spintronic transistors: magnetic anisotropy and direct charge depletion concepts
DESCRIPTION
Spintronic transistors: magnetic anisotropy and direct charge depletion concepts. Tom as Jungwirth. Universit y of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, et al. Institute of Physics ASCR - PowerPoint PPT PresentationTRANSCRIPT
Spintronic transistors: magnetic anisotropy and direct charge depletion concepts
Tomas Jungwirth
University of Nottingham Bryan Gallagher, Tom Foxon,
Richard Campion, Kevin Edmonds, Andrew Rushforth, et al.
Hitachi Cambridge, Univ. Cambridge Jorg Wunderlich, Andrew Irvine, David Williams,
Elisa de Ranieri, Byonguk Park, Sam Owen, et al.
Institute of Physics ASCR Alexander Shick, Karel Výborný, Jan Zemen, Jan Masek, Vít Novák, Kamil Olejník, et al.
University of Texas Allan MaDonald, et al.
Texas A&MJairo Sinova, et al.
Electric field controlled spintronics
HDD, MRAMcontrolled by Magnetic field
Spintronic TransistorLow-V 3-terminal
devices
STT MRAMspin-polarized charge current
1) indirect via magnetic anisotropy
2) direct charge depletion effects
AMRAMR TMRTMR
TAMRTAMR
) vs.( ~ IMvg
M
FM exchange int.:
Spin-orbit int.:
FM exchange int.:
)()( TDOSTDOS
)(MTDOS
Au
Discovered in GaMnAs Gould et al. PRL’04
parallel state
antiparallel state
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
Consider uncommon TM combinationse.g. Mn/W voltage-dependent upto ~100% TAMR
spontaneous momentmag
netic su
sceptib
ility
spin
-orb
it cou
plin
g
Optimizing TAMR in transition-metal structures
Shick, et al PRB ‘08
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
Mn-d-like localmoments
As-p-like holes
Mn
Ga
AsMn
EF
DO
S
Energy
spin
spin
Ferromagnetic semiconductor GaAs:Mn
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
- random dilute moment FM difficult to achieve high Tc
- intrinsically very disordered system
- heavily-doped SC difficult to grow and gate
Exchange-split, SO-coupled, & itinerant holes
FM & transport in the disordered GaMnAs DMS
Ordered magnetic semiconductors
Eu - chalcogenides
Disordered DMSs
Sharp critical contribution to resistivity at Tc ~ magnetic susceptibility
Broad peak near Tc and disappeares with annealing (higher uniformity)
~)( dF
Eu0.95Cd0.05S
][~),(~)( 002 SSSSJTRT iipdi
Fisher&Langer, PRL‘68
singular
UdF ~)~(
vcdTdUdTd /~/
Tc
Ni, Fe
singular
Scattering off correlated spin-fluctuations
Optimized GaMnAs materials with x~4-12% and Tc~80-185K: very well behaved FMs
Annealing sequence
In GaMnAs F~d- sharp singularity at Tc in d/dT
Novak et al., PRL ‚08
Low-voltage gating of the highly doped (Ga,Mn)As
p-n junction depletion simulations
~25-50% depletion feasible at low voltages
2x 1019 cm-3
Owen, et al. arXiv:0807.0906
10’s-100’s Volts in conventional MOS FETs Ohno et al. Nature ’00, APL ‘06
p-n junction FET
Complete spintronic FET characteristics
TcTc
Magnetization switching by short low-Vg pulses
Due to voltage-controlled Kc and Ku anisotropies
semiquantitative microscpic theory understanding
depletion/accumulation & high-frequency studies of DMS materials and spintronics
-1V +3 V
ConclusionConclusion
1) 1) Studies in GaMnAs suggest new generic approaches to Studies in GaMnAs suggest new generic approaches to
electric field controlled spintronics via magnetic anisotropieselectric field controlled spintronics via magnetic anisotropies - TAMR- TAMR - CBAMR - CBAMR
2) 2) Optimized GaMnAs is excellent itinerant FM; low-voltage Optimized GaMnAs is excellent itinerant FM; low-voltage charge depletion effects on electric&magnetic properties charge depletion effects on electric&magnetic properties
demonstrated in all-semiconductor p-n junction transistordemonstrated in all-semiconductor p-n junction transistor - d- d/dT singularity at T/dT singularity at Tcc
- GaMnAs junction FET - GaMnAs junction FET
Tc
(Ga,Mn)As growth
Low-T MBE to avoid precipitation & high enough T to maintain 2D growth need to optimize T & stoichiometry for each Mn-doping
high-T growth optimal-T growth
Annealing also needs to be optimized for each Mn-doping
Detrimental interstitial AF-coupled Mn-donors need to anneal out (Tc can increase by more than 100K)
Tc up to 187 K at 12% Mn doping
0 1 2 3 4 5 6 7 8 9 100
20
40
60
80
100
120
140
160
180
TC(K
)
Mntotal
(%)
No indication for reaching technological or physical Tc limit in (Ga,Mn)As yet
Novak et al. PRL ‘08
1998
2005Growth & post-growth optimized GaMnAs films
Weak hybrid.Delocalized holeslong-range coupl.
Strong hybrid.Impurity-band holesshort-range coupl.
InSb
GaP
d5
GaAs seems close to the optimal III-V host
Other (III,Mn)V’s DMSs
Mean-field butlow Tc
MF
Large TcMF but
low stiffness
Kudrnovsky et al. PRB 07
Magnetism in systems with coupled dilute moments and delocalized band electrons
cou
pli
ng
str
eng
th /
Fer
mi
ener
gy
band-electron density / local-moment density
Jungwirth et al, RMP '06
III = I + II Ga = Li + Zn
Other DMS candidates
Masek et al. PRL 07But Mn isovalent in Li(Zn,Mn)As
no Mn concentration limit and self-compensation
possibly both p-type and n-type ferromagnetic SC
(Li / Zn stoichiometry)
GaAs and LiZnAs are twin SC
(Ga,Mn)As and Li(Zn,Mn)As
should be twin ferromagnetic SC
Sharp d/dT singularity in GaMnAs at Tc – consistent with F~d-
Novak, et al. PRL‘08
As-p-like holes
Strong spin-orbit coupling favorable for spintronics
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
Mn
Ga
AsMn