Institute of Physics ASCR Tomas Jungwirth, A lexander Shick , Karel Výborný, Jan Zemen,

1. Prague IoP group and theoretical studies of ferromagnetic materials and nanostructure with strong spin-orbit coupling Institute of Physics ASCR Tomas Jungwirth, Alexander Shick, Karel Výborný, Jan Zemen, Jan Masek, Jairo Sinova, Vít Novák,Kamil Olejník, et al.

2. 64-node high-performance computer cluster State of the art molecular-bean epitaxy & electron-beam lithography systems

3. Theoretical methods  Electronic structure Analytical models (Rashba, Dresselhaus, spherical-Luttinger) k.p semiphenomenological modelling (typical for semiconductors) extensive library of home-made routines spd-tight-binding modelling (half way between phenomenological and ab initio) home-made relativistic codes Full ab initio heavy numerics (transition metals based structures) standard full-potential libraries, home-made relativistic ab-initio codes  Observables micromagnetic parameters from total energy, thermodunamics, and linear response theories Boltzmann and Kubo equations for extraordinary, anisotropic, and coherent transport  Device specific modeling Finite-element methods, Schrodinger-Poisson solvers, Monte-Carlo semiclassical methods, Landauer-Buttiker formalism

4. As Ga Mn Materials • Semiconductor 2D electron and hole systems with spin-orbit coupled bands  Dilute-moment ferromagnetic semiconductors  Transition metal ferro and antiferromagnets

5. Research goal: Electric field controlled spintronics HDD, MRAM controlled by Magnetic field Spintronic Transistors Low-V 3-terminal devices STT MRAM spin-polarized charge current & Opto-spintronics

6. Paradigms • Exchange & spin-orbit coupling & direct link to spintronics (magnetotransport) • Semiconducting multiferroic systems • Spin dynamics in non-magnetic spin-orbit coupled channels

7. Au AMR TMR Exchange & spin-orbit coupling; complex link to transport TAMR Exchange only; direct link to transport Exchange & spin-orbit coupling; direct link to transport

8. Bias-dependent magnitude and sign of TAMR Shick et al PRB ’06, Parkin et al PRL ‘07, Park et al PRL '08 ab intio theory TAMR is generic to SO-coupled FMs experiment Park et al PRL '08

9. TAMR in TM structures Consider uncommon TM combinations Mn/W  ~100% TAMR Consider both Mn-TM FMs & AFMs Shick, et al, unpublished spontaneous moment magnetic susceptibility spin-orbit coupling exchange-spring rotation of the AFM Scholl et al. PRL ‘04 Proposal for AFM-TAMR: first microelectronic device with active AFM component Shick, et al, unpublished

10. Q VD Source Drain M [010] [110] Gate [100] VG [110] [010] Devices utilizing M-dependent electro-chemical potentials: FM SET SO-coupling  (M) ~ mV in GaMnAs ~ 10mV in FePt magnetic electric & control of CB oscillations Wunderlich et al, PRL '06

11. CB oscillations shifted by changing M(CBAMR) (Ga,Mn)As nano-constriction SET Electric-gate controlled magnitude and sign of magnetoresistance  spintronic transistor & Magnetization controlled transistor characteristic (p or n-type)  programmable logic

12. Magnitude and sensitivity to electric fields of the MR Complexity of the relation between SO & exchange-split bands and transport Complexity of the device design Chemical potential  CBAMR SET Tunneling DOS  TAMR Tunneling device Group velocity & lifetime  AMR Resistor

13. Paradigms • Exchange & spin-orbit coupling & direct link to spintronics (magneotransport) • Semiconducting multiferroic systems • Spin dynamics in non-magnetic spin-orbit coupled channels

14. Semiconducting multiferroic spintronics Control via (non-volatile) charge depletion and/or strain effects Magnetic materials spintronic magneto-sensors, memories Semiconductors Ferroelectrics/piezoelectrics electro-mechanical transducors, large & persistent el. fields transistors, logic, sensitive to doping and electrical gating

15. Ga Mn As Mn Ferromagnetic semiconductors Need true FSs not FM inclusions in SCs GaAs - standard III-V semiconductor Group-II Mn - dilute magnetic moments & holes (Ga,Mn)As - ferromagnetic semiconductor

16. Ga Mn As Mn GaAs:Mn – extrinsic p-type semiconductor EF spin  ~1% Mn << 1% Mn >2% Mn DOS Energy spin  onset of ferromagnetism near MIT As-p-like holes localized on Mn acceptors valence band As-p-like holes As-p-like holes FM due to p-d hybridization (Zener local-itinerant kinetic-exchange) Mn-d-like local moments

17. Ga Mn As Mn p s V Beff Ferromagnetism & strong spin-orbit coupling As-p-like holes Strong SO due to the As p-shell(L=1) character of the top of the valence band Beff Bex + Beff

18. Electric field control of ferromagnetism k.p kinetic exchange model predicst sensitivity to strains ~10-4 Strain & SO  Rushforth et al., ‘08 slow and requires ~100V and hole-density variations of ~1019-1020 cm-3

19. Low-voltage gating (charge depletion) of ferromagnetic semiconductors Switching by short low-voltage pulses Magnetization Owen, et al. arXiv:0807.0906

20. Paradigms • Exchange & spin-orbit coupling & direct link to spintronics (magnetotransport) • Semiconducting multiferroic systems • Spin dynamics in non-magnetic spin-orbit coupled channels

21. Spin dynamics in non-magnetic spin-orbit coupled channels Datta-Das transistor Datta and Das, APL ‘99

22. Spin-injection Hall effect transistor and spin-photovoltaic cell Non-destructive detection of spin-dynamics along the channel Compatible with optical and electrical spin-injection and tunable by electrical gates