematic Diagrams of Combinatorial Sample Growth
Ge substrate (111) or (100)
Flux
Mask
Growth Direction
GeCo
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Magnetism and Structure of CoMnGeGrown Epitaxially on Ge (111)
Magnetism and Structure of CoMnGeGrown Epitaxially on Ge (111)
Grown at 350°CAnnealed at 500°C
6
4
2
0
-2
-4
Y (m
m)
-4 -2 0 2 4X (mm)
A B C D E F G H I J
4.2
4.1
4.1
4
4
3.9
3.9
3.8
3
.7
3.6
3.6
Mn
Ge
Co
Room Temperature Saturation MOKE Image X-ray Reciprocal Lattice Map
FCCHCPHCP
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RH
EE
D I
nt
0.0 0.2 0.4 0.6 0.8 1.0
d allo
y/d G
e
0.975
1.000
1.025
(CoxMn1-x)0.75 Ge0.25: Magnetic Metals(CoxMn1-x)0.75 Ge0.25: Magnetic Metals
Composition xComposition x0 1
TC (
K)
0
100
200
300
400
MO
KE
In
tens
ity
0.0 0.2 0.4 0.6 0.8 1.0
M (
emu/
cc)
0
200
400
600
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Co Concentration x
0.0 0.2 0.4 0.6 0.8 1.0
Nom
inal
Thi
ckne
ss (
Å)
0
20
40
60
0.0 0.2 0.4 0.6 0.8 1.0
MOKE Intensity
0.0 0.2 0.4 0.6 0.8 1.0
0
20
40
60
1.000 1.005 1.010 1.015 1.020 1.025
RHEED Intensity d-Spacing
dAlloy/dGe
Structural Evolution of (CoxMn1-x)0.8Ge0.2 Grown on (111) GeStructural Evolution of (CoxMn1-x)0.8Ge0.2 Grown on (111) Ge
Composition x Composition x
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Co0.0 0.2 0.4 0.6 0.8 1.0
Ge
0.0
0.2
0.4
0.6
0.8
1.0
Mn
0.0
0.2
0.4
0.6
0.8
1.0
high
low
Wid
thIn
tens
ity
2D 3D
Composition x
0% 2% 4% 6% 8% 10% 12% 14%
TC
(K)
160
200
240
280 R
HE
ED
Composition dependent Structure and Magnetism of (Co2/3Mn1/3)xGe1-x (x=0-15%)
Composition dependent Structure and Magnetism of (Co2/3Mn1/3)xGe1-x (x=0-15%)
b: 3D
a b
a: 2D
RHEED Patent
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FFTFFT
Cross-sectional TEM of CoMn Doped Ge (100)Cross-sectional TEM of CoMn Doped Ge (100)(C
o 2M
n)0
.05G
e 0.9
5
200Å200Å
100Å
Gefilm Substrate
Dr. Chikyow et al., NIMS, Japan
FFT
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3.97 3.98 3.99 4 4.01 4.021 10 6
1 10 5
1 10 4
1 10 3
0.01
0.1
1
10
100
1 103
127.277
5.409 10 6
In
y n
4.033.97 xn
3.97 3.98 3.99 4 4.01 4.021 10 5
1 10 4
1 10 3
0.01
0.1
1
10
100
1 103
1 104
1 105
1.527 104
6.055 10 5
In
y n
4.033.97 xn
dfilm/dGe=0.99965(5)x = 1%
Film under slightcompressive strain.
xn
x = 4% dfilm/dGe =1.0011
Film under slighttensile strain.
q
log
(Int
)X-ray Bragg Scan of CoMn Doped Ge (100)
Confirming High Crytalline Quality X-ray Bragg Scan of CoMn Doped Ge (100)
Confirming High Crytalline Quality
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Semiconducting Transport PropertiesSemiconducting Transport Properties
Transport & Magnetism please come to talk by Ma et al. on Thursday, Room 16A, session X24.005
T (K)0 50 100 150 200 250 300 350
xx (
cm
)
10-3
10-2
10-1
100
101
102
103
104
1%4%7%10%13%
1/T (K-1)
0.0 0.1 0.2 0.3 0.4
xx (
cm
)10-3
10-2
10-1
100
101
102
103
104
1% 4% 7%10%13%
39.2 meV
1.50 meV
2.15 meV
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SummarySummary
• A range of ferromagnetic alloys of CoxMnyGe1-x-y with TC > 300 K can be grown coherently on Ge by MBE
• Magnetic ordering shows strong correlation with structural ordering
• A new class of magnetic semiconductors with high TC has been discovered, which is compatible with current semiconductor processing technology