1

Current-induced magnetic domain wall motion -Effect of the Dzyaloshinskii–Moriya interaction

on the magnetic domain-wall dynamics-

Institute for Chemical Research, Kyoto University Teruo Ono

2

Collaborators

Kab-Jin Kim, Kohei Ueda, Yoko Yoshimura Institute for Chemical Research, Kyoto University

Yoshinobu Nakatani University of Electro-communications

Hiroshi Kohno Nagoya University

Gen Tatara RIKEN

H. Tanigawa, T. Suzuki, N. Ohshima Renesas Electronics Corporation

S. Fukami, F. Matsukura, H. Ohno Tohoku University

3

3

Institute for Chemical Research Nanospintronics Lab.

4

Magnetic domain-wall (DW) • Boundary between two different magnetization regions

DW motion

MFM image

MOKE image

DW and DW motion

B

e-

Magnetic field-driven DW motioin

Electric current-driven DW motion

5

Prediction of current-induced domain wall motion

Change in spin direction of conduction electron

Rotation of

local magnetic moment

Static domain wall

Domain wall

Current

Conservation of spin angular momentum

Luc Berger Professor Emeritus,

Carnegie Mellon University

J. Appl. Phys. 55, 1954 (1984).

x

mu j

t

mmHm

t

meff

jPeM

gu

s

Bj

2

Adiabatic spin transfer torque

DW motion along electron flow

6

Successive images of DW motion by current pulse injections (7×1011 A/m2, 0.5 µs)

DW position can be controlled by current pulsed.

Phys. Rev. Lett., 92 (2004) 077205. NiFe, w = 240nm, t = 10nm

7

Magnetic Racetrack Memory proposed by IBM

A novel three-dimensional spintronic storage memory

Magnetic nanowires: Information stored in the domain

-Capacity of a hard disk drive -Reliability and performance of solid state memory (DRAM, FLASH, SRAM...)

Courtesy of Stuart Parkin (IBM)

8

Race-track memory Demo. Writing, Shifting, Reading

Applied Physics Express 3 (2010) 073004.

Shift operation (3DWs)

Back & forth operation (2DWs)

Mult-DWs motion with the same velocity as a single DW.

Co/Ni with perpendicular magnetization

9

Mechanisms of current-induced DW motion

(1)DWM by spin transfer torque

Tatara and Kohno, Phys. Rev. Lett. (2004).

(2)DWM by spin Hall torque

Thiaville et al., Europhys. Lett. 100, 57002 (2012).

10

Bloch DW

Energy

<

To drive a DW by current,

spin torque has to overcome the barrier of Neel wall!

DWM by adiabatic spin torque

P

KeJ

B

th2

Tatara and Kohno, Phys. Rev. Lett. (2004).

Neel DW

+ -

DW moves with precessional motion.

Direction of DW motion is along electron flow.

Jth is given by

11

Bloch DW Neel DW

Energy

< + -

+ -

Energy

>

Energy

=

How to prove the intrinsic pinning?

For current-driven DW motion by adiabatic torque, Spin torque has to overcome the barrier of Neel wall!

Spin torque has to overcome the barrier of Bloch wall!

Resulting in Jth minimum

By changing wire width,

(1) Existence of minimum of Jth for DW motion

(2) Change of DW structure from Bloch to Neel

12

Neel Wall

Neel Wall + Bloch Wall

Bloch Wall

Bloch Wall

Bloch Wall

Evidence for intrinsic pinning!

Jth & DW resistance v.s. wire width

Bloch DW Neel DW

Nature Materials 10 (2011) 194.

・Jth minimum

・Change of DW structure

13

Spin Hall torque-driven DW motion

SH

NoSH

No

J

Bloch DW

No spin Hall torque!

No DW motion…

J

14

SH

SH

J J

spin Hall torque on Neel wall!

DW motion…

Spin Hall torque-driven DW motion

15

Heff Heff

Heff

Heff

Chiral Neel wall is necessary!

What is the origin of the chiral Neel wall?

Spin Hall torque-driven DW motion

16

Chiral Neel wall stabilized Dzyaloshinskii–Moriya interaction

Dzyaloshinskii-Moriya interaction (DMI)

HDMI= -D12 • (S1 × S2)

Observation of chiral DW by SPLEEM

Wu, Schmid et al., Nat. Comm. (2013)

17

Co/Ni multilayers

• Perpendicular magnetic anisotropy (interfacial anisotropy btw Co and Ni) • Multilayer only with magnetic materials • High tunneling magnetoresistance (TMR) • Low threshold current with high thermal stability

PRL, 68, 682 (1992) APL, 97, 072513 (2010) Nat. Mater. 10, 194 (2011) Nat. Nanotechnol. 7, 635 (2012) Nat. Comm. 4, 2011 (2013)

Promising material for spintronic application

Effect of the Dzyaloshinskii–Moriya interaction on DW dynamics Co/Ni multilayers with broken structural inversion symmetry

…

Co/Ni multilayer

Insert MgO layer to break structural inversion symmetry

Our sample structure

18

Thickness dependence of current-induced DW motion

-3 -2 -1 0 1 2 30

1

J ( 1012

Am-2

)

PD

W

t = 1.2 nm

t = 2.1 nm

t = 3.0 nm

t = 3.9 nm

t = 4.8 nm

t = 5.7 nm

t = 6.6 nm

t = 7.5 nm

t = 8.4 nm

APEX 7, 053006 (2014).

[electron direction] [current direction]

current flow direction

electron flow direction

Me

ch

an

ism

tra

ns

itio

n

19

Thickness dependence of current-induced DW motion

-3 -2 -1 0 1 2 30

1

J ( 1012

Am-2

)

PD

W

t = 1.2 nm

t = 2.1 nm

t = 3.0 nm

t = 3.9 nm

t = 4.8 nm

t = 5.7 nm

t = 6.6 nm

t = 7.5 nm

t = 8.4 nm

APEX 7, 053006 (2014).

Adiabatic spin transfer torque (STT)

e- Adiabatic STT-driven DW motion

Nat. Mater. 10, 194 (2011).

Spin Hall torque

e- Spin Hall torque-driven DW motion

20

Dzyaloshinskii–Moriya interaction

-3 -2 -1 0 1 2 30

1

J ( 1012

Am-2

)

PD

W

t = 1.2 nm

t = 2.1 nm

t = 3.0 nm

t = 3.9 nm

t = 4.8 nm

t = 5.7 nm

t = 6.6 nm

t = 7.5 nm

t = 8.4 nm

APEX 7, 053006 (2014).

Spin Hall torque + Dzyaloshinskii–Moriya interaction

SH

J

21

Summary

We investigated the DW dynamics in Co/Ni multilayered structure which is promising candidate for spintronic applications.

From the thickness dependence of the DW motion, we found that the DW driving mechanim shows transition from SH torque in thinner layers to adiabaitic STT in thicker layers.

We found that the DMI influences the structure of DW, which gives a crucial effect on the DW dynamics.

We developed several methods to quantify the DMI and estimated the DMI-induced effective field in various thicknesses of Co/Ni multilayers.

Using a real-time detection method, we found that the strength of DMI increases as decreasing the temperature.

Supported by Scientific Research(S) of JSPS and the R&D Project for IC

T Key Technology to Realize Future Society of MEXT.