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Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals)

Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals). Tom as Jungwirth. Universit y of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, Chris King et al. Institute of Physics ASCR

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Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals)

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  1. Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals) Tomas Jungwirth University of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, Chris King et al. Institute of Physics ASCR Alexander Shick, Jan Mašek, Josef Kudrnovský, František Máca, Karel Výborný, Jan Zemen, Vít Novák,Kamil Olejník, Jairo Sinova et al. Hitachi Labs., UK & Japan Jorg Wunderlich, Byong-Guk Park, Andrew Irvine, Elisa De Ranieri, Samuel Owen, David Williams, Akira, Sugawara, et al.

  2. Outline • 1. Intro – spin-orbit coupling in spintronics • 2. GaMnAs based spintronic devices • 3. GaMnAs and other spin-orbit coupled ferromagnetic materials

  3. & & e- Spintronics … it’s all about spin and charge of electron communicating Spin-orbit couping nucleus rest frame electron rest frame Lorentz transformation  Thomas precession SO-couping = E&M and postulated electron spin 2 2 2

  4. total wf antisymmetric = * spin wf symmetric (aligned) orbital wf antisymmetric e- e- e- Ferromagnetism = Pauli exclusion principle & Coulomb repulsion DOS … collective communication DOS macroscopic moment  large effects

  5. < AMR GMR ~ 1% MR effect ~ 10% MR effect FM only ( ) FM & SO-coupling (M ) + larger MR - low-resistance, non-linear, spin-coherence, exchange biasing or interlayer coupling, higher noise + linear sensing, low-noise - low MR, low-resistance TAMR CBAMR TMR ~ 100% MR effect Au AlOx Au TDOS TDOS TDOS (M ) chem. pot. + very large MR, high resistance, bistable  memory - non-linear, spin-coherence, exchange biasing, higher noise Combining “+” and eliminating “-” of AMR and TMR(GMR) & SET gating  spintronic transistor

  6. SO-coupling  magnetocrystalline anisotropies  sensitivity to lattice distortions Ferromagnetic/magnetostrictive magneto-sensors, transducors, memory, storage piezo/FM hybrids FM semiconductors Semicondicting/gatable Ferroelectric/piezoelectric electro-sensors, transducors, memory transistors, processors FeFET Systems integrating all three basic elements of current microelectronics

  7. Outline • 1. Intro – spin-orbit coupling in spintronics • 2. GaMnAs based spintronic devices • 3. GaMnAs and other spin-orbit coupled ferromagnetic materials

  8. Ga Mn As Mn (Ga,Mn)As: archetypical system for SO-coupling based spintronics research As-p-like holes SW-transf.  JpdSMn. shole Mn-d-like local moments Dilute Mn-doped SC: sensitive to doping; 100smaller Ms than in conventional metal FMs  weak dipolar fields Mn-Mn coupling mediated by holes in SO-coupled SC valence bands: sensitive to gating, comparable magnetocrystalline anisotropy energy and stiffness to metal FMs Model sp-d ferromagnet: kinetic-exchange (Jpd) & host SC bands provides simple yet often semiquantitative description

  9. M || <100> M || <110> M [010] [110] F [100] [110] [010] (M) Coulomb blockade AMR – anisotropic chemical potential Q VD Source Drain Gate VG magnetic electric & control of Coulomb blockade oscillations

  10. AlOx Au GaMnAs M perp. Magnetisation in plane Resistance M in-plane Au Tunneling AMR – anisotropic TDOS TAMR in GaMnAs Anisotropc tunneling amplitudes ~ 1-10% in metallic GaMnAs Huge when approaching MIT in GaMnAs

  11. One One Strain controlled micromagnetics 0.1-1 m DW structure and dynamics directly reflecting e.g. (strain dependent) competition between uniaxial and cubic anisotropies 500 nm strain ~ 10-4 … plus 100-10x smaller currents for DW switching and 100-10x weaker dipolar crosslinks  prospect for dense integration of magnetic microelements switchable by low currents

  12. Sensitivity of AMR to lattice distortions bulk ~100nm - 1m wide bars GaMnAs GaAs

  13. Outline • 1. Intro – spin-orbit coupling in spintronics • 2. GaMnAs based spintronic devices • 3. GaMnAs and other spin-orbit coupled ferromagnetic materials

