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Anisotropic magnetoresistance effects in ferromagnetic semiconductor and metal devices

Anisotropic magnetoresistance effects in ferromagnetic semiconductor and metal devices. 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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Anisotropic magnetoresistance effects in ferromagnetic semiconductor and metal devices

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  1. Anisotropic magnetoresistance effects in ferromagnetic semiconductor and metal devices 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, et al. Hitachi Labs., UK & Japan University of Texasand Texas A&M Jorg Wunderlich, Byong-Guk Park, Andrew Irvine,Allan MacDonald, Jairo Sinova David Williams, Akira, Sugawara, et al. University of Wuerzburg Polish Academy of Sciences Tohoku University Laurens Molenkamp, Charles Gould Tomasz Dietl, et al. Hideo Ohno, et al.

  2. Outline • 1. Intro - basic micromagnetics in DMSs • 2. DMS materials science • 3. AMR effects in DMSs and metals – devices and physics

  3. Ga Mn As Mn (Ga,Mn)As: an archetypical dilute moment FM semiconductor 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 Mn-Mn coupling mediated by holes in SO-coupled SC valence bands: sensitive to gating, comparable magnetocrystalline anisotropy energy and stiffness to metal FMs For not too strong p-d hybridization: kinetic-exchange (Jpd) & host SC bands provides simple yet often semiquantitative description

  4. Macro (100’s m) domains; 10-100 nm domain walls (~A/K) reflecting combined T-dependent uniaxial and cubic anisotropies MF-like M(T); square hysteresis loops 1 mm 500 nm 22 K 8 K

  5. One One Strain controlled micromagnetics and current induced DW dynamics  tunable 100x smaller critical currents than in metals 0.1-1 m Huge hysteretic MR tunable by gate due to CBAMR  spintronic transistor … plus weak dipolar crosslinks  prospect for dense integration of magnetic microelements

  6. Outline • 1. Intro - basic micromagnetics in DMSs • 2. DMS materials science • 3. AMR effects in DMSs and metals – devices and physics

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

  8. 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

  9. MIT in GaAs:Mn at order of magnitude higher doping than quoted in text books

  10. MIT in p-type GaAs: - shallow acc. (30meV) ~ 1018 cm-3 - Mn (110meV) ~1020 cm-3 Mobilities: - 3-10x larger in GaAs:C - similar in GaAs:Mg or InAs:Mn > 2% Mn: metallic but strongly disordered   Mn spacing Model: SO-coupled, exch.-split Bloch VB & disorder - conveniently simple and increasingly meaningful as metallicity increases - no better than semi-quantitative

  11. Mnsub MnInt Mnsub - As + MnInt Ga MnGa solubility limit Covalent SCs do not like doping self-compensation by interstitial Mn Interstitial MnInt is detrimental to magnetic order charge and moment compensation defect Can be annealed out Tc 95K in as-grown (9% Mn) to 173 in annealed (6% Mnsub) but MnGa < nominal Mn theory & exp.

  12. Delocalized holes long-range coupl. Weak hybrid. Search for optimal III-V host: optimal combination of hole delocalization, p-d coupling strength, low self-compensation InSb, InAs, GaAs d5 Impurity-band holes short-range coupl. Strong hybrid. GaP, AlAs d 5 d 4 no holes d GaN d4

  13. I-II-Mn-V 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 • Independent carrier doping by Li-Zn • stoichiometry adjustment

  14. Outline • 1. Intro - basic micromagnetics in DMSs • 2. DMS materials science • 3. AMR effects in DMSs and metals – devices and physics

  15. M || <100> M || <111> Anisotropic, SO-coupled, exchange-split hole bands Chemical potential  CBAMR M Tunneling DOS  TAMR M I Impurity scattering rates  AMR I

  16. M [010] [110] F [100]  [110] [010] Coulomb blockade AMR – anisotropic chemical potential Q VD Source Drain Gate VG magnetic electric & control of Coulomb blockade oscillations

  17. Worth trying to look for CBAMR in SO-coupled room-Tc metal FMs • CBAMR if change of |(M)| ~ e2/2C • In our (Ga,Mn)As ~ meV (~ 10 Kelvin) • In room-T ferromagnet change of |(M)|~100K • Room-T conventional SET • (e2/2C>300K) possible

  18. 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

  19. TAMR in metals theory experiment

  20. Anisotropic magnetoresistance Semiquantitative numerical understanding in GaMnAs THEORY EXPERIMENT

  21. Qualitative physical (analytical) picture anisotropic scattering SO & polarized scatterers

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