1

Manipulating Exchange Bias by Spin-Orbit Torque

Chih-Huang Lai

Materials Science and Engineering,

National Tsing Hua University, Taiwan

2

Outline

[Pt/Co/Pt]

HM/FM/HM

[Pt/Co/IrMn]

HM/FM/AFM

Exchange bias switching

3

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)/

4

SOT in Pt/Co/IrMn

[Pt/Co/IrMn]

HM/FM/AFM

Exchange bias switching

5

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

6

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

7

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

8

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

12

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

chlai@mx.nthu.edu.tw

Web page of our lab:Prof. Chih-Huang Lai