Présent et futur de la spintronique LAAS, 17/12/ 08 TMR, etc … Spintronics. Spin ... Other...

Influence of spin on conduction

Magnetic nanostructures

Memory (M-RAM)

GMR, TMR, etc…

Spintronics

Spin up electron

Spin down electron

Spin transfer :

- writing by electrical transport of magnetic

information,

- microwave generation

spintronics with semiconductors,

molecular spintronics,

Single-electron spintronics, etc

Présent et futur de la spintronique (LAAS, 17/12/ 08)

spin

charge

électron

Introduction :

Spin dependent conduction in

ferromagnetic conductors,

Giant Magnetoresistance (GMR),

Tunnel Magnetoresistance (TMR)

E

EF

n (E)

n (E)

Spin dependent conduction in ferromagnetic metals (two current model)

Mott, Proc.Roy.Soc A153, 1936

Fert et al, PRL 21, 1190, 1968

Loegel-Gautier, JPCS 32, 1971

Fert et al,J.Phys.F6, 849, 1976

Dorlejin et al, ibid F7, 23, 1977ρ

ρ

I

I α= ρ↓

/ ρ↑

or β

= (ρ↓

-

ρ↑

)/ (ρ↓

+ ρ↑

) = (α

- 1)/(α

+ 1)

E

EF

n (E)

n (E)

Ni d bandCr d↑

level

Virtual boundstate

Cr d↓

level

Ni d band

α ≈ 0.3

α ≈ 20

Ti V Cr Mn Fe Co Ni

ρ↓

ρ↑

α= ρ↓

/ ρ↑

Mixing

impurities

A and B with

opposite or similar

spin asymmetries: the pre-concept of GMR

Example: Ni + impurities A and B (Fert-Campbell, 1968, 1971)

1st case 2d case αA > 1, αB < 1 αA and αB > 1

High mobility channel low ρ

ρAB >> ρA + ρB ρAB ≈ ρA + ρB

spin

spin

spin

spin

J. de Physique 32, 1971

α

= ρ↓

/ρ↑

Fe

Fe

Cr

Cr

• Magnetic multilayers

Fe

Fe

Fe

Cr

Cr

Magnetizations of Fe layers at zero fieldin Fe/Cr multilayers


Fe

P. Grünberg, 1986 →

antiferromagnetic interlayer coupling

Fe

Fe

Cr

Cr

Magnetizations of Fe layers in an

applied fieldin Fe/Cr multilayers


Fe

H

P. Grünberg, 1986 →

antiferromagnetic interlayer coupling

~ + 80%

• Giant Magnetoresistance (GMR)(Orsay, 1988, Fe/Cr multilayers, Jülich, 1989, Fe/Cr/Fe trilayers)

Resistance ratio

Magnetic field (kGauss)

AP (AntiParallel) P (Parallel)Current

V=RI

Orsay Jülich

~ + 80%

• Giant Magnetoresistance (GMR)(Orsay, 1988, Fe/Cr multilayers, Jülich, 1989, Fe/Cr/Fe trilayers)

Resistance ratio

Magnetic field (kGauss)

Anti-parallel magnetizations (zero field, high resistance)

CrFe

Fe

Parallel magnetizations (appl. field, low resist.)

CrFe

Fe

Condition for GMR: layer thickness ≈

nm

AP (AntiParallel) P (Parallel)Current

net current

track

Read head of hard disc drive

GMR sensor5 nm

Magnetic

fields generated

by the media

0

1997 (before GMR) : 1 Gbit/in2 , 2007 : GMR heads ~ 600 Gbit/in2

voltage

current

Recent review : « The emergence of spintronics in data storage »

Chappert, AF et al Nat. Mat.(Nov.07)

STT-RAM (in demonstration)

with MgO tunnel junctions

+ writing by spin transfer

Applications: - read heads of Hard Disc Drive

- M-RAM (Magnetic Random Access Memory) and STT-RAM

~ 100 nm

• Magnetic Tunnel Junctions,Tunneling

Magnetoresistance

(TMR)

