Multiferroics for SpintronicsMultiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007 6 Centre National de la Recherche Scientifique Multiferroics

1Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique

Multiferroics for spintronics

Manuel Bibes2

H. Béa1, M. Gajek1, X.-H. Zhu1, S. Fusil1, G. Herranz1, M. Basletic1, B. Warot-Fonrose3, S. Petit4, P. Bencok6, K. Bouzehouane1,

C. Deranlot1, E. Jacquet1, A. Barthélémy1, J. Fontcuberta5 and A. Fert1

1 Unité Mixte de Physique CNRS / Thales, Orsay (FRANCE)2 Institut d’Electronique Fondamentale, CNRS, Université Paris-Sud, Orsay (FRANCE)3 CEMES, CNRS, Toulouse (FRANCE)4 Laboratoire Léon Brillouin, CEA, Saclay (FRANCE)5 ICMAB, CSIC, Campus de la UAB, Bellaterra (SPAIN)6 European Synchrotron Radiation Facility, Grenoble (FRANCE)

Brought to you by PITP (www.pitp.phas.ubc.ca)

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Ferroelectric

Ferroelastic

P

E

Sensors

FeRAM

Ferroics and multiferroics

M

H

Magnetic Data Storage

Spintronics

Switchable parameter : MExternal stimulus : H

Ferromagnetic materials

Partially filled d/f shells



Ferroelastic Ferromagnetic

P

E

Sensors

FeRAM


M

H


Spintronics

Switchable parameter : PExternal stimulus : E

Ferroelectric materials

Lack of inversion symmetry



Ferroelectric

Ferroelastic Ferromagnetic

P

E

Sensors

FeRAM


M

H


Spintronics

Switchable parameter : M, PExternal stimulus : H, E

Multiple-state memories

Multiferroic materials

From Spaldin and Fiebig, Science 309, 391 (2005)

M switching by EP switching by H

Lack of inversion symmetry

Partially filled d/f shells



Magnetically polarizableFerro(i)magnetic

Electrically polarizableFerro(i)electric Magnetoelectric

Insulating oxides : a classification

PZT

BaTiO3

SrTiO3

MgO

PbZrO3

ZnOTiO2

PbTiO3

LaFeO3

LaMnO3

NiO

NiFe2O4

CoFe2O4

EuO

CoCr2O4

La0.1Bi0.9MnO3

BiMnO3

BiCrO3

BiFeO3

Cr2O3

TbMnO3

Tb Mn2O5

YMnO3

PZT

BaTiO3

SrTiO3

MgO

PbZrO3

ZnOTiO2

PbTiO3

LaFeO3

LaMnO3

NiO

NiFe2O4

CoFe2O4

EuO

CoCr2O4

La0.1Bi0.9MnO3

BiMnO3

BiCrO3

BiFeO3

Cr2O3

TbMnO3

Tb Mn2O5

YMnO3

Derived from Eerenstein, Mathur and Scott, Nature 442, 759 (2006)



Multiferroics - examples of magnetoelectric coupling

Apply a magnetic field : change magnetic stateswitch polarization on/off

(Gd,Dy,Tb)MnO3 : spiral magnets

Spiral ordering breaks inversion symmetry(improper) ferroelectricity appears(but no finite magnetization)

CoCr2O4 : conical magnet

Conical ordering breaks inversion symmetry(improper) ferroelectricity appears(with a finite magnetization)

Flip polarization direction by a magnetic fieldYamasaki et al, PRL 96, 207204 (2006)

Kimura et al, PRB 71, 224425 (2005)



Magnetically polarizableFerro(i)magnetic

Electrically polarizableFerro(i)electric Magnetoelectric

Insulating oxides : a classification

PZT

BaTiO3

SrTiO3

MgO

PbZrO3

ZnOTiO2

PbTiO3

LaFeO3

LaMnO3

NiO

NiFe2O4

CoFe2O4

EuO

CoCr2O4

La0.1Bi0.9MnO3

BiMnO3

BiCrO3

BiFeO3

Cr2O3

TbMnO3

Tb Mn2O5

YMnO3

PZT

BaTiO3

SrTiO3

MgO

PbZrO3

ZnOTiO2

PbTiO3

LaFeO3

LaMnO3

NiO

NiFe2O4

CoFe2O4

EuO

CoCr2O4

La0.1Bi0.9MnO3

BiMnO3

BiCrO3

BiFeO3

Cr2O3

TbMnO3

Tb Mn2O5

YMnO3

Derived from Eerenstein, Mathur and Scott, Nature 442, 759 (2006)



