Matsue, Japan, August 1, 2011 Diluted Magnetic Semiconductors · taken from Walter A. Harrison...
Transcript of Matsue, Japan, August 1, 2011 Diluted Magnetic Semiconductors · taken from Walter A. Harrison...
Diluted Magnetic Semiconductors- An Introduction -
International Conference and School on Spintronics and Quantum Information Technology (Spintech VI)
School Lecture 2 “Diluted Magnetic Semiconductors”
Matsue, Japan, August 1, 2011
Hideo Ohno1,2
1Center for Spintronics Integrated Systems, Tohoku University, Sendai, Japan
2Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Sendai, Japan
1. What you need to know about nonmagnetic semiconductors• Band structure
2. How you make a semiconductor magnetic• Doping and sp-d exchange
3. The consequences of exchange interaction• Spin-split bands and ferromagnetism
4. Making “use” of ferromagnetism in semiconductors• Electrical control of ferromagnetism• Current induced domain wall motion• Tunneling with magnetism
I am indebted to lecturers of earlier Spintechs, many collaborators, particularly Tomasz Dietl and Fumihiro Matsukura, for a number of materials used here.
1. What you need to know about nonmagnetic semiconductors
• Band structure
Electronic band structureFrom Wikipedia, the free encyclopedia
taken from Walter A. Harrison “Electronic Structure and the Properties of Solids–The Physics of Chemical Bond –, 1980
J. R. Chelikowsky and M. L. Cohen, Phys. Rev. B14, 556 (1976)
Bottom of the conduction band: Ga 4sTop of the valence band: As 4p
εs(Ga)
εs(As)
εp(As)
εp(Ga)
Density of states
up spin states down spin states
conduction band
valence band
EC
EV
2. How you make a semiconductor magnetic
• Doping and sp-d exchange
Making semiconductor magnetic
SiIII-VII-VI…
EuSCuCr2Se4…
diluted magnetic semiconductors
Magnetic ion: Mn
Hund rule: Distributing n electrons over 2(2l+1) degenerate atomic orbitals, the lowest energy state is the state that maximize the total spin angular momentum S
Mn: l=2, n=5 -> S=5/2
http://physics.nist.gov
- intra site correlation energy U = En+1 – En
for n = 5, U ≈≈≈≈ 15 eV
- intra-site exchange interaction: ferromagnetic
Hund’s rule: S the highest possiblefor n = 5, ES=3/2 −−−− ES=5/2 ≈≈≈≈ 2 eV
- transition metal atoms, 3d n4s1, e.g., Mn: ferromagnetic
ES=2 −−−− ES=3 ≈≈≈≈ 1.2 eVJs-d ≈≈≈≈ 0.4 eV
4s
3d
Magnetic ion: Mn
II-VI Diluted Magnetic Semiconducotors
+ =
Density of states with transition metal impurity
d states
majority spin states minority spin states
0
0
sdH xN
E xN
αα
= − ⋅
∆ =
s S
S
0
0
pdH xN
E xN
β
β
= − ⋅
∆ =
s S
S
s-d exchange interaction
(potential exchange)
p-d exchange interaction
(hybridization; kinetic exchange)
0
0 0
: Mn composition
: Density of cation site
, : Exchange energy
x
N
N Nα β
( ) ( ) ( ) ( )01n n n n nH x U xU xJ= − − + − − − ⋅r R r R r R s S
( )
( ) ( ) ( )
( )
0
0;
;
nn
BB
B
xxN
V
xN gg
g
µµ
µ
→
→ − = −
→ − =
∑S S r
M rM r S r
MM M r
Virtual crystal approximation
molecular-field approximation
mean-field approximation
III-V Diluted Magnetic Semiconductors
+ =
(Ga,Mn)As, (In,Mn)As, (Ga,Mn)Sb
h
h
hnot to scale
kinetic, Coulomb, central cell correction, p-d exchange interaction
Mn in GaAs
Mn on Ga site: 113 meV acceptor
• d5+hole (weak coupling) ←• d4
• d5+hole (strong coupling)
22
0 00
expe r
H T V xNr r
βε
= − − − − ⋅
s S N0β = -0.9 eV
from spectroscopy
theory: Bhattacharjee & C. Benoit a la Guillaume, Solid State Commun. 113, 17 (2000) exp: M. Linnarsson et al. Phys. Rev. B 55, 6938 (1997)
3. The consequences of exchange interaction
• Spin -split bands and ferromagnetism
Magnetization of localized spins – no holes
M(T,H) = gµBSxeffNoBS[gµBH/kB(T + TAF)]
