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Manipulating Exchange Bias by Spin-Orbit Torque
Chih-Huang Lai
Materials Science and Engineering,
National Tsing Hua University, Taiwan
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Outline
[Pt/Co/Pt]
HM/FM/HM
[Pt/Co/IrMn]
HM/FM/AFM
Exchange bias switching
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Effective fields induced by Spin-orbit torque in Pt/Co/Pt
0 1 2 3
-150
-100
-50
0
50
100
150H
L: / (+/-M)
HT: / (+/-M)
H
L(T
) (O
e)
Je(10
7A/cm
2)
Spin Hall effect dominated (ΔHL >> ΔHT)
Huang and Lai, APL, 107, 232407(2015)
Js,top
Js,bottom
- =
less intermixing Severe intermixing
Different interface structure
Appl Phys Lett 100, 142410 (2012).
Pt (2 nm)/ Co (0.9 nm)/ Pt (2 nm)/
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SOT in Pt/Co/IrMn
[Pt/Co/IrMn]
HM/FM/AFM
Exchange bias switching
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External magnetic field
AFM
FM
Exchange bias of FM/AFM
1. Deposition with external magnetic field.
External magnetic field
AFM
FM
2. Field-cooling
• Align the interfacial spins of AFM with FM magnetization
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Magnetic property of as-deposited film
Ta 2.5
Pt 2Co 1.2
IrMn 8
Pt 4
Ta 2.5
IrMn
Co Magnetic domain
Interfacial spin
H (Oe)N
orm
aliz
ed M
(M
/Ms)
-2000 -1000 0 1000 2000
-1.0
-0.5
0.0
0.5
1.0
As-deposited film
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SOT switching curve
Device: 5×10 μm2 Hx= 300 Oe
Ta 2.5
Pt 2Co 1.2
IrMn 8
Pt 4
Ta 2.5
Js
-8 -6 6 8-1
0
1
-8 -6 6 8-1
0
1
-8 -6 -4 4 6 8-1
0
1
-8 -6 -4 4 6 8-1
0
1
-8 -4 0 4 8-1
0
1
-8 -4 0 4 8-1
0
1
Kerr
Inte
nsity (
M/M
S)
J (107A/cm
2)
HX = 300 Oe HX = -300 Oe
N=1 N=1
N=2 N=2
N=4 N=4
Ta 2.5
Pt 2Co 1.2
Pt 4
Ta 2.5
Ipulse=20 ns-10 us
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0.0 0.5 1.0 1.5 2.0
-40
-20
0
20
40
H
L (
Oe)
J (107 A/cm2)
Dominant spin current source
0 2 4 6 8 10
-20
-10
0
10
20
a (
10
2O
e/1
07A
/cm
2)
IrMn thickness (nm)0 2 4 6 8 10
IrMn thickness (nm)
-4
-2
0
2
4
β (
10
^4
A/O
e*c
m^2
)
-8 -6 -4 -2 0 2 4 6 8
Je (10^7 A/cm^2)
-1.5
-1
-0.5
0
0.5
1
1.5
Ke
rr I
nte
nsity (
a.u
.)
-4 -2 0 2 4
Je (10^7 A/cm^2)
-3
-2
-1
0
1
2
3
4
Ke
rr In
ten
sity (
a.u
.)
Je (107 A/cm2)
0 2 4 6 8 10
IrMn thickness (nm)
-4
-2
0
2
4
β (
10
^4
A/O
e*c
m^2
)
-8 -6 -4 -2 0 2 4 6 8
Je (10^7 A/cm^2)
-1.5
-1
-0.5
0
0.5
1
1.5
Ke
rr In
tensity (
a.u
.)
-4 -2 0 2 4
Je (10^7 A/cm^2)
-3
-2
-1
0
1
2
3
4
Kerr
Inte
nsity (
a.u
.)
Je (107 A/cm2)
SOT efficiency α=HK/JcHK :anisotropy field Jc :threshold current density
IrMn = 0 nm
IrMn = 4 nm
6 nm8 nm10 nm
Ta 2.5
Pt 2Co 1.2
IrMn t
Pt 4
Ta 2.5
Js
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Current-pulse-induced EB switching
tIrMn=8nmInitial EB
After -I SOT switching
After +I SOT switching
Lin and Lai, Nature Materials, 18, 335 (2019)
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Dominant spin current source- bottom Pt
Ta 2.5
Pt 2Co 1.2
IrMn 8
Pt 4
Ta 2.5
Ti 2.5
Pt 2Co 1.2
IrMn 8
Ti 5
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Joule heating effect?
