spintronics in metals and...

Spintronics in metals

Tomas Ju

Institute of Physics ASCRAlexander Shick, Karel Výborný, Jan Zemen,Jan Masek, Vít Novák, Kamil Olejník, et al.

Hitachi CambridgeJorg Wunderlich Andrew Irvine David WilliamsJorg Wunderlich, Andrew Irvine, David Williams

Elisa de Ranieri, Byonguk Park, Sam Owen, et a

and semiconductors

ngwirth

University of NottinghamBryan Gallagher, Tom Foxon,

Richard Campion, Kevin Edmonds,Andrew Rushforth Chris King et alAndrew Rushforth, Chris King et al.

sTexas A&M

Jairo Sinova et als, al. University of Texas

Allan MaDonald, et al.

Jairo Sinova, et al.

OuOu

11.. Tunneling anisotropic magnetoresTunneling anisotropic magnetores

2 F ti i (G M )A2 F ti i (G M )A2. Ferromagnetism in (Ga,Mn)As an2. Ferromagnetism in (Ga,Mn)As an

3. Spintronic transistors3. Spintronic transistors3 Sp o c a s s o s3 Sp o c a s s o s

utlineutline

sistance in transition metalssistance in transition metals

d l t d i d td l t d i d tnd related semiconductorsnd related semiconductors

Spintronics: Spin-orbit & enucleus rest frame electronnucleus rest frame electron

vI Q= rE 304 r

Qπε

=4

B =πμ

S ⋅= B2

gH BSO

h

μ⇒ spin-orbit interaction

Coulomb repulsion & Pauli exclusion prinCoulomb repulsion & Pauli exclusion prin

exchange interactions

n rest frame Th in rest frame Thomas precession

30

rrI×

πμ

EvEvB ×=×=⇒ 2001c

εμ

EvS ×⋅= 22B

mce

DOS

nciple ⇒ exchange interactionnciple ⇒ exchange interaction

⇒ ferromagnetism

AMRAMR~ 1% MR effect~ 1% MR effect

Mr

Exchange int.:

) vs.( ~ IMvg

rrτσ

)(BMrr

Spin-orbit int.:

magnetic anisotropy

TAMRTAMR

)(

)(OSr

Au

)(MTDOS

TMRTMR~ 100% MR effect~ 100% MR effect

Exchange int.:

)()( ↑↑<↑↓ TDOSTDOS )()(AFM-FM exchange bias

TAMR in

ab intio theoryShick, et al, PRB '06, Park, et al, PRL '08

CoPt structures

experimentPark, et al, PRL '08

TAMR in TM structures

spontaneous moment

Proposal for AFM TAMR: first microelectrProposal for AFM-TAMR: first microelectr

Consider uncommon TM combinationsMn/W → ~100% TAMR Shick, et al,

Consider both Mn-TM FMs & AFMs

unpublished

exchange-spring rotation of the AFMScholl et al. PRL ‘04

ronic device with active AFM componentronic device with active AFM component

Shick, et al,unpublishedunpublished

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TM-based → semiconductinsensors & memories

Magnetic spintronic magp gmemories

Ferroelectrics/piezoelectrics

electro-mechanical transducors, large & persistent el. fields

ng multiferroic spintronics→ transistors & logicg

materialsgneto-sensors, g ,

Semiconductors

transistors, logic,sensitive to doping and p gelectrical gating

Ferromagnetic sNeed true FSs not FM inclusio

GaAs GaAs -- standard IIIstandard III--V semV sem

GG IIII MM dil tdil tGroupGroup--II II Mn Mn -- dilute dilute magnmagn& holes& holes

(Ga Mn)As(Ga Mn)As feferrromagnetiromagneti(Ga,Mn)As (Ga,Mn)As -- feferrromagnetiromagnetisemiconductsemiconduct

semiconductorsons in SCs

Ga

AsMn

miconductormiconductor

titi ttMn

As

eticetic moments moments

cccctortor

E↓

GaAs:Mn – extrinsi

EFspin ↓

1% M 1% Mn

DO

S << 1% Mn ~1% Mn

spin ↑As p like holes localized on Mn a

Asvalence band As-p-like holes

As-p-like holes localized on Mn a

As-FM due to p-d hybridization(Zener local-itinerant kinetic-exchange)

Mn-d-limom

ic p-type semiconductor

Energy

>2% Mn

gy

acceptorsonset of ferromagnetism near MIT

p like holesGa

Mn

acceptors

-p-like holesAs

Mn

ike localments

(Ga,Mn)As

L

H

high-T growth

H

→

Inco→

optimal-T growth

synthesis

ow-T MBE to avoid precipitation

High enough T to maintain 2D growthHigh enough T to maintain 2D growth

→ need to optimize T & stoichiometryfor each Mn-dopingfor each Mn doping

nevitable formation of interstitial Mn-donorsompensating holes and momentsp g→ need to anneal out

