efficient spin injection and absorption using cofe-based alloysfirst demonstration of thermal spin...
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![Page 1: Efficient Spin Injection and Absorption Using CoFe-Based AlloysFirst demonstration of thermal spin injection using NiFe SS np! Seebeck coefficient in FM Generated pure spin current](https://reader036.vdocument.in/reader036/viewer/2022081623/61499d6e12c9616cbc68e03e/html5/thumbnails/1.jpg)
Efficient Spin Injection and Absorption Using CoFe-Based Alloys
Takashi KIMURA
Department of Physics Kyushu University
Fukuoka, Japan
KMS meeting
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Main Contributors & Outline
1.Concept of Spin Current
2.Efficient electrical spin injection
3.Efficient thermal spin injection
4.Spin current absorptions in hybrid systems
Kazuto Yamanoi
SSP Lab D2SSP Lab D2
Tatsuya Nomura
ShaojieHu
Lab PD
Main Contributors
Outline
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Spin current : Flow of spin-angular momentum
Manipulation of magnetization
Charge & Spin
Flow of Charge Electric Current
Flow of Spin Spin Current
Two important innovations for development of spintronics
Concept of spin currents
Manipulation of electric current Spin
current
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j j j
0Sj j j
Charge current (Flow of charge)
Spin current (Flow of spin angular momentum)
j j j
0Sj j j
Conduction electrons in NM & FM
Charge current (Flow of charge)
Spin current (Flow of spin angular momentum)
Ferromagnetic (F) metal
Nonmagnetic (N) metal
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Electrical spin injection
Spin current appears over the spin diffusion length.
x
F NIe
Applying electric field across a F/N junction
x
Spin diffusion length (l)
exp /x l Non-equilibrium spin accumulation
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Highly polarized
Conventional
Spin reabsorption effect in F/N interface
x
Is
Electrical spin injection
CPI
P
0S CI PI
Original spin current is proportional to spin polarization.
Spin polarization cannot
maintain the original value.
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Highly polarized
Conventional
Spin reabsorption effect in F/N interface
x
Is
Backflow can be suppressed
by high spin polarization.
2 N N
F F
1 1I
P
P
l
l
Electrical spin injection
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0 0.2 0.4 0.6 0.8 110-3
10-2
10-1
100
P
21 1I
P
P
Spin reabsorption effect in F/N interface
I
10
Drastic increasedue to spin polarization
Highly polarized
Conventional
x
Is
Spin polarization is key.
N N
F F
l
l
โข Increase of original flowโข Suppression of backflow
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็ดในใใณๆตใฎๆคๅบๆณ๏ผ้ๅฑๆในใใณใใซใๆธฌๅฎๆณEvaluation of spin injection efficiency
Nonlocal spin valve P
AP
S SR I
RS : Spin signalNiFe : P~0.3, CoFeAl : P~ 0.6
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-100 0 100
-5
0
5
Cu
e
HPy
e
CFA
500 nm
H
Py/Cu LSV
CFA/Cu LSV
500 nm
Evaluation of electrical spin injection efficiency
H (mT)
CFA/Cu
Py/Cu
5mฮฉฮR
(mW
)4.8mW
0.33mฮฉ
V
V
Py
CFA
Junction size 130 ร 130nm
S. Hu et al. NPG asia mater. (2014)
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Comparison between Py/Cu and CFA/Cu LSV
Over 10 fold
Distance dependence
R
S(m
W)
V
FM FlF PF
Py0.5
fWm2 0.35 0.015
CFA1.2
fWm2 0.67 0.10
S. Hu et al. NPG asia mater. (2014)
Transparent interface
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Outline
1.Concept of Spin Current
2.Efficient electrical spin injection
3.Efficient thermal spin injection
4.Spin current absorptions in hybrid systems
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ในใใณๆตใฎ็ๆ
Charge current ๐ผC = (๐โ + ๐โ)๐ป๐
Spin current ๐ผS = (๐โ โ ๐โ)๐ป๐
Spin current ๐ผS = (๐โ๐โ โ ๐โ๐โ)๐ป๐
Charge current ๐ผC = (๐โ๐โ + ๐โ๐โ)๐ป๐
Electrical Spin Injection๐โ , ๐โ: Electrical conductivity
Spin current generation due to ๐โ โ ๐โ
๐โ , ๐โ: Seebeck Coefficient
Electrical and Thermal Spin Injection
Thermal spin injection
Spin current generation due to ๐บโ โ ๐บโ
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ในใใณๆตใฎ็ๆ
Charge current ๐ผC = (๐โ + ๐โ)๐ป๐
Spin current ๐ผS = (๐โ โ ๐โ)๐ป๐
Spin current ๐ผS = (๐โ๐โ โ ๐โ๐โ)๐ป๐
Charge current ๐ผC = (๐โ๐โ + ๐โ๐โ)๐ป๐
Electrical Spin Injection๐โ , ๐โ: Electrical conductivity
Spin current generation due to ๐โ โ ๐โ
๐โ , ๐โ: Seebeck Coefficient
Electrical and Thermal Spin Injection
Thermal spin injection
Spin current generation due to ๐บโ โ ๐บโ
S
C
IP
I
02 2
ST S
C
S SI P PP P
I S
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ในใใณๆตใฎ็ๆThermal Spin Injection
Spin current can be injected even at an open circuit condition !!
