1. Institute of Physics ASCR
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. Materials As Ga Mn Semiconductor 2D electron and hole systems
with spin-orbit coupled bands As Ga Mn
 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
I think you can remove the history of spintronics devices. You have also too much symbol in your up graph
& Opto-spintronics 5

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

7. AMR TMR TAMR Exchange & spin-orbit coupling; complex link to transportAu
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
Park et al PRL '08
experiment 8

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unpublished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

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

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

16. EF DOS Energy Ga As-p-like holes As Mn Mn-d-like local moments
GaAs:Mn – extrinsic p-type semiconductor
spin  EF
<< 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 Mn Ga As
As-p-like holes
FM due to p-d hybridization
(Zener local-itinerant kinetic-exchange)
Mn-d-like local
moments

17. Mn Ga As As-p-like holes Beff s Beff Bex + Beff
Ferromagnetism & strong spin-orbit coupling Mn Ga As
As-p-like holes V
Beff p s
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 ~ cm-3

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

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