Interstitial Mn out-diffusiPolyscrystalline20% shorter bonds

OGaMnAs-oxide

GaMnAsMnI

++

10x shorther annealing with etch

O((is

ion limited by surface-oxide

x-ray photoemission

Olejnik et al, ‘08

Optimizing annealing time & temperature removing int Mn & keeping Mn in place)removing int. Mn & keeping MnGa in place) s essential Rushforth et al, unpublished

Tc limit in (Ga,Mn)As remains ope

Indiana & California (‘03): “ .. Ohno’s ‘98 T =110 K is the fundamental upper limit ”Tc 110 K is the fundamental upper limit .. Yu et al. ‘03

California (‘08): “…Tc =150-165 KCalifornia ( 08): …Tc 150 165 K independent of xMn>10% contradicting Zener kinetic exchange ...”

Mack et al ‘0Mack et al. 0

“Combinatorial” approach to growthwith fixed growth and annealing cond.

160

180

en

80

100

120

140

(K)

20

40

60

80

T C Nottingham & Prague (’08): Tc up to 188 Kso far

0 1 2 3 4 5 6 7 8 9 100

Mntotal(%)

?08 ?08

Mean-field butlow Tc

MF

Large TcMF but

low stiffness

(Al,Ga,In)(As,P) good candidates, Ga

Other (III,Mn)V’s DMSs

Kudrnovsky et al. PRB 07

W k h b id Delocalized holes

y

Weak hybrid. Delocalized holeslong-range coupl.

InSbd5

t

Strong hybrid.Impurity-band holesshort-range coupl.

t

GaP aAs seems close to the optimal III-V host

III = I + II → Ga = Li + Zn

Other DMS candidates

GaAs and LiZnAs

(Ga,Mn)As and L

should be twin fe

But Mn isovalent

→ no Mn concen

ibl b th→ possibly both

(Li / Zn stoich

n

s

s are twin SC

Li(Zn,Mn)As

erromagnetic SC

Masek et al. PRL 07t in Li(Zn,Mn)As

ntration limit and self-compensation

t d t f ti SCp-type and n-type ferromagnetic SC

hiometry)

Towards spintronics in (Ga,Mn)As

Dense-moment MSλ << dλF<< d↑-↑

Eu↑ - chalcogenides

Critical contribution to resistivity at Tc~ magnetic susceptibility magnetic susceptibility

s: FM & transport ↑

Dilute-moment MSλF~ d↑ ↑λF d↑-↑

Broad peak near Tc disappeares with annealing (higher uniformity)???annealing (higher uniformity)???

Critical contribution at

Fe

NiFisher & Langer ’68

dρ/dT ~ cv

Tc to dρ/dT like TM FMs

(Ga,Mn)As (Prague Nottingham)(Prague Nottingham)

Novak et al., ‘08

λF ~ d↑-↑

~),(~)( 2Γ JTRT pdi

rρ

⟩⟨Γ 2)(~ Suncor

rsmalluncor →Γ Tc

EuCdSe

MFΓ

χ~)0~~( FkkΓ

][ 00 ⟩⟨⋅⟩⟨−⟩⋅⟨ SSSS iid

rrrr

0=k1<<↑−↑kd

1~↑−↑kd

)/1~~( ↑−↑Γ dkk F

NivcdTddTd ~/~/ Γρ

Tc

Ferromagnetism & stroG

Mn

As-p-like holes

drdV

err

mcp

mcSeBH effSO

rrr

⎢⎣

⎡⎜⎝⎛×⋅⎟⎟

⎠

⎞⎜⎜⎝

⎛−=⋅−= μ (1

Strong SO due to the As p-shell (L=1) chara

Beff Bex + Beff

ong spin-orbit couplingGa

MAs

Mn

n

pss

LSrr rr

⋅=⎥⎦

⎤⎟⎠⎞ α)( ∇V

BBeffeff

ss

acter of the top of the valence band

BBeffeff

TAMR discovered in (Ga,Mn)As Gold et al. PRL’04

SCAMR in DMSs C

~

magnetic. only

~

>>max AMR

SO couped carries scattering coherently off Coulomb & polarized-magnetic potential of MnCou o b & po a ed ag et c pote t a o

MnGa

sign and magnitude (numerical) consistent with experiment

Remark: Extraordinary MRs & qua

dirty metal

ntum coherent transport phenomena

UCFUCF

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Gating of the highly doped

3]

1019

cm-3

dens

ity[

carr

ier

(Ga,Mn)As: p-n junction FET

10

]

p-n junction depletion estimates

6

8 0V 3V10

cm

2

4 5V 10V

dens

ity [

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0

2ca

rrie

r

GaMnAs layer thickness [nm]

