1

Gerrit E.W. Bauer

x Institute for Materials Research, Sendai &

Kavli Institute of NanoScience Delft

Xingtao Jia, Kai Liu, Ke Xia(Beijing Normal University)

Material-dependent spin caloritronics

Arne Brataas, Yaroslav Tserkovnyak, Moosa Hatami, Jiang Xiao, Sadamichi Maekawa, Saburo Takahashi, Eiji Saitoh, Ken-ichi Uchida,

Ke Xia, Xingtao Jia, Kai Liu

Contents

Spin Seebeck effect in magnetic insulators

Experiments: Uchida et al. (2010/2011),Theory: Xiao et al. (2010),

Adachi et al. (2010), Ohe et al. (2011)

Spin current detection by inverse spin Hall effect

Experiment

Uchida et al. (2010/2011)

V [

V]

Current-induced spin-transfer torque

N F

0FSI N

SI

y

z

Rˆ m2

e Iˆ

NS

N Ng g

T I

z x

spin-mixing conductance

*F

nm nmnm

g N r r

↑ ↓

spin accumulation

m

Spin currents cause magnetization motion(spin transfer torque, Slonczewski, 1996).

Spin torque and spin pumping

Magnetization motioncauses spin currents(spin pumping, Tserkovnyak, 2002).

Onsagerreciprocals

↑↓

2

Theory by Xiao et al. (2010)

coherence volume near to contact

local non-equilibriumspin mixing conductance

2

M eB rs F N

s coh

k gJ T TM V

pump J-N noises s sJ J J

Foros et al. (2005)

FMR spin pumping experiments

Czeschka et al. (2011)

Scaling as a function of -wave intensity

Uchida et al.

Howard Phillips Lovecraft

YIG (the Father of Serpents), a Great Old One of the CthulhuMythos

YIG: Yttrium Iron Garnet

Y3Fe2(FeO4)3

- 80 atoms/primitive unit cell- ferrimagnetic insulator- Curie temperature 550 K- Gilbert damping ~10-4–10-5

YIG band structure Jia et al., EPL (2011)

0.33eVGGAgE

1.4 eVUgE

Mixing conductance

Heinrich et al., Azevedo et al., Goennenwein et al., MMM 2011

spin current absorption

3

Contents Thermal magnetization torques

T(Pulsed laser) heating

T+T

Q

Heat current induced magnetization dynamics:

Theory:- spin valves: Hatami et al. (2007), Slonczewski (2010).- domain walls: Kovalev & Tserkovnyak (2010,2011), Bauer et al. (2010)

Hals et al. (2010), Hinzke & Nowak (2011), Yan & Wang (2011)

- tunnel junctions: Jia et al. (2011)Experiment (spin valves): Yu et al. (2010).

Magnetic tunnel junctions

Fe () | MgO | Fe (/)

TMR

1000%

AP P

P

R RR

1 nm

MgO CoFeB

Walter et al. (2011); Liebing et al. (2011)

7 ML MgO10 ML MgO

Sample configuration

Fe | MgO | Fe (001)

3 ML MgO ~ 6 Å

300K 7K

300K 60K

AP Pc

P APc

T

T

energy-dependent torkance

Energy-dependent torkancesinterface states

4

Numbers

301 K 300 K

V1k

open circuit301 K 300 K

I1k

closed circuit

Magnetoheatresistance

Contents Q-Noise

Beenakker and Schönenberger, Physics Today, May 2003

Scattering theory

t

tr‘“transmission matrix†T t t

matrix of transmissioncoefficients at the Fermienergy

1

0

Tr

nsns

eIhe eT T TdTh h

T Landauer-Büttiker formula

Tnsns

T T distribution function of transmission matrix eigenvalues

Electronic noise

( ) ( )I t I t I

1

0

20 1 2eS P T T dT eF Ih

T

(0) ( ) i tP I I t e dt

Common wisdom for tunnel junctions:

1

0

21 : 2 1neT S TdT e I FTh

Fano factor

5

Noise in magnetic tunnel junctions

T. Arakawa et al. (2011)

Noisy magnetic tunnel junctions

2IS eF I

Fano factorExperiments Arakawa et al. (2011) @ 3K (10K)

First-principles theoryLiu et al., arXiv:1111.2681

dMgO = 5 ML

Distribution of transmission eigenvalues

Disorder dependencenon-monotonous

[…] CPA

∆1∆5

symmetries

parallel

Without interface states

EF

anti-parallel

∆1

6

parallel

anti-parallel

With interface states, thick junctions

EF

parallel

anti-parallel

With interface states, thin junctions

EF

Skewness/enhancement of the torque

metallic spin valves(Slonczewski, 1996)

spin accumulationenhanced torque

thin tunnel junctions

multiple scattering between interface states

Contents