BiFeO3

A room-temperature antiferromagnetic ferroelectric



Ederer et Spaldin, Phys. Rev. B, 71, 060401 (R) (2005)

Neaton et al. Phys. Rev. B, 71, 014113 (2005)

Rhombohedral Perovskite (R3c)a=3.96Å, α=89.4°

FerroelectricTC=1100KPS=6µC/cm² (1970 paper, bad crystal)J. R. Teague et al., Solid State Commun., 8, 1073 (1970)

PS=60µC/cm² (2007 paper, good crystal)D. Lebeugle, M. Viret et al, PRB in pressCondmat/0706.0404

G-type AntiferromagneticTN=640KCanted spins → weak FM MS=0.01µB/f.u.Incommensurate cycloidal modulation

P. Fisher et al., J. Phys. C,13, 1931 (1980)Popov et al. in Magnetoelectric Interaction Pheno-mena in Crystals (NATO Science Series, 2004) p. 277

BiFeO3 : bulk properties Brought to you by PITP (www.pitp.phas.ubc.ca)


tBFO=70nm : MS=150emu/cm3 (~1µB/fu) tBFO=400nm : Ms=5emu/cm3 (0.03µB/f.u.)

Claim of enhanced polarization and magnetization compared to bulk

tBFO=200nm : PS=55µC/cm²

Wang et al., Science, 299, 1719 (2003) : BFO//STO (001)

BiFeO3 : thin films properties Brought to you by PITP (www.pitp.phas.ubc.ca)


102

104

106

108

Inte

nsity

(cou

nts)

20 40 60 80 100

102

104

106

108

2θ (°)

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

S S S S

S S S S

10-4

6.10-3

10-1

520°C

580°C

750°C

P=1.2 10-2 mbar

Tdep=580°C

tBFO=70nm

tBFO=70nm

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

S S S S

S S S S

10-4

6.10-3

10-1

520°C

580°C

750°C

P=1.2 10-2 mbar

Tdep=580°C

tBFO=70nm

tBFO=70nm

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

S S S S

S S S S

10-4

6.10-3

10-1

520°C

580°C

750°C

P=1.2 10-2 mbar

Tdep=580°C

tBFO=70nm

tBFO=70nm

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

B

S S S S

S S S S

10-4

6.10-3

10-1

520°C

580°C

750°C

P=1.2 10-2 mbar

Tdep=580°C

tBFO=70nm

tBFO=70nm

B: BiFeO3, S: SrTiO3, *: γ-Fe2O3, : α-Fe2O3, :Bi2O3

Pulsed laser deposition on SrTiO3 (001)Target : Bi1.15FeO3

Growth conditions : T=580°C, PO2=6.10-3mbar

Bi much more volatile than Fe : • low P or high T (Bi evaporates more thanFe)⇒ Fe oxides• high P or low T (excess Bi)⇒Bi oxides

Growth of BiFeO3 thin films Brought to you by PITP (www.pitp.phas.ubc.ca)


1,0 1,1 1,2 1,3

10-4

10-3

10-2

10-1

P (m

bar)

1000 / Tdep (K-1)

1000 900 800

Presence of FeOx

Presence of BiOx

Tdep (K)

Pure BiFeO3

Pure BiFeO3 obtained in a verynarrow region around Tdep=580°C and PO2=6.10-3mbar

Appl. Phys. Lett.,87, 072508 (2005)

Growth of BiFeO3 thin films

Phase diagram



92 94 96 98 100 102

101

102

Inte

nsity

(cou

nts)

2θ (°)

120nmP=10-4mbar

92 93 94 95 96 97 98 99

20

40

60

80

100120

Inte

nsity

(cou

nts)

2θ (°)

25nmP=10-3mbar

B : BFOS : STOF : γ-Fe2O3

Quantification of γ-Fe2O3 by XRD : not easily detectable

20 40 60 80 100

102

103

104

105

106

107

108

PO2

=10-3mbar :

100nm

PO2

=10-4mbar :

120nm

25nm

60nm

Inte

nsity

(cou

nts)

2θ (°)

F ( 8

00)

F ( 4

00)B

(001

)S

(001

)

B (0

02)

B (0

03)

B (0

04)

S (0

02)

S (0

03)

S (0

04)

F ( 2

10)

F ( 4

20)

T=580°C

1,0 1,1 1,2 1,3

10-4

10-3

10-2

10-1

P (m

bar)

1000 / Tdep (K-1)

1000 900 800

Presence of FeOx

Presence of BiOx

Tdep (K)

Pure BiFeO3

Growth of BiFeO3 thin films – Parasitic Fe-rich phases

X-ray diffraction



Phys. Rev. B, 74, 020101R (2006)

Similar conclusions :Eerenstein et al. Science, 307 1203a (2005)Wang et al., Science, 307, 1203b (2005)

0 1 2 3 40

10

20

30

40

50

M (1

0-5 e

mu)

γ-Fe2O3 peak area (u.a.)