exp /x l Spin current diminishes with the diffusion.
Spin current ๐ผS = (๐โ๐โ โ ๐โ๐โ)๐ป๐
Charge current ๐ผC = (๐โ๐โ + ๐โ๐โ)๐ป๐
๐โ , ๐โ: Seebeck Coefficient
Thermal spin injection
Spin current generation due to ๐บโ โ ๐บโ
Simplification of device structure
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First demonstration of thermal
spin injection using NiFe
S S
Seebeck coefficient in FM
Generated pure spin current
can be injected into NM
A. Slachter,et al, Nature Physics 6, 879 (2010).
~20 nV
@ RT
Generated spin current is very small because of the small difference in
the Seebeck coefficients for NiFe.
NiFe/Cu lateral spin valve
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Thermally driven spin current in conventional FM
๐ทโ(๐ธ) ๐ทโ(๐ธ)
๐ธ
๐ทโ(๐ธ) ๐ทโ(๐ธ)
๐ธHigh T Low T
FM
F
,
,
E
dD ES
dE
Small spin splitting yields a tiny difference between Sโ and Sโ .
Inefficient situation for
generating spin current
Conventional FM such as NiFe, Ni, etc..
,SS S S S
Small spin-dependent Seebeck coefficient
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Thermally driven spin current in a favorable FM
๐ทโ(๐ธ) ๐ทโ(๐ธ)
๐ธ
๐ทโ(๐ธ) ๐ทโ(๐ธ)
๐ธHigh T Low T
FM
FM with a large exchange splitting
Signs for Sโ and Sโ may be different each other
Highly efficient situation
for generating spin current
0, 0S S
1S
S SP
S S
CoFe-based alloy
F
,
,
E
dD ES
dE
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1ยตm HCu
CoFeAl/Cu lateral spin valve for thermal spin injection
CoFeAl
43โwt% Co
54โwt% Fe
03โwt% Al
Cu
CFA1 CFA2
Temperature distribution under thermal spin injection(COMSOL simulation)
2nd harmonic detection
Joule heating
I
V
2T I
T (K)
โT=64โKโฮผmโ1
at I=0.78โmA
๐ = ๐ 1๐ผ๐ด๐ถ๐ ๐๐๐๐ก+๐ 2๐ผ๐ด๐ถ
2๐ ๐๐2๐๐ก +โฏ
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-100 0 100-62
-61
H(mT)
โ๐๐ 2๐
= 0.873ยตV
-100 0 100-64.4
-64.3
-64.2
-64.1
H(mT)
Evaluation for thermal spin injection property
๐โโ2๐
โ ๐โโ2๐
Anomalous Nernst effect S. Hu and T. Kimura,
Phys. Rev. B 87, 014424 (2013).
CoFeAl/Cu LSV NiFe/Cu LSV
NiFe detector
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0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
Spin voltage
0 0.2 0.4 0.6 0.8 1
-80
-60
-40
-20
0
๐ผ(๐๐ด)
Electric voltage
Confirmation of thermally excited spin current
Both of ๐๐ 2๐
and ๐02๐
are well
reproduced by the parabolic curves.