~25% depletion feasible at low voltages

Olejnik et al., ‘08

VV

Increasing ρ and decreasing AM

19.2

19.4

m]

V

18.8

19.0

19.2

ρ [1

0-3Ω

cm

20 22

18.6

1.02)

MR

098

1.00

B)/R

(B=0

)

AM

0.96

0.98

R(B

-400

Vg = 0VV 3V

MR, Tc, coercivity with depletion

24.0

24.5Vg = 3V

0

100

6 Ω

-100

0

230

23.5 -100

dρ/d

T [1

0-6

-200

100

24 26 28 30 32 34T [K]

22.5

23.0

20 22 24 26 28 30 32 34

-200

d

T [K]

-300

T [K] T [K]

Vg [V] -1.0

300

e] 0.0 1.0 2.0 2.530

200

250

e fie

ld [O

e

3.0 3.5

150

200

coer

cive

-200 0 200 400B [Oe]

-1 0 1 2 3 4Vg[V]

Persistent variations of magnetic p

200

65K62K depletionaccumulation

dR/d

T

100

d

30 40 50 60 70 80 90 100T (K)

properties with ferroelectric gates

Stolichnov et al., ,Nat. Mat.‘08

n

Electro-mechanical ga

Strain & SO →

Electrically controlled

ating with piezo-stressors

exy = 0.1%exy = 0%

Rushforth et al., ‘08

magnetic anisotropies

(Ga,Mn)As spintronic

Wunderlich et a

Huge, gatable, and

Single-electron transistor

Huge, gatable, and

single-electron transistor

al. PRL ‘06

d hysteretic MRd hysteretic MR

Two "gates": electric and magnetic

AMR nature of t

normal AMR

the effect

Coulomb blockade AMR

Single-electron charging ene

Source DrainVD

Q

GateVG

∫Q

'' M(Q)Q(VdQUr

μΔ

20 )QQ( r+

∫ +=0

D e(Q)Q(VdQU μ

MGG00 )]M(VV[CQ&

C2)QQ(U

Σ

+=+

=

electric && magnemagnecontrol of Coulomb blockade o

ergy controlled by Vg and M

QQindind = = nnee

QQindind = (= (n+1/2)n+1/2)eeQ0

Q0

ΔECe2/2CΣ

n-1 n n+1 n+2n-1 n n+1 n+2

)

C)M(μΔr

)[010]

Φ

M[110]

[100]

GM C

Ce

)M(V&)] ΣμΔ= [100]

[110][010]

eticeticoscillations

[0 0]

SO-coupling →μ(M)

Theory confirms chemical potenti& predicts CBAMR in SO-coupled& predicts CBAMR in SO coupled

al anisotropies in (Ga,Mn)Asd room-T metal FMsd room Tc metal FMs

•• CBAMRCBAMR ifif changechange ofof ||ΔμΔμ((MM)|)| ~~ ee22//22CCΣΣ

•• InIn ourour (Ga Mn)As(Ga Mn)As ~~ meVmeV (~(~ 1010 Kelvin)Kelvin)•• InIn ourour (Ga,Mn)As(Ga,Mn)As ~~ meVmeV (~(~ 1010 Kelvin)Kelvin)

•• InIn roomroom--TT ferromagnetferromagnet changechange ofof||ΔμΔμ((MM)|~)|~100100KK||ΔμΔμ((MM)|)| 100100KK

• Room-T conventional SET(e2/2CΣ >300K) possible(e /2CΣ 300K) possible

Nonvolatile progr

Variant p- or n-type FET-like transistor in

VDD

1VA VB

0 0OFFON OFF

1 0OFF

0ON

11ON

1ON

VB

V0

ON

0 01

OFF

1 11

OFF

1

VA

ON

01ONOFFON

0OFF

1OFF

OFF

“ORONOFF OR

rammable logic

one single nano-sized CBAMR device

0 1

ONOFF

0 10

ON OFF

1

Vout

A B Vout0 0 01 0 10 1 1R” 0 1 11 1 1

R

Nonvolatile progNonvolatile prog

Variant p- or n-type FET-like transistor in

VDD

VA VB

VB

V

VA “OROR

grammable logicgrammable logic

one single nano-sized CBAMR device

0 1

ONOFF

0 10

ON OFF

1

Vout

A B Vout0 0 01 0 10 1 1R” 0 1 11 1 1

R

Physics of SO &Device design

Chemical pC

SET→ CBA

Tunneling→ TAM

Tunneling device

→ TAM

G l itResistor

Group velocity → AMR

& exchange Materials

potentialTM FMsAMR TM FMs,MnAs, MnSb

(III,Mn)V, I(II,Mn)VDMSs

g DOS MRMR

Mn-based TM FMs&AFMs

& lif ti TM FM& lifetime R

TM FMs

spintronics in metals and...

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