antiferromagnetic interactions
xeff < x
TAF > 0
Modified Brillouin function
Y. Shapira et al.
no spontaneous magnetization
Density of states with transition metal impurity
d states
majority spin states minority spin states
0E xN α∆ = S
0E xN β∆ = S
s-d exchange interaction
p-d exchange interaction
J. Gaj, Spintech III
-8000o
Faraday effect
xN0|α<S>|
xN0|β<S>|
xN0|β<S>|/3
Splitting of the bands
EC
EV
k
σ+σ−
+1/2
−1/2
−3/2
+3/2
E
σ−
σ+
∆E=2geffµBHS, S=1/2
•geff~400 > 0
•Follows M not H
Measurements of the band splitting
SPINTECH II Joel Cibertmagnetoreflectance: Aggarwal et al. Phys. Rev. B34, 5894 (1986)
sp-d exchange
(Cd,Mn)Te
(Cd,Mn)Se
(Cd,Mn)S
(Zn,Mn)Te
(Zn,Mn)Se
(Cd,Fe)Se
(Zn,Fe)Se
(Cd,Co)Se
material
0.22
0.26
0.22
0.19
0.26
0.25
0.22
0.28
N0α (eV)
-0.88
-1.24
-1.8
-1.09
-1.32
-1.45
-1.74
-1.87
N0β (eV)
1
2
3
4
ZnO
ZnS
ZnSeCdTe
ZnTeCdSe
CdS
0.5 0.6 0.7 0.80.40.4
|N0β|
(eV
)
a (nm)
circles: photoemissionsquares: optical spectroscopy
3. The consequences of exchange interaction
• Spin -split bands and ferromagnetism
GaAs (or InAs) + Mn
Material Science
- MBE system - 250oC
(Ga,Mn)As (1x2)
Single crystal (Ga,Mn)As
0 5 10 15 20
Inte
nsity
(ar
b. u
nit)
time (sec)
shutter opening(Ga,Mn)AsT
S = 250oC
Molecular beam epitaxy of (Ga,Mn )As
250oC Zinc-blende
HT-GaAs c(4x4)
LT-GaAs (1x1)
(Ga,Mn)As (1x2)
320oC MnAs segregation
170oC Polycrystalline
(Ga,Mn)As spotty
(Ga,Mn)As spotty A. Shen et al., J. Cryst. Growth 175/176, 1069 (1997).
[-110] azimuth
ZB-(Ga,Mn)As can be grown by selecting appropriate growth temperature
Highest Mn composition without segregation is about 10%.
Molecular beam epitaxy of (Ga,Mn )As
Extended X-ray-Absorption Fine Structure (EXAFS)
· X-ray is absorbed by target atom → creation of photoelectron· Photoelectron is scattered by adjacent atoms· Interference of photoelectron and reflected photoelectron· Oscillating structure in absorption spectra includes the information of
local structure around target atom
Incident X-ray Transmitted X-ray
Sample
X-ray
Target atom Adjacent atoms
Absorption edge
Abs
orpt
ion
coef
ficie
nt
Incident X-ray energy
0.0 0.3 0.6
R (nm)
Mn inGaAs (cal.)
MnAs (cal.)
x = 0.005
MnAs
x = 0.074
4As12As
12Ga
12Mn6As
6As
6Mn
2Mn
6As
12Mn6As6As6Mn2Mn
6As
4As 12As12Ga
12Ga 12As4As
FT
(kχ)
(ar
b. u
nits
)
(Ga,Mn)As
Most of Mn substitute III-cation site (Mn2+ → acceptor)