Magnetic moment comes from γ-Fe2O3

-6 -4 -2 0 2 4 6-150

-75

0

75

150

PO2=6 10-3mbar 120nm

PO2=10-4mbar 120nm

PO2=10-3mbar : 25nm 60nm 100nm

M (e

mu.

cm-3)

H (kOe)

Tdep=580°CSQUID, 10K

BFO + γ-Fe2O3 : up to Ms~150emu/cm3

γ-Fe2O3 ferrimagnetic (Ms=430emu/cm3)Pure BFO : Ms~2emu/cm3

BFO weak bulk-like ferromagneticmoment

Growth of BiFeO3 thin films – Parasitic Fe-rich phases

SQUID measurements



G-type antiferromagnetic order as in bulk BFO

No cycloidal modulationcontrary to bulk BFO

Linear magnetoelectric effectallowedPhil. Mag. Lett. 87, 165 (2007)(Special issue on multiferroic thin filmsEds. N.D. Mathur and MB)

In R3c bulk BFO : [003]*H single peak → G-type antiferromagnet[101]*H peak with satellites → cycloidal modulation⇒ Averaging to zero of the linear ME effect

In pseudo-cubic notation : [003]*H → [½ ½ ½]*C[101]*H → [-½ -½ ½]*C

from Sosnowska et al., J. Phys. C, 15, 4835 (1982)

BFO(240nm)//STO (001)

(a )

0.48 0.49 0.5 0 0.51 0.5 2

0

5 0

10 0

15 0

20 0

25 0

30 0 da ta f it

Inte

nsity

(arb

. uni

ts)

q h= q k=q l

[½ ½ ½ ]* k= 1.55Å -1

(a )

0.48 0.49 0.5 0 0.51 0.5 2

0

5 0

10 0

15 0

20 0

25 0

30 0 da ta f it

Inte

nsity

(arb

. uni

ts)

q h= q k=q l

[½ ½ ½ ]* k= 1.55Å -1

(c)

48 -0.52 -0.51 -0.50 -0.49 -0.48

0

50

100

150

data fit simulated

peaks (SP) sum of SP

qh=qk=-ql

Inte

nsity

(arb

. uni

ts)

[-½ -½ ½]* k=1.2Å-1

(c)

48 -0.52 -0.51 -0.50 -0.49 -0.48

0

50

100

150

data fit simulated

peaks (SP) sum of SP

qh=qk=-ql

Inte

nsity

(arb

. uni

ts)

[-½ -½ ½]* k=1.2Å-1

(001) BiFeO3 films – Magnetic properties

Neutron diffraction



(001) BiFeO3 films – Ferroelectric properties

-10 -8 -6 -4 -2 0 2 4 6 8 10

-100

-80

-60

-40

-20

0

20

40

60

80

100

Pol

ariz

atio

n (µ

C/c

m²)

Voltage (V)

Polarization loops

-6 -4 -2 0 2 4 6-30-25-20-15-10-505

101520

d33

(pm

/V)

Vdc(Volts)

Piezoelectric loops

BFO films are ferroelectric with a large polarization (~70 µC/cm²) and piezoelectricwith a d33 coefficient of ~20 pm/V

Ferroelectricity is preserved down to 2 nm.