Low resistance state High resistance state

ferromagneticelectrodes

tunnelingbarrier

(insulator) APP

Moodera

et al, 1995, Miyasaki

et al,1995,

CoFe/Al2

O3

/Co, MR ≈30-40%

Jullière, 1975, low T, hardly reproducible

≈

0.1 μm

CoFeB/MgO/CoFeB, ΔR/R

≈

500% at

RT in 2006-2007

aims: density/speed of DRAM/SRAM + nonvolatilty

+ low

energy

consumption

MRAM (2006, Freescale)

First examples

on Fe/MgO/Fe(001): CNRS/Thales (Bowen, AF et al, APL2001)

Nancy (Faure-Vincent et al, APL 2003) Tsukuba

(Yuasa

et al, Nature Mat. 2005)

IBM (Parkin

et al, Nature Mat. 2005) ….etc

Epitaxial magnetic tunnel junctions (MgO, etc)

Yuasa et al, Fe/MgO/Fe Nature Mat. 2005

ΔR/R = (RAP

-RP

)/ RP ≈

200% at

RT

CoFeB/MgO/CoFeB,

ΔR/R ≈

500% at

RT in several laboratories

in 2006-2007

Clearer picture of the physics of TMR:

what is inside the word « spin polarization »?

+2006-2007

Mathon and Umerski, PR B 1999 Mavropoulos et al, PRL 2000 Butler et al , PR B 2001 Zhang and Butler, PR B 2004 [bcc Co/MgO/bcc Co(001)]

P

AP Δ1

Δ2’

Δ1

Δ5

Δ5Δ2’

Tunneling from to

spin ↑

state (majority spin) of symmetry Δ1

at EF

spin ↑


at EF

P

spin ↑


at EF

With reversed M in the right electrode,

spin ↑ corresponds to a

minority spin band state without Δ1 character at E F

in which the tunneling Δ1 el.

cannot be accomodated

AP

Common physics:

spin accumulation

spins injected to long distances

by diffusion

Spin Transfer (magnetic switching, microwave generation)

Spintronics with semiconductors

Spintronics with molecules

0

2

4

6

8

10

0 100 200 300 400 500

Co thickness (nm)M

R ra

tio (%

)

400 nm

Co/Cu: Current ⊥ to Plane (CPP) -GMR of multilayered nanowires (L.Piraux, AF et al, APL 1994,JMMM 1999)

CIP-GMR

scaling length = mean free path

CPP-GMR

scaling length = spin diffusion length >> mean free path

spin accumulation theory (Valet-Fert, PR B 1993)

100 nm

Other results: MSU group, PRL 1991, JMMM 1999

CPP-GMR subsists at almost 1μm

F Ms fl = spin diffusion length

in FM

= spin diffusion length

in NMN Ms fl

Spin injection/extraction at a NM/FM interface (beyond ballistic range)

NM FM

zone of spin accumulation

NMsfl FM

sfl

EF↑

EF↑

= spin↑

chemical potential

Spin accumulation Δμ= EF↑

-EF↓

Spin current = J↑

-J↓

z

z

EF↑

-EF↓

~ exp(z/ ) in FMF Ms fl

EF↑

-EF↓

~ exp(-z/ ) in NMN Ms fl

N Ms fl FM

sfl

EF↓

= spin↓

chemical potential

E

J↑

-J↓

J↑

+J↓

= current spin polarization

(illustration in the simplest case = flat band, low current,

no interface resistance, single polarity)

(example: 0.5 μm in Cu, >10μm in carbon

nanotube)

F Ms fl = spin diffusion length

in FM

= spin diffusion length

in NMN Ms fl

Spin injection/extraction at a NM/FM interface (beyond ballistic range)

NM FM


NMsfl FM

sfl

EF↑

EF↑


-EF↓

Spin current = J↑

-J↓

z

z

N Ms fl FM

sfl

EF↓

E

(illustration in the simplest case = flat band, low current,

no interface resistance, single polarity)

Description*

: Boltzmann-type formalism

with the distribution function associated

to a spin

and position dependent

chemical pot. which leads

to

macroscopic equations**

relating the

charge and spin currents to a

spin dependent

electro-chemical potential

μσ

(z)= eV(z) + EFσ

(z)

CPP-GMR: multi-interface with interface resistances. Semiconductors: new problems with band bending, large currents, “conductivity mism.” Spin torque: non-colinear situation

*Valet and Fert, PR B 48, 7099, 1993.