R. Shioda et al., Phys. Rev. B 58, 1100 (1998).
Local Structures - Extended X-ray-Absorption Fine Structure (EXAFS)
Atom Probe Microscopy of (Ga,Mn )As
Surface direction
~ 4
5 nm
~ 90 nm
~ 42 nm~ 1
0 nm
Ga
Mn
As
Analysis direction
M. Kodzuka, T. Ohkubo, K. Hono (NIMS) F. Matsukura, and H. Ohno (Tohoku), Ultramicroscopy 2009
(Ga,Mn)As
Magnetism, transport, and more materials science
Magnetization of (Ga,Mn )As
(Ga,Mn)As & (In,Mn)As: Mn acts as a source of spin and hole
D. Chiba et al., APL 90, 122503 (2007)
Ferromagnetism in (In,Mn)As: H. Ohno et al., Phys Rev. Lett. 1992and in (Ga,Mn)As: H. Ohno et al., Appl. Phys. Lett. 1996
xeff = 0.09, t = 5 nm
-0.5 0.0 0.5-0.04
0.00
0.04
0 50 1000.00
0.03
x = 0.035T = 5 K
B // plane B ⊥ plane B ⊥ plane
(from transport)
M (
T)
B (T)
-0.02 0.00 0.02-0.03
0.00
0.03
M
r (T
)
T (K)
RHall = (R0/d)B + (RS/d)M⊥
H. Ohno et al. Appl. Phys. Lett. 1996H. Ohno Science 1998
RHall = VHall/IRsheet ∝ Vsheet/I
Magnetization and transport of (Ga,Mn )As
Hall Effects
Ordinary Hall effect Anomalous Hall effect Spin Hall effect
0
10
20
30
(a)
RH
all (
Ω)
22 24 26 2829.5
30.0
30.5
experimental linear fit
B (T)
RH
all (
Ω)
0 5 10 15 20 25 30-0.20
-0.16
-0.12
-0.08
-0.04
0.00
B (T)
(b)
1.8K
10K 50mK
100K
∆ρ/ρ
0
xMn=0.053
p = 3.5 x 1020 cm-3
(30% of Mn)
Hall 0
0
( )
1
SR B R M
R B
Bqpd
ρ ⊥∆ = ∆ +≈ ∆
= ∆
Low -temperature & high -field measurements
T. Omiya et al. Physica E, 2000
Ga0.947Mn0.053As
21 3[ ] 1.2 10 cmMn −= ×
10 100
10-2
10-1
100
Ta = 260oC
Ta = 220oC
Ta = 310oC
as-grown
annealed for 15 min(Ga,Mn)As x = 0.05
TS = 210oC
As4/Ga ~ 3
ρ (Ω
cm)
T (K)
0.5670
0.5672
0.5674
0.5676
220 240 260 280 300 320
70
80
90
100
5
6
7
a (n
m)
Ta (oC)
TC (
K)
(x1019)
p (cm-3)
T. Hayashi et al., Appl. Phys. Lett. 78, 1691 (2001).
See also K. W. Edmonds et al., Appl. Phys. Lett. 81, 4991 (2002).
Low -temperature annealing
Low-temperature annealing 220-250 oC· Decreases lattice constant
· Increases electrical conductivity· Increases hole concentration
· Increases ferromagnetic transition temperature
Correlation between TC and p
Mn i
Ferromagnetism
Like other thermodynamic quantities, Fc[M] is expected to be weakly perturbed by static disorder
We suggest that the holes in the extended or weakly localized states mediate the long-range interactions between the localized spins on both sides of the MIT in the III-V and II-VI magnetic semiconductors.
