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

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)

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

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

• 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

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

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

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

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

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

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

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

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