** similar equ. in Silsbee-Johnson and van Son et al

)(zEFσ

NM

= metal

or semiconductor

FM


NMsfl FM

sfl

EF↑

EF↑


-EF↓

Spin current = J↑

-J↓

z

z

N Ms fl FM

sfl

EF↓

E

NM= metal

Semiconductor/ F metal

If similar

spin spliting

on both

sides

but much

larger

density

of states in F metal

much

larger

spin accumulation density

and much

more spin flips

on magnetic

metal

side

almost

complete

depolarization

of

the current

before

it

enters

the SCNM = semiconductor

1) situation without interface resistance

(« conductivity mismatch »)

(Schmidt et al, PR B 2000)

Spin injection/extraction at a Semiconductor/FM interface

NM

= semiconductor

EF↑

Rasbah, PR B 2000 A.F-Jaffrès, PR B 2001


-EF↓

N Msfl FM

sflz

EF↑

Current Spin Polarization

(J↑

-J↓

)/(J↑

+J↓

)

FM spin dependent. interf. resist. (ex:tunnel barrier)

EF↓

EF↑

Spin dependent drop of the electro-chemical potential

Discontinuity increases the spin accumulation in NM

re-balanced spin relaxations in F and NM

extension of the spin- polarized current into the

semiconductor

e-

NsfNNb lrr ρ=≈*

NsfNNb lrr ρ=>>*

Spin injection/extraction at a Semiconductor/FM interface

J↑

-J↓

J↑

+J↓*

*

bNF

bFrrr

rr++

+=

γβDeviations from at large current density (drift effect)

= low current limit

current density

= deviations

from the low

current

limit

(nondegenerate semiconductor)

from Jaffrès and A.F.

(see also Yu and Flatté)

(tranport of magnetization by an electrical curent)

- fundamentals

-

switching of magnetization by spin transfer and applications (STT-RAM, reprogrammable devices)

- microwave oscillations by spin transfer and applications to telecommunications.s

-

Spin transfer

Spin transfer(J. Slonczewski, JMMM 1996, L. Berger, PR B 1996)

S

S≡

Torque on S ≈

Mx(MxM0 )

Ex:Cobalt/Copper/ Cobalt

The transverse component of the spin current is absorbed and transferred

to the total spin of the layer

∝

j M x (M x M0

)

Au

4 nm10 nm

Free magn. layer Cu

Polarizer

Trilayered pillar or tunnel junction

Au

CoFeBMgO

CoFeB

Tunnel junction ≈

50x170 nm²

70 nm

Metallic pillar ≈

50x150 nm²

Au

4 nm10 nm

Free magn. layer Cu

Polarizer

Trilayered pillar or tunnel junction

Metallic pillar ≈

50x150 nm²

x

1) Magnetization switching by spin transfer

2) Sustained precession of the magnetization of the free layer

and generation of radio- frequency oscillations

Two regimes of spin transfer

Applications: writing a memory, etc

Applications: spin transfer nano- oscillators (NSTOs) for

communications (telephone, radio, radar)

Zero or low field

Appl. field

H

Polarizer magnetization

Free layer magnetization

70 nm

Tunnel junction ≈

50x170 nm²

Au

CoFeBMgO

CoFeB

Regime of irreversible magnetic switching

AP

P

H=7 Oe RT

typical switching current ≈

107A/cm2

switching time can be as short as 0.1 ns (Chappert et al)

-2 014,4

14,5

14,6

dV/d

I (Ω

)

I (m A)

-1.0x105 -5.0x104 0.0 5.0x104 1.0x105

400000

450000

500000

550000

Res

ista

nce

(Ω)