Clear evidence of thermal spin injection
Bias current dependence
๐02๐
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0 500 1000 1500
0
1
2
L (nm)
๐๐น โ 2๐๐,๐ป๐๐น โ 64๐พ/๐๐(@ ๐ผ = 0.78๐๐ด)ฮป๐ถ๐ข = 500 ๐๐
RT
๐๐ โ โ72.1๐๐/๐พ,
๐โ = โ35.7๐๐/๐พ, ๐โ = 36.4๐๐/๐พ
๐0 =๐โ๐โ+๐โ๐โ
๐โ+๐โ
= โ22๐๐/๐พ
ฮ๐๐ =๐๐น๐ ๐น๐ ๐ถ๐ข๐๐น๐ป๐๐น๐๐
2๐ ๐น ๐ ๐น + ๐ ๐ถ๐ข (cosh ๐ฟ/๐๐ถ๐ข + sinh ๐ฟ/๐๐ถ๐ข ) + ๐ ๐2 sinh(๐ฟ/๐๐ถ๐ข)
๐ =๐โโ๐โ
๐โ+๐โ= 0.62
CuF F
L
Confirmation of thermally excited spin current
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Comparison of thermal spin injection efficiency
CoFeAl/CuSlachter et al.
Nature Physics (2010)NiFe/Cu S. Hu et al.
NPG asia mater. (2014)
22 nV
๐๐ = โ3.8 ๐๐/๐พ ๐๐ = โ72.1 ๐๐/๐พ๐๐ =๐๐๐๐ถ
= 0.19 ๐๐ =๐๐๐๐ถ
= 3.27
@ RT
Spin current density7.46ร108 A/m2
Spin current density3.56ร107 A/m2
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Outline
1.Concept of Spin Current
2.Efficient electrical spin injection
3.Efficient thermal spin injection
4.Spin current absorptions in hybrid systems
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Phys. Rev. B 72, 014461 (2005)
โขWith spin current absorber
Spin current is preferably absorbed
into spin absorber because of
the strong spin relaxation.
โขWithout additional contact
Spin current absorption
Symmetric flow with respect to
the injecting junction
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600 nm
550 nm
Without middle wire
With middle wire
Py Py
Cu
Cu
PyPyPy
T. Kimura et al. Appl. Phys. Lett. 85, 3795 (2004)
Spin current absorption
0.2 mW
0.05 mW
Magnetic field (Oe)
Magnetic field (Oe)
-800 -400 0 400 800-0.4
-0.2
0
0.2
-600 -300 0 300 600-0.4
-0.2
0
0.2
V
/I(m
W)
V
/I(m
W)
R
R=
R=
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Spin current absorption into Superconductor
K. Ohnishi et al. Sci. Rep. (2014)
Nanopillar-based Lateral Spin Valve
Influence of Joule heating is perfectly removed.
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Spin transport in Cu/Nb bilayer
H (mT)
Spin signal at 10 K is strongly
reduced by spin absorption into Nb.
After the transition, it seems no spin absorption.
0. 8 mW
~0. 8 mW
~0. 2 mW
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Longitudinal spin current Transverse spin current
A 2
21
1
LRSP
l
A
2 TRS
l
Relaxation lengths for longitudinal spin
Spin penetration depthSpin diffusion length
Longitudinal and transverse spin current absorptions
The absorption efficiency depends on the relative angle between the injecting
spin and the localized magnetic moment.
02 5 nmL sfD 02 / 1 nmT D J
Relaxation lengths for transverse spin
S. Nonoguchi et al. PRB (2012)
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Longitudinal configuration
Transverse configuration
Spin current is moderately absorbed into the FM3.
Spin current is strongly absorbed into the FM3.
By controlling these two states, the spin signal can be modulated.
Spin absorption into a FM/NM bilayer
Modulation efficiency depends on
& PFM3๐ ๐ฟ / ๐ ๐
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Nonlocal spin signal with Cu/CoFeAl channel
Spin signal shows the significant reduction but is still detectable.
Cu channel Cu/CoFeAl channel
@RT
H (Oe)
R(m
W)
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Spin signal modulation due to anisotropic spin absorption
A
B
C
D
RS
RM
A
B
C
D
ฮ๐ M
(ฮ๐ ๐ 2)ร100 = 43.2%
Modulation efficiency
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Summary
1. Spin polarization improves not only the generationefficiency but also the injection efficiency.
2. CoFe-based alloy is an excellent material for the electricaland thermal spin injection because of its favorable bandstructure.
3. Superconductor is found to be a insulator for spin current.
4. Anisotropic spin absorption has been demonstrated.