Mn spinsCarrier spins0≠M
β
exchange
p-d Zener model of ferromagnetism
( ) ( )B
FFc k
EASSxNT
12
1 20 βρ+=
T. Dietl, et al. Science 287, 1019 (2000) and PRB 63, 195205 (2001)
Ferromagnetic (Ga,Mn)AsMn acts as a source of spin and hole
also Koenig et al. Phys. Rev. Lett. 2000
s><−= SxNH pd β0
H. Ohno et al. Appl. Phys. Lett. 1996H. Ohno Science 1998
22
2 2
total Mn c
c
Mn
F F F
MH
χχ
∆ = ∆ + ∆
= −
( )Tk
SSxNg
B
BMn 3
1022 += µχ ( )2
c B FEχ µ ρ=
TC by the p-d Zener model
Mn spinsCarrier spins0≠M
β
exchange
( )
22
22
2 22 20
2 2
( )1
812
3
ctotal
Mn
F
BB
B
MF H
EM
gg xN S S
k T
χχ
ρ βµµ
∆ == −
= − +
2
2
2
B
B
EH
M
g
µβ
µ
∆=
=
0
0
∆ 2
∆
B
B
B
E H
E xN S
M xN g S
ME
g
µ
β
µ
βµ
=
=
=
∆ =
22
2 2
( )( )
8F F
cB
A EF M M
g
ρ βµ
∆ ≈ −
( ) ( ) 20 1
12F
cB
xN S S ET
k
ρ β+=
TC by the p-d Zener model
Basis functionsΨΨ EHkp =
k·p matrix
γ1 = 6.85, γ2 = 2.1, γ3 = 2.58, ∆ = 0.34 eV for GaAs
21kP γ= ( )222
2 2 zyx kkkQ −+= γ ( ) zyx kikkL −−= 332 γ ( )[ ]yxyx kkikkM 322
2 23 γγ −−−=, , ,
Valence band structure ( ΓΓΓΓ7, ΓΓΓΓ8)
T. Dietl, H. Ohno and F. Matsukura, Phys. Rev. B63, 195205 (2001)
Valence band structure with p-d exchange ( ΓΓΓΓ7, ΓΓΓΓ8)
ΨΨ EHH pdkp =+ )(
zSxNB β061−= ββ xx b= ββ zz b=
SSw zz = ( ) SSiSw yx ±=±
21222
zyx SSSS ++=
,
,
,
p-d exchange interaction matrix
T. Dietl, H. Ohno and F. Matsukura, Phys. Rev. B63, 195205 (2001)
Exchange energy: N0ββββ
Core level photoemission and modeling:N0β = -1.2 ± 0.2 eV
Okabayashi et al., Phys. Rev. B58, 1998.
Comparison of exp. and calculated TC
0 1 2 3 4 50
50
100
150
, exp. , cal.
(In,Mn)As, x = 0.03
(Ga,Mn)As, x = 0.053
(x1020)
T
C (
K)
Hole concentration, p (cm-3)
Fermi surface of (Ga,Mn)As
Strain induced -anisotropy: Theory vs. Experiment
0
50
100
150
M // [100] : in-plane M // [110] : in-plane M // [001] : ⊥ plane
x=0.05N
0β=-1.2 eV
AF=1.2
compressive strain 0.3 %
TC (
K)
0 1 2 3 4 5
0
50
100
tensile strain 0.7 %
(x1020)
p (cm-3)
-0.10
-0.05
0.00
0.05
0.10
0.15
1.5-µm (Ga0.965Mn0.035)As/LT-GaAs
200-nm (Ga0.957Mn0.043)As/(In0.16Ga0.84)As
^
0o
15o
30o
60o
RH
all (
KΩ
)
-0.5 0.0 0.5-0.03
-0.02
-0.01
0.00
0.01
0.02
0.03
T=2.3 K
B (T)
T=10 K
tensile strain
compressive strain
easy
axis
Bθ
easy
axis
Bθ
Theory Experiment
Hole bands are responsible for the anisotropy
Acceptor doping and susceptibility of Zn 1-xMnxTe:P
0 5 10 15
0
1
2
3
4
5
p ≈ 5×1018 cm-3
p ≈ 1017 cm-3
px = 0.023
p -Zn
1-xMn
xTe
χ-1 [
a.u
. ]
Temperature [ K ]
TCW
Sawicki et al. (Warsaw) pss’02Kępa et al. (Warsaw, Oregon) PRL’03
χ-1 vs. T
1019 10201
10
100
TC (
K)
p (cm-3)
exp, cal, (Ga,Mn)As, x = 0.053
, (In,Mn)As, x = 0.03
, (Zn,Mn)Te, xeff
= 0.015
Comparison of Experimental and Calculated TC
exp.:(Ga,Mn)As:T. Omiya et al., Physica E 7, 976 (2000). (In,Mn)As: D. Chiba et al., J. Supercond. and Novel Mag.16, 179 (2003). (Zn,Mn)Te: D. Ferrand et al., Phys. Rev. B 63, 085201 (2001).