Current density (A.cm-2 )

30 K

1 x 105 A/cm2

Py/Cu/Py 50nmX150nm (Boulle, AF et al) GaMnAs/InGaAs/GaMnAs tunnel junction (MR=150%)

(Elsen, AF et al, PR B 2006)

First experiments

on pillars:

Cornell

(Katine

et al, PRL 2000)

CNRS/Thales (Grollier

et al, APL 2001)

IBM (Sun et al, APL 2002) -1.0

-0.50.0

0.51.0

-0.1

0.0

0.1

-1.0-0.5

0.00.5

1.0

Mz

M yMx

APP

m

Py = permalloy

Au

4 nm10 nm

Free magn. layer

Polarizer

Cu

Regime of steady precession (microwave frequency range)

CNRS/Thales, Py/Cu/Py

(Py

= permalloy)

Polarizer magnetization

-1.0-0.5

0.00.5

1.0

-0.5

0.0

0.5

-1.0

-0.5

0.0

0.51.0

mH

Mz

M y

Mx

-1.0-0.5

0.00.5

1.0

-0.5

0.0

0.5

-1.0

-0.5

0.00.5

1.0mH

Mz

M y

Mx

Increasing current

3,5 4,00

1

2

3

Pow

er (p

W/G

Hz)

Frequency (GHz)Microwave power spectrum of the

oscillations of a permalloy-based pillar

-4 014,4

15,0

15,6

dV/d

I (Ω

)

I (mA)

5600G

9G

applied field

Regime of steady precession for tunnel junctions

CoFeB/MgO/CoFeB junction (J.Grollier, AF et al 2008, collaboration S. Yuasa et al, AIST)

4.5 5.0 5.50

30

60

90

PS

D (n

W/G

Hz)

Frequency (GHz)

1.40mALorentzian fit

H = -303G

PSDmax = 90 nW/GHz

width=62MHZ

RT

Tunnel junction ≈

50x170 nm²

Au

CoFeBMgO

CoFeB

Spin Transfer mixes very different (and interacting) problems:

transport (in metallic pillars, tunnel junctions, point contacts)

problems of non-linear dynamics

micromagnetism (non-uniform excitations, vortex motion..)

Au Py (8nm, free)Cu ( 8nm)

Co (8nm, fixed)IrMn (15nm) or CoO or Cu

100x170nm²

Co/Cu/Py (« wavy » angular variation calculated

by

Barnas, AF et al, PR B 2005)

-4 014,4

15,0

15,6

dV/d

I (Ω

)

I (mA)

5600G

9G

Negative I (mA)

Py/Cu/Py (standard)

Positive I

Boulle, AF et al, Nature Phys. 2007 oscillations at H=0

free Py:fast spin relaxation

fixed Co: slower spin relaxation

H ≈

0

Current pulse

Applications of magnetic

switching

by spin transferSwitching of reprogrammable devices (example: STT-RAM)

To replace M-RAM (switching by external magnetic field : nonlocal,

risk of « cross-talk » limiting integration, too large currents)

STT-RAM :«Electronic» reversal by spin transfer from an electrical current

Current pulse

CMOS logic

Embedded STT-RAM

Non volatile FPGA Logic Circuits

Flash and SRAM would be replaced by a non volatile memory (<10F2) embedded directly inside the look

up table (Sony, IEEE Proc. 07)

Applications of magnetic

switching

by spin transferSwitching of reprogrammable devices (example: STT-RAM)

To replace M-RAM (switching by external magnetic field : nonlocal,

risk of « cross-talk » limiting integration, too large currents)

STT-RAM :«Electronic» reversal by spin transfer from an electrical current

Spin Transfer Oscillators (STOs)

(telecommunications, radar, chip to chip communication…)

-Needed

improvements

--

Increase

of power by synchronization of a large number N

of STOs

( x N2 )

-Optimization

of the emission linewidth

Advantages:

-direct

oscillation in the microwave

range (0.5-40 GHz)

-agility: control of frequency

by dc

current

amplitude

- high

quality

factor

-

small

size (≈

0.1μm) (on-chip integration, chip to chip com., microwave assisted writiing in HDD)

f/fΔf ≅ 18000


and molecules

GaMnAs (Tc →170K) and R.T. FS

Electrical control of ferromagnetism

TMR, TAMR, spin transfer (GaMnAs)

Field-induced metal/insulator transition


Magnetic metal/semiconductor hybrid structures

Example: spin injection from Fe into LED

(Mostnyi et al, PR. B 68, 2003)

Ferromagnetic semiconductors (FS)

F1 F2Semiconductor

channel

V

Logic devices, spin transistor ?