Sub.//Ti(5)/Pt(5)/[Co(0.3)/Ni(0.6)]2/FeMn(10)/Ti (2)
Co/Ni
FeMn
Pt
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Joule heating effect?
Co/Ni
FeMn
Cu
-1 0 1
-1
0
1
Kerr
inte
nsity (
a.u
.)
H (kOe)
Cu-FeMnHz
Sub.//Ti(5)/Pt(5)/[Co(0.3)/Ni(0.6)]2/FeMn(10)/Ti (2)
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Joule heating effect?
Co/Ni
FeMn
Cu
-1 0 1
-1
0
1
Kerr
inte
nsity (
a.u
.)
H (kOe)
Cu-FeMn
Sub.//Ti(5)/Pt(5)/[Co(0.3)/Ni(0.6)]2/FeMn(10)/Ti (2)
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Jc~ 3*107 A/cm2
Joule heating effect?
20 40 60 80 100 120 140 160 180
-600
-500
-400
-300
-200
-100
0
HEB
(Oe)
T (℃)
TB ≈ 150℃
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Measurement of device temperature
Keithley 4200-SCS (Semiconductor Characterization System) with 4225-PMU Ultra Fast I-V Module
Pulse width = 10 us.Current pulse amplitude =Jc
Time-resolved resistance measurement (TRRM)
Δ𝑅 = 𝑅 − 𝑅0𝑇 = 𝑇0 + 𝛾 ∆𝑅 =
𝛾 = 12.27 K/Ω ,where γ=dT/dR
67.5 ±1.7℃
Pt 2/Co 1.2/IrMn 6 (nm)
0 2 4 6 8 10 12 14
0
1
2
3
4
25
37
50
62
74
T
(oC
)Time (s)
R
(
)
0 10 20 30 40 50
0
1
2
3
4
25
37
50
62
74
T
(oC
)
Time (s)
R
(
)
10 𝜇𝑠 10 𝜇𝑠
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Effects of Hx on SOT switching of FM and EB
AP-mode
The reversal of interfacial spins depends on FM magnetization, regardless of Hx.The spin current provides disturbance for the interfacial spins to be aligned with FM.
Co/Ni
IrMn
Pt
Hysteresis loop
+IHx = 0 Oe -I
+I, Hx = 300 Oe
-I, Hx = 300 Oe
# SOT switching, Hx=300 Oe
Initial FM state
Final FM state
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How far can spin current go through the FM
For ferromagnetic layer thickness > 3.4 nm, the EB is not switched
Ti
Pt 2
Co/Ni t
IrMn 8
Ti
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Enhanced spin torque at FM/AFM interface
current
Phys. Rev. B 73, 054428 (2006).
𝜕𝒎
𝜕𝑡= −𝛾𝒎 ×𝑯eff + 𝛼 ෝ𝒎 ×
𝜕𝒎
𝜕𝑡−𝛿𝒎
𝜏− 𝛻 ∙ 𝑸
JsCo
IrMn
Pt
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SOT switching in AP-mode
Pt(2)/ [Co(0.2)/Ni(0.8)]2/IrMn(8)
The closeness of FM and EB switching thresholds provides an indirect hint that SOT is the key for the switching mechanism.Flipping interfacial spins is accumulative and leads to smooth EB reversal, different from FM reversal.
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Independent SOT switching of ferromagnetic
magnetization and exchange bias.
FM: No changeEB: Change
FM: ChangeEB: No change
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Field-free switching
→ after In-plane annealing, the field free SOT switching can be accomplished
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Summary
Current pulse-induced EB switching
SOT does not only switch FM but interfacial AFM
Nat. Mater. 18, 335 (2019)
Joule heating is not a major factor
Temperature rise is muchlower than TB
SOT effects on FM and AFM are different
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Acknowledgement
• Dr. Kuo-Feng Huang
• Dr. Ding-Shou Wang
• Mr. Po-Hung Lin
• Prof. Hsiu-Hau Lin( Physics, NTHU)
• Funding supported by Ministry of Science and Technology (MOST), Taiwan
and Applied Materials Co.
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Thank you for your attention!
Chih-Huang Lai
Web page of our lab:Prof. Chih-Huang Lai