institute of physics ascr tomas jungwirth, a lexander shick , karel výborný, jan zemen,
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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.
64-node high-performance computer cluster
State of the art
molecular-bean epitaxy
& electron-beam lithography systems
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
Semiconductor 2D electron and hole systems with spin-orbit coupled bands
Dilute-moment ferromagnetic semiconductors
AsAsGaGa
MnMn
Transition metal ferro and antiferromagnets
Materials
Research goal: Electric field controlled spintronics
HDD, MRAMcontrolled by Magnetic field
Spintronic TransistorsLow-V 3-terminal
devices
STT MRAMspin-polarized charge current
& Opto-spintronics
1. Exchange & spin-orbit coupling & direct link to spintronics (magnetotransport)
2. Semiconducting multiferroic systems
3. Spin dynamics in non-magnetic spin-orbit coupled channels
Paradigms
AMRAMR TMRTMR
TAMRTAMR
Exchange & spin-orbit coupling;complex link to transport
Exchange only; direct link to transport
)(MTDOS
Au
Exchange & spin-orbit coupling; direct link to transport
ab intio theoryTAMR is generic to SO-coupled FMs
experiment
Bias-dependent magnitude and sign of TAMR
Shick et al PRB ’06, Parkin et al PRL ‘07, Park et al PRL '08
Park et al PRL '08
spontaneous momentmag
netic su
sceptib
ility
Consider uncommon TM combinationsMn/W ~100% TAMR
Consider both Mn-TM FMs & AFMs
exchange-spring rotation of the AFMScholl et al. PRL ‘04
Proposal for AFM-TAMR: first microelectronic device with active AFM component
spin
-orb
it cou
plin
g
TAMR in TM structures
Shick, et al,unpublished
Shick, et al,unpublished
GM
MGG
C
C
e
MV
MVVCQC
QQU
)(&
)]([&2
)(0
20
electric && magneticmagnetic
control of CB oscillations
Source Drain
GateVG
VDQ
Devices utilizing M-dependent electro-chemical potentials: FM SET
SO-coupling (M)
[010] M[110]
[100]
[110][010]
~ mV in GaMnAs~ 10mV in FePt
Wunderlich et al, PRL '06
(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
Complexity of the relation between SO & exchange-split bands and
transport
SET
Resistor
Tunneling device
Chemical potential CBAMR
Tunneling DOS TAMR
Group velocity & lifetime AMR
Complexity of the device design
Magnitude and sensitivity to electric
fields of the MR
1. Exchange & spin-orbit coupling & direct link to spintronics (magneotransport)
2. Semiconducting multiferroic systems
3. Spin dynamics in non-magnetic spin-orbit coupled channels
Paradigms
Magnetic materials
Ferroelectrics/piezoelectrics Semiconductors
spintronic magneto-sensors, memories
electro-mechanical transducors, large & persistent el. fields
transistors, logic,sensitive to doping and electrical gating
Semiconducting multiferroic spintronics
Control via (non-volatile) charge depletion and/or strain effects
Ferromagnetic semiconductors
GaAs - GaAs - standard III-V semiconductorstandard III-V semiconductor
Group-II Group-II Mn - Mn - dilute dilute magneticmagnetic moments moments & holes& holes
(Ga,Mn)As - fe(Ga,Mn)As - ferrromagneticromagnetic semiconductorsemiconductor
Need true FSs not FM inclusions in SCs
Mn
Ga
AsMn
Mn-d-like localmoments
As-p-like holes
Mn
Ga
AsMn
EF
DO
S
Energy
spin
spin
GaAs:Mn – extrinsic p-type semiconductor
FM due to p-d hybridization
(Zener local-itinerant kinetic-exchange)
valence band As-p-like holes
As-p-like holes localized on Mn acceptors
<< 1% Mn ~1% Mn >2% Mn
onset of ferromagnetism near MIT
As-p-like holes
Ferromagnetism & strong spin-orbit coupling
LSdr
rdV
err
mc
p
mc
SeBH effSO
)(1
Strong SO due to the As p-shell (L=1) character of the top of the valence band
V
BBeffeff
pss
Beff Bex + Beff
Mn
Ga
AsMn
Rushforth et al., ‘08
Strain & SO
Electric field control of ferromagnetism
k.p kinetic exchange model predicst sensitivity to strains ~10-4
and hole-density variations of ~1019-1020 cm-3
slow and requires ~100V
Low-voltage gating (charge depletion) of ferromagnetic semiconductors
Owen, et al. arXiv:0807.0906
Switching by short low-voltage pulses
Mag
neti
zati
on
1. Exchange & spin-orbit coupling & direct link to spintronics (magnetotransport)
2. Semiconducting multiferroic systems
3. Spin dynamics in non-magnetic spin-orbit coupled channels
Paradigms
Datta-Das transistor
Spin dynamics in non-magnetic spin-orbit coupled channels
Datta and Das, APL ‘99
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
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