Semiconductor lateral channel between spin-polarized source and drain

transforming spin information into large(?) and tunable (by gate voltage)

electrical signal

Nonmagnetic lateral channel between spin-polarized source and drain

Semiconductor channel:

« Measured effects of the order of 0.1-1% have been reported for the change in

voltage or resistance (between P and AP)…. », from the review article

« Electrical Spin Injection and Transport in Semiconductors » by BT Jonker

and ME Flatté in Nanomagnetism (ed.: DL Mills and JAC Bland, Elsevier 2006)

Carbon nanotubes:

ΔR/R ≈

60-70%, VAP -VP ≈

20-60 mV

LSMO LSMO

LSMO = La2/3 Sr1/3 O3

MW-CNT 1.5 μm

L.Hueso, N.D. Mathur,A.F. et al, Nature 445, 410, 2007

F1 F2Semiconductor

channel

PAP

M







Carbon nanotubes:

ΔR/R ≈

60-70%, VAP -VP ≈

20-60 mV

LSMO LSMO


nanotube 1.5 μm


F1 F2Semiconductor

channel

PAP

MR ≈

72%







Carbon nanotubes:

ΔR/R ≈

60-70%, VAP -VP ≈

20-60 mV

AP

P PLSMO LSMO


nanotube 1.5 μm


F1 F2Semiconductor

channel

PAP

60%

AF and Jaffrès PR B 2001 +cond-mat 0612495, +

IEEE Transactions.on

Electronic Devices.

54,5,921,2007

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

sfbn

b

sfnP

rfor

raszerotodrops

RR

ττ

ττγγ

>>∝

+−

=Δ

*

*

22

/1

/1)1/(

Condition

dwell time τn < spin lifetime τsf

Condition for

spin injection

Nb rr /*

vrL

vt

L

timedwell

b

rn

*

*2

∝=τ

ΔR

/RP

1.6

1.2

0.8

0.4

0.0

L=20nmL

L

NsfNN

b

lr

r

ρ

γγ

=

==

∝=

0.8) (calc.withresistance interface theofasymmetry spin

teff1/trans.coresist.interfaceareaunit **r

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

Condition


Condition for

spin injection

Nb rr /*

F1 F2Semiconductor

channel

V

L

F1 F2Semiconductor

channel

V

L

ΔR

/RP

1.6

1.2

0.8

0.4

0.0

L=20nmL

LInterface resistance rb *

in most experiments

Two interface spin transport

problem (diffusive regime)