N0β comparison
p-d exchange energy
4. Making “use” of ferromagnetism in semiconductors
• Electrical control of ferromagnetism• Current induced domain wall motion• Tunneling with magnetism
4. Making “use” of ferromagnetism in semiconductors
• Electrical control of ferromagnetism• Current induced domain wall motion• Tunneling with magnetism
Electric-field control of ferromagnetism
-1.0 -0.5 0 0.5 1.0
-50
-25
0
25
50
22.5 K
0 V +1.5 MV/cm -1.5 MV/cm 0 V
R H
all (
Ω)
B (mT)
H. Ohno et al., Nature 408, 944 (2000).
(In,Mn)AsInAs(Al0.6Ga0.4)Sb
AlSbGaAs sub.
5 nm
10 nm400 nm100 nm
(In0.97Mn0.03)Aspolyimide
Au/Cr
800 nm
95/5 nm RHall = (R0/d)B + (RS/d)M⊥
(In,Mn)As
52 56 60 64 68 720.0
0.2
0.4
0.6
0.8
0 1 2 30
50
100
T (K)
RS
Hal
l (kΩ
)
0 MV/cm +5 MV/cm -5 MV/cm
(x1020)
TC
(K
)
p (cm-3)
Electric-field control: the case of (Ga,Mn )As
(Al0.80Ga0.20)As
(In0.13Ga0.87)As
GaAs
(001) GaAs sub.
7 nm
30 nm500 nm100 nm
(Ga0.953Mn0.047)As
Al2O3
Au/Cr
50 nm
100/5 nm
D. Chiba et al. Appl. Phys. Lett. 2006
(In,Mn)As, H. Ohno et al., Nature 408, 944 (2000).
See also Y. Nishitani et al., Phys. Rev. B 81, 045208 (2010) and M. Sawicki, et al., Nature Physics, 6, 22 (2010)
Field -effect structures of (Ga,Mn )As
K. Olejník et al., Phys. Rev. B 78, 054403 (2008); M. S. H. Owen et al., New J. Phys. 11, 023008 (2009).
backgate structure ferroelectric-gate structure
I. Stokichnov et al., Nature Mater. 7, 464 (2008).
M. Overby et al., Appl. Phys. Lett 92, 192501 (2008); A. W. Rushforth et al., Phys. Rev. B 78, 085314 (2008); S. T. B. Goennenwein et al., phys. stat. sol. (RRL) 2, 96 (2008); C. Bihler et al., Phys. Rev. B 78, 045203 (2008).
(Ga,Mn)As
PZT
piezoelectric hybrid structure
electric double layer
M. Endo et al., Appl. Phys. Lett.96, 022515 (2010).
Electric-field control of magnetization direction
-4 -2 0 2 4-10
-5
0
5
10
Gate electric Field E (MV/cm)
H = 0
M A
ngle
ϕ (
deg.
)
[100] axis
2K
Ga0.9Mn0.1As
D. Chiba et al. Nature (2008).
FePt, FePd: M. Weisheit et al., Science (2007).
Multiferroics :::: T. Arima et al., PASPS13 (2009/1/27).
Au/ ultrathin Fe: T. Maruyama et al., Nature Nanotechnology (2009). CoFeB: M. Endo, S. Kanai, S. Ikeda, F.
Matsukura, and H, Ohno, Appl. Phys. Lett. 2010
Electric-field effects on metals
All at room temperatureO-23 Kanai et al.
4. Making “use” of ferromagnetism in semiconductors
• Electrical control of ferromagnetism• Current induced domain wall motion• Tunneling with magnetism
Welp et al., PRL 2003
5 µm
compressive strain in-plane easy axis
90o domains
1 mm
tensile strainperpendicular easy axis
stripe domains
Shono et al., APL 2000
Well defined domains: (Ga,Mn)As
S. I. GaAs (001) sub.GaAs 100 nm
buffer layer
channel layer
In0.22Al0.78As 75 nmGa0.955Mn0.045As 30 nm
easy axis
In0.18Al0.82As 75 nmIn0.13Al0.87As 75 nm
In0.065Al0.935As 75 nm
Current induced domain wall motion
Sample structure
Preparation of domain wall
Patterning of coercive force Hc by etching of (Ga,Mn)As Hc
’ Hc
etching
≠≠≠≠
20 nm 30 nm
Tc ~ 112 K Tc ~ 115 K
Au/Cr electrode 60 µm 20 µm
5 µm
[-110]
[110] (I) (II)
perpendicular easy axis
0 2 4 6 8 10 120
5
10
15
20 107 K 107 K 106 K 105 K 104 K 103 K 102 K 101 K 100 K
v eff (
m/s
)
j (A/cm2)
100 K
x105
M. Yamanouchi et al., Phys. Rev. Lett. 96, 096601 (2006)
Current induced domain wall motion
jcurrent
electron
Mn
Adiabatic spin transfer (conservation of angular momentum)
Mechanism
EF
d state
• Square root dependenceG. Tatara and H. Kohno, Phys. Rev. Lett. 92, 086601 (2004).
