Spintronics: How spin can act on charge carriers and vice versa Tomas Jungwirth University of Nottingham Institute of Physics Prague

Mott with spin current Dirac with current through magnet Mott without spin current  ‪ Spintronics ‬ From Wikipedia, the free encyclopedia Spintronics (a pormanteau meaning spin transport electronics).... Dirac without current through magnet II II MRAM 2006 GMR 1988 AMR 1857 HD Read-heads 1990‘s

I I I I Mott with ferromagnets Dirac with ferromagnets Dirac with antiferromagnets II II Mott with antiferromagnets 

Magnetic-field control of FMs: scales with current Control by current via spin torques: scales with current density 0.1 pJ Electro-static field control via relativistic magnetic anisotropy effects: 1fJ (or piezo-electric) Should work equally well or better in AFMs: more choices including SCs Control by photo-carriers via spin torques: sub ps timescales Relativistic spin-orbit torques might work equally well in AFMs plus photocarriers in SCs Laser

Writing by current via spin torques: scales with current density 0.1 pJ Writing by photo-carriers via spin torques: sub ps timescales Relativistic spin-orbit torques might work equally well in AFMs plus photocarriers in SCs Laser

Optical spin-transfer torque Fernandez-Rossier, Nunez, Abofath, MacDonald cont-mat/  M  M ss PnPn OSTT M ss M PnPn Němec, Tesařová, Novák, TJ et al. Nature Phys.’12, Nature Photonics ‘13, Nature Commun. ‘13

Fernandez-Rossier, Nunez, Abofath, MacDonald cont-mat/ ss PnPn OSTT M ss M PnPn  Optical spin-transfer torque Němec, Tesařová, Novák, TJ et al. Nature Phys.’12, Nature Photonics ‘13, Nature Commun. ‘13

Fernandez-Rossier, Nunez, Abofath, MacDonald cont-mat/ ss PnPn OSTT M ss M PnPn  Optical spin-transfer torque Němec, Tesařová, Novák, TJ et al. Nature Phys.’12, Nature Photonics ‘13, Nature Commun. ‘13

Zhang and Li PRL 2004 Vanhaverbeke et al. PRB 2007, ss PnPn OSTT M Antidamping-like (adiabatic) STT Electrical spin-transfer torque

ss M PnPn Zhang and Li PRL 2004 Vanhaverbeke et al. PRB 2007, Field-like (non-adiabatic) STT Electrical spin-transfer torque

~ small  in weakly SO-coupled dense-moment metal FMs large  in strongly SO-coupled dilute-moment (Ga,Mn)As Antidamping-like STTField-like STT Electrical spin-transfer torque

Electrical spin-transfer torque: current induced DW motion

Zhang & Li, PRL 93, (2004) Vanhaverbeke & Viret, PRB 75, (2007) v DW j  = 0 jCjC “intrinsic” pinning Electrical spin-transfer torque: current induced DW motion Antidamping STT Antidamping-like STT 

Zhang & Li, PRL 93, (2004) Vanhaverbeke & Viret, PRB 75, (2007) v DW j jCjC  <  Electrical spin-transfer torque: current induced DW motion Antidamping-like STT Field-like STT Antidamping STT 

Zhang & Li, PRL 93, (2004) Vanhaverbeke & Viret, PRB 75, (2007) v DW j  >   <  jCjC jCjC Electrical spin-transfer torque: current induced DW motion Antidamping-like STT Antidamping STT Field-like STT 

Non-relativistic STT External Steady-state carrier spin polarization  torque QM averaging in non-equilibrium Steady state M Electrical spin injection Optical spin injection antidamping-like torque

Relativistic SOT Internal Steady-state carrier spin polarization  torque Steady state M Optical spin injection Electrical spin injection QM averaging in non-equilibrium

Relativistic SOT Internal Steady-state carrier spin polarization  torque Electrical drift and relaxation: broken inversion symmetry Optical generation and relaxation Linear response: eigenstates of H & non-equilibrium distribution Steady state

Paramagnets Magnetic field of moving nucleus in electron‘s rest frame Spin-orbit Electrical drift and relaxation: broken inversion symmetry Spin-galvanic effect = SOT without acting on Aronov, Lyanda-Geller, JETP ’89, Edelstein SSC ’90, Ganichev et al. Nature ‘02

Paramagnets Magnetic field of moving nucleus in electron‘s rest frame Spin-orbit Spin Hall effect

Hall antidamping STT Ralph, Buhrman,et al., Science ‘12 SHE in Pt acts as the external polarizer MRAM switching by in-plane current  SHE  spin-current  non-relativistic STT

MRAM switching by in-plane current  attractive alternative to perp. current STT Conventional perpendicular current STT

MRAM switching by in-plane current  attractive alternative to perp. current STT

Competing scenario: In-plane current swithing by relativitic SOT due to broken structural inversion symmetry at Co/Pt? Miron et al., Nature ‘11

Ralph, Buhrman et al.: SHEMiron et al.: SOT -We see antidamping-like torque -SOT is field-like so we exclude it - non-relativistic STT in metals is dominated by the antidamping torque -We also see antidamping-like torque -SOT is field-like but maybe there is some antidamping-like SOT as well

Where could a comparable strength antidamping-like SOT come from?