sfn ττ >>NsflL / Ll N

sf /

Window only for lsf (N) > L

1)( 2 −∝L

lwindow sf

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP


10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

Condition


Condition for

spin injection

Nb rr /*

ΔR

/RP

1.6

1.2

0.8

0.4

0.0

L=20nmL

L10-4 10-2 100 102 104

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

Condition


Condition for

spin injection

Nb rr /*

F1 F2Semiconductor

channel

V

L

F1 F2Semiconductor

channel

V

L

1.6

1.2

0.8

0.4

0.0

L=20nmL

L



vrL

vt

L

timedwell

b

rn

*

*2

∝=τAF and Jaffrès

PR B 2001* +cond-mat 0612495, +

IEEE Tr.El.Dev*. 54,5,921,2007

*calculation. for Co and GaAs

at RT

NsflL / Ll N

sf /

sfbn

b

sfnP

rfor

raszerotodrops

RR

ττ

ττγγ

>>∝

+−

=Δ

*

*

22

/1

/1)1/(

Min, Motihashi, Lodder and Jansen, Nature Mat. 5, 817, 2006

ΔR

/RP

1)( 2 −∝L

lwindow sf

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

al)etAF(Mattana,examplethisinas

raszerotodrops

RR

b

sfnP

*

22

/1

/1)1/(

ττγγ

+−

=Δ

Condition


Condition for

spin injection

Nb rr /*

ΔR

/RP

1.6

1.2

0.8

0.4

0.0

L=20nmL

L10-4 10-2 100 102 104

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

10-4 10-2 100 102 1040.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

NlSF=2µm

tN=20nm

tN=2µm

tN=200nm

rb

*/rN

ΔR

/RP

Condition


Condition for

spin injection

Nb rr /*

F1 F2Semiconductor

channel

V

L

F1 F2Semiconductor

channel

V

L

ΔR

/RP

1.6

1.2

0.8

0.4

0.0

L=20nmL

L



b

g ( )

1E-3 0.01 0.10

10

20

30

40

50

T=4K

GaAs QW=6nm

1.95nm1.45nm1.7nm

MR

( %

)

b

g ( )

1E-3 0.01 0.10

10

20

30

40

50

T=4K

GaAs QW=6nm

1.95nm1.45nm1.7nm

MR

( %

)

)( 2* cmr b Ω

GaMnAs/AlAs/GaAs/AlAs/GaMnAs vertical structure

vrL

vt

L

timedwell

b

rn

*

*2

∝=τAF and Jaffrès

PR B 2001* +cond-mat 0612495, +

IEEE Tr.El.Dev*. 54,5,921,2007

*calculation. for Co and GaAs

at RT

NsflL / Ll N

sf /


1)( 2 −∝L

lwindow sf

La2/3 Sr1/3 MnO3 (LSMO)

La2/3 Sr1/3 MnO3 (LSMO)

Carbon nanotubes between spin-polarized sources and drains

MR=72 %

P

MR=60 %

L ≈

1-2 μm

MR=54 %

MR=45 %

Artist: Takis Kontos

drainsourcenanotube

VSD

Quasi-continuous DOS, same conditions as for semiconducting or metallic channel

(also diffusive transport regime)

Uc =e2/2CδE+Uc

eΔV ≈

meV

Usual conditions: experiments

at

small

bias voltage

LSMO/CNT/LSMO: experiments

at

higher

voltage, thanks

to relatively

large interface

resistances

and small V2/R heating

at

large V

Oscillatory variation of the conductance, different signs of the MR depending on the

bias voltage and from sample to sample

Uc

≈

0.2-0.3 meV, δE ≈

1 meV

drainsourcenanotube

eΔV = 25-500 meV >> Coulomb energy and level

spacing,

4 K< T <120 K

drainsourcenanotube

VSD

Quasi-continuous DOS, same conditions as for semiconducting or metallic channel

(also diffusive transport regime)

Uc =e2/2CδE+Uc

eΔV ≈

meV

Usual conditions: experiments

at

small

bias voltage

LSMO/CNT/LSMO: experiments

at

higher

voltage, thanks

to relatively

large interface

resistances

and small V2/R heating

at

large V

Uc

≈

0.2-0.3 meV, δE ≈

1 meV

drainsourcenanotube

eΔV = 25-500 meV >> Coulomb energy and level

spacing,

4 K< T <120 K

Sahoo et al, Nat.Phys.2005

Carbon nanotubes between spin-polarized sources and drains

MR=72 %

P

MR=60 %

MR=54 %

MR=45 %

Bias and temperature dependence of MR

MR=60%

MR/M

R(5K,25mV)

Nanotubes (also

graphene, other

molecules) :

Semiconductors:

sfnsfnP if

RRP

P

ττττγγ

<+

−=

Δ

===

largeis,/1

)1/(),off(Aand(on)Pbetweencontrastthe:

Sinjectionγlifetime,spinτtime,dwellτ:drainandsourceSPbetweenTransport22

sfn

*brresistanceinterfacefromderivedrtandCNTofvL,from60nsnτ:CNT* =

1.5 μm (MWCNT)

