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Epitaxial Alloys of CoMnGe: from Highly Spin Polarized Metals to Magnetic Semiconductors

Epitaxial Alloys of CoMnGe: from Highly Spin Polarized Metals to Magnetic Semiconductors. Liang He, Lei Ma, and Frank Tsui Department of Physics and Astronomy University of North Carolina at Chapel Hill Yong. S. Chu Advanced Photon Source, Argonne National Laboratory.

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Epitaxial Alloys of CoMnGe: from Highly Spin Polarized Metals to Magnetic Semiconductors

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  1. Epitaxial Alloys of CoMnGe: from HighlySpin Polarized Metals to Magnetic Semiconductors Liang He, Lei Ma, and Frank Tsui Department of Physics and Astronomy University of North Carolina at Chapel Hill Yong. S. Chu Advanced Photon Source, Argonne National Laboratory The work is supported in part by NSF DMR-0108605

  2. Motivation and Approach Motivation 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)

  3. Combinatorial MBE Synthesis Motorized Sample Manipulator/ Heater Real time RHEED Imaging Scanning RHEED Gun Quartz Crystal Motorized Masks RGA Flux Monitor AA Monitors Pneumatic Shutters K-Cell E-Gun

  4. MBE Growth and Analysis System Sample manipulator • 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 SPM Real-time scanning RHEED imaging Sample storage Loadlock Sources

  5. Schematic Diagrams of Combinatorial Sample Growth ~ 2Å • 2D – Ternary Sample • 1D – Binary Sample Flux Mask Growth Direction Ge substrate (111) or (100) Co Mn Ge

  6. Magnetism and Structure of CoMnGeGrown Epitaxially on Ge (111) Grown at 350°C Annealed at 500°C Ge HCP FCC HCP Co Mn Room Temperature Saturation MOKE Image X-ray Reciprocal Lattice Map

  7. (CoxMn1-x)0.75 Ge0.25: Magnetic Metals Composition x 0 1 Composition x

  8. Structural Evolution of (CoxMn1-x)0.8Ge0.2 Grown on (111) Ge Compositionx Compositionx

  9. Composition dependent Structure and Magnetism of (Co2/3Mn1/3)xGe1-x (x=0-15%) high low a b RHEED Patent a: 2D b: 3D

  10. Cross-sectional TEM of CoMn Doped Ge (100) 200Å (Co2Mn)0.05Ge0.95 100Å FFT FFT film Substrate Ge 200Å Dr. Chikyow et al., NIMS, Japan

  11. X-ray Bragg Scan of CoMn Doped Ge (100) Confirming High Crytalline Quality dfilm/dGe=0.99965(5) x = 1% Film under slight compressive strain. log (Int) dfilm/dGe =1.0011 x=4% Film under slight tensile strain. x n q

  12. Semiconducting Transport Properties Transport & Magnetism please come to talk by Ma et al. on Thursday, Room 16A, session X24.005

  13. Summary • 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

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