  14. coupling strength / Fermi energy band-electron density / local-moment density Magnetism in systems with coupled dilute moments and delocalized band electrons (Ga,Mn)As

  15. GaAs VB GaAs:Mn extrinsic semiconductor Mn-acceptor level (IB) GaMnAs disordered VB 2.2x1020 cm-3 VB-IB VB-CB   Short-range ~ M . s potential - additional Mn-hole binding - ferromagnetism - scattering

  16. MIT (and ferromagnetism) at relatively large doping  suppressed gating effect MIT in p-type GaAs: - shallow acc. (30meV) ~ 1018 cm-3 - Mn (110meV) ~1020 cm-3 MIT in GaAs:Mn at order of magnitude higher doping than quoted in text books

  17. Delocalized holes long-range coupl. Weak hybrid. Search for optimal III-V host optimal combination of large SO-cupling, hole delocalization, hole-Mn coupling InSb, InAs d5 GaAs GaP Impurity-band holes short-range coupl. Strong hybrid. SO-coupling strength, band-parabolicity AlAs d 5 d 4 no holes d GaN d4

  18. I(II,Mn)V dilute-moment ferromgantic semiconductors III = I + II  Ga = Li + Zn • GaAs and LiZnAs are twin semiconductors • Prediction that Mn-doped are also twin ferromagnetic semiconductors • No limit for Mn-Zn (II-II) substitution • within the same crystal structure • Independent carrier (holes and electrons) • doping by Li-Zn stoichiometry adjustment

  19. I(II,Mn)V as a link between DMSs and high-Tc half-metalic Heuslers, all comaptible with III-V technology Zinc Blende – (III,Mn)V I(II,Mn)V + interstitial FCC + interstitial + interstitial Half Heusler (NiMnSb) Rock Salt + interstitial + interstitial

  20. High Tc large SO-coupling TM thin films and ordered alloys heavy TM FM TM FM TM heavy TM FM TM heavy TM Key: large induced moment on strongly SO-coupled heavy TM spontaneous moment spin-orbit coupling magnetic susceptibility

  21. B. G. Park, J. Wunderlich, D. A. Williams, S. J. Joo, K. Y. Jung, K. H. Shin, K. Olejnik, A. B. Shick, and T. Jungwirth: Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures, submitted to Phys. Rev. Lett. (2007) Akira Sugawara, H. Kasai, A. Tonomura, P. D. Brown, R. P. Campion, K. W. Edmonds, B. L. Gallagher, J. Zemen, and T. Jungwirth: Domain walls in (Ga,Mn)As diluted magnetic semiconductor, Phys. Rev. Lett. in press (2007) A. W. Rushforth, K. Výborný, C. S. King, K. W. Edmonds, R. P. Campion, C. T. Foxon, J. Wunderlich, A. C. Irvine, P. Vašek, V. Novák, K. Olejník, Jairo Sinova, T. Jungwirth, B. L. Gallagher: Anisotropic magnetoresistance components in (Ga,Mn)As, Phys. Rev. Lett. 99 (2007) 147207 J. Masek, J.Kudrnovsky, F. Maca, B. L. Gallagher, R. P. Campion, D. H. Gregory, and T. Jungwirth: Dilute moment n-type ferromagnetic semiconductor Li(Zn,Mn)As, Phys. Rev. Lett. 98 (2007) 067202 J. Wunderlich, T. Jungwirth, B. Kaestner, A. C. Irvine, K.Y. Wang, N. Stone, U. Rana, A. D. Giddings, A. B. Shick, C. T. Foxon, R. P. Campion, D. A. Williams, B. L Gallagher: Coulomb Blockade Anisotropic Magnetoresistance Effect in a (Ga,Mn)As Single-Electron Transistor, Phys. Rev. Lett. 97 (2006) 077201 T. Jungwirth, Jairo Sinova, J. Mašek, J. Kučera, and A.H. MacDonald: Theory of ferromagnetic (III,Mn)V semiconductors, Rev. Mod. Phys. 78 (2006) 809 C. Rüster, C. Gould, T. Jungwirth, J. Sinova, G.M. Schott, R. Giraud, K. Brunner, G. Schmidt, L.W. Molenkamp: Very Large Tunneling Anisotropic Magnetoresistance of a (Ga,Mn)As/GaAs/(Ga,Mn)As Stack, Phys. Rev. Lett. (2005) 027203

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