LSMO LSMO4109. −×= Otr

rb * ≅70 MΩ

*)60(2

)50ns5(long

nsshortrelativelybecanrtvL

nvvelocityhigh

issflifetimespinorbitspinsmall

=→

−≈→−

τ

τ

sfrtvL

nlongsmallerisvbut

cmelnforCNTinaslongasbecansf

ττ

τ

>>=→

−≈

2

)3/171610(

with τn ≈

60ns* (from interface resist.)

fit with τsf ≈

30ns (lsf =48μm) and γ

= 0.8

→ τn ≈ τsf (Hueso, AF et al,Nat.07)

Nanotubes

(also graphene, other molecules) :

Semiconductors:

sfnsfnP if

RRP

P

ττττγγ

<+

−=

Δ

===

largeis,/1

)1/(),off(Aand(on)Pbetweencontrastthe:

Sinjectionγlifetime,spinτtime,dwellτ:drainandsourceSPbetweenTransport22

sfn

*)60(2

)50ns5(long

nsshortrelativelybecanrtvL

nvvelocityhigh

issflifetimespinorbitspinsmall

=→

−≈→−

τ

τ

sfrtvL

nlongsmallerisvbut

cmelnforCNTinaslongasbecansf

ττ

τ

>>=→

−≈

2

)3/171610(

Solution for semiconductors:

shorter L ?, larger transmission tr ?

Improvement for nanotubes:

slightly larger

transmission tr

and longer spin lifetime with the

spin

polarization directed along the tube

- τn ≈

60ns*, τsf > 4 ns if γ

< 0.95

or τsf ≈

30ns (lsf =48μm) for γ

= 0.8

→ τn ≈ τsf (Hueso, AF et al,Nat.07)

Next challenge for nanotubes (or graphene…):

spin control by a gate potential

Nanotubes, graphene..

Molecules in general

Promising potential of molecular spintronics

New materials for spintronics (carbon nanotubes, graphene, molecules, ….)

Examples of new materials

GrapheneCarbon nanotubes

Molecules

MR of LSMO/Alq3/Co structures (preliminary results)

Collaboration CNRS/Thales [C. Barraud, P. Seneor et al) and CNR Bologna (Dediu et al)]

Alq3 (50nm)LSMO

Co

resist

1- 4 nmCo nanocontact

≈10 nm

LSMO Co

Alq3

LUMO

HOMOAlq3 = π

-

conjugated 8-hydroxy-quinoline aluminium

ELECTRONICS

SPINTRONICS

Summary¤Already important aplications of GMR/TMR (HDD, MRAM..) and now promising new fields

-Spin transfer for magnetic switching and microwave generation

-Spintronics with semiconductors, molecules or nanoparticles

M. Anane, C. Barraud, A. Barthélémy, H. Bea, A. Bernand- Mantel, M. Bibes, O. Boulle, K.Bouzehouane, O. Copi, V.Cros, C. Deranlot, B. Georges, J-M. George, J.Grollier, H. Jaffrès, S.

Laribi, J-L. Maurice, R. Mattana, F. Petroff, P. Seneor, M. Tran F. Van Dau, A. Vaurès

Université

Paris-Sud and Unité

Mixte

de Physique CNRS-Thales, Orsay, France

P.M. Levy, New York Un., A.Hamzic, M. Basletic Zagreb University

B. Lépine, A. Guivarch and G. JezequelUnité

PALMS, Université

de Rennes

, Rennes, France

G. Faini, R. Giraud, A. Lemaître: CNRS-LPN, Marcoussis, France

L. Hueso, N.Mathur, Cambridge

J. Barnas, M. Gimtra, I. Weymann,

Poznan

University

Acknowledgements to

Présent et futur de la spintronique LAAS, 17/12/ 08 TMR, etc … Spintronics. Spin ... Other...

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Transcript of Présent et futur de la spintronique LAAS, 17/12/ 08 TMR, etc … Spintronics. Spin ... Other...