2/122 )( CjjAv −=
Domain wall motion: Theory
P
Kej wC
ℏπδ2=
Me
gPA B
2
µ=P : spin polarizationg : g factor of Mn spinµB : Bohr magnetone : charge of electronM : magnetizationK : transverse anisotropyδw : DW width
(Spin transfer)
Current induced domain wall motion
0 2 4 6 8 10 12
0
5
10
15
20 107 K 107 K 106 K 105 K 104 K 103 K 102 K 101 K 100 K
veff (
m/s)
j (A/cm2)
100 K
x105
P
Kej wC
ℏπδ2=
Me
gPA B
2
µ=
102 103 104 105 106 1070.0
0.5
1.0
1.5
2.0
2.5
exp. (square root)
exp. (linear)
A (
m3 /C
)
temperature (K)
x10-9
102 103 104 105 106 1070
2
4
6
8
exp. (linear)
exp. (square root)
j C (
A/c
m2 )
temperature (K)
x105
102 103 104 105 106 1070.0
0.5
1.0
1.5
2.0
2.5
theory
exp. (square root)
exp. (linear)
A (
m3 /C
)
temperature (K)
x10-9
102 103 104 105 106 1070
2
4
6
8
theory
j C (
A/c
m2 )
temperature (K)
Transfer factor and threshold current density
M. Yamanouchi et al., Phys. Rev. Lett. 96, 096601 (2006)
P
Kej wC
ℏπδ2=
(Ga,Mn)As(T/Tc ~ 0.9)
Metal(in plane)
Metal (perpendicular)
K (hard axisanisotropy, J/m3)
60 4x105 105
δw (domain wall width, nm)
20 100 10
P (spin polarization, %)
20 60 60
jC (A/m2) 6x109 7x1013 2 x1012
4. Making “use” of ferromagnetism in semiconductors
• Electrical control of ferromagnetism• Current induced domain wall motion• Tunneling with magnetism
Sample A-1
-0.4 -0.2 0.0 0.2 0.40
100
200
300
2
3
4
5
MR
(%
)
0.39 K+0.5 mV
R(k
ΩΩ ΩΩ)
B [100] (T)
-50 -25 0 25 500
100
200
300
B[100](mT)M
R (
%)
290 %, P = 77 %
Tunnel Magnetoresistance (TMR)
D. Chiba et al. Physica E 2004
20 nm (Ga0.926Mn0.074)As 230-240
6 nm GaAs 250
20 nm (Ga0.956Mn0.044)As 250
50 nm GaAs:Be 560
p+- GaAs (001) sub
2
2
1
2
P
PTMR
−=
Resonant Tunneling Diode with a Ferromagnetic Emitt er
H. Ohno et al. Appl. Phys. Lett., 1998
Resonant Tunnel Diode with a Ferromagnetic Emitter
Sample structures(Ga0.965Mn0.035)As 200 nm
GaAs 15 nmAlAs 5 nmGaAs dW nmAlAs 5 nmGaAs 5 nm
GaAs:Be (5x1017cm-3) 150 nmGaAs:Be (5x1018cm-3) 150 nm
p+ GaAs sub.
Ultra-high doping of Mn in III-V compounds
T. Jungwirth et al., Phys. Rev. B76, 125206 (2007)
Spintech VI, O-10
(Formation of 2D holes in GaAs:Be explains the resonant tunnel-like feature and the thickness dependence)
arXiv 1102.3267v2 (Spintech VI poster FP-42)
Diluted Magnetic Semiconductors
1. What you need to know about nonmagnetic semiconductors• Band structure
2. How you make a semiconductor magnetic• Doping and sp-d exchange
3. The consequences of exchange interaction• Spin-split bands and ferromagnetism
4. Making “use” of ferromagnetism in semiconductors• Electrical control of ferromagnetism• Current induced domain wall motion• Tunneling with magnetism