60 nm 2 nm

Piezoresponse force microscopy

Jpn. J. of Appl. Phys., 45, L187 (2006)



Binek et Doudin, JPCM, 17, L39 (2005)

Electric field control of the junctionresistance state

Magnetic tunnel junction with multiferroicbarrier (FE and AFM)

Examples of devices

Bottom electrode

AF-FE

V

Principle : voltage-controlled exchange bias

Spin-valve on top of a multiferroicfilm (FE and AFM)

Prerequisites : 1. observe robust exchange bias at room-temperature2. spin-dependent tunneling through multiferroic barrier3. switch exchange bias direction by E-field (magnetoelectric coupling)



CoFeB deposited by sputteringHc=42Oe, He=-62OeAppl. Phys. Lett.,89, 242114 (2006)

-300 -200 -100 0 100 200 300

-50

0

50

M (µ

emu)

H (Oe)

-300 -200 -100 0 100 200 300

-50

0

50

M (µ

emu)

H (Oe)-300 -200 -100 0 100 200 300

-50

0

50

M (µ

emu)

H (Oe)

HmeasHdep

Hmeas

Hdep⊗

Hmeas

Hdep

AGFMT=300K

AGFMT=300K

AGFMT=300K

Robust room temperatureexchange bias between BFO andCoFeB

AuCoFeB 5nm BFO 35nm

0 1 2 3 4 5 6 7 8 9 10 11

With NiFe : J. Dho et al., Adv. Mat., 18, 1445 (2006)

0

10

2080

90

|Hc|

(Oe)

Cycle number

(e)( ) (Oe)( ) (Oe)

0 1 2 3 4 5 6 7 8 9 10 110

10

2080

90

|Hc|

(Oe)

Cycle number

(e)

0 1 2 3 4 5 6 7 8 9 10 110

10

2080

90

|Hc|

(Oe)

Cycle number0 1 2 3 4 5 6 7 8 9 10 11

0

10

2080

90

|Hc|

(Oe)

Cycle number

(e)( ) (Oe)( ) (Oe)

-300 -200 -100 0 100 200 300

-50

0

50

M (µ

emu)

H (Oe)

(a)

-300 -200 -100 0 100 200 300

-50

0

50

M (µ

emu)

H (Oe)

(a)CoFeB//SiO2

Exchange bias with BiFeO3 films Brought to you by PITP (www.pitp.phas.ubc.ca)


GMR measured on top of BFO at RTExchange bias has shifted the GMR curve

AuCoFeB

CuCoFeBBFO

-150 -100 -50 0 50 100 150

22,584

22,586

22,588

R (O

hm)

H (Oe)

300K

Exchange bias with BiFeO3 films Brought to you by PITP (www.pitp.phas.ubc.ca)


Positive TMR up to ~30%rather large value for an AFM barrierpositive spin polarization at Co/BFO interface

TMR vanishes around 200K : Local deoxygenation of LSMO

O2 growthpressure :6.10-3 mbar0.46 mbar

CoO 2.5nmCo 12.5nmBFO 5nm

LSMO 15nm

Tunnel junctions with BiFeO3 barriers

-3 -2 -1 0 1 2 3640

680

720

760

800

0

5

10

15

20

0 50 100 150 200 2500.0

0.2

0.4

0.6

0.8

1.0

1.2

R (k

Ohm

)

H (kOe)

TM

R (%

)TM

R /

TMR

3K (a

rb. u

nits

)

T (K)

3K10mV

T*

(a)

(b)-3 -2 -1 0 1 2 3

640

680

720

760

800

0

5

10

15

20

0 50 100 150 200 2500.0

0.2

0.4

0.6

0.8

1.0

1.2

R (k

Ohm

)

H (kOe)

TM

R (%

)TM

R /

TMR

3K (a

rb. u

nits

)

T (K)

3K10mV

T*T*

(a)

(b)

Appl. Phys. Lett., 89, 242114 (2006)

S~30x30µm²

(exchange bias due to CoO, not to BFO)



Positive TMR up to ~100%larger value than without STOpolarization at Co/BFO interface still positivethanks to STO, better quality of the upper LSMO

interface see Appl. Phys. Lett., 82, 233 (2003)

-2 -1 0 1 2

2,0

2,5

3,0

3,5

4,0

4,5

-20

0

20

40

60

80

100

R (M

Ohm

)

H (kOe)

S~50x50nm²10mV3K

TM

R (%

)

O2 growthpressure :6.10-3 mbar0.46 mbar0.46 mbar

CoO 2.5nmCo 12.5nmBFO 5nm

STO 1.6nmLSMO15nm

0 50 100 150 200 250 300

0

20

40

60

80

100

120

TMR

(%)

Temperature (K)

T*

Tunnel junctions with BiFeO3 barriers Brought to you by PITP (www.pitp.phas.ubc.ca)


-1000 -500 0 500 1000

6

8

10

12

14

16

TM

R (%

)

Bias (mV)

-2 -1 0 1 210

0

-10

-20

-30

-40

-50

TMR

(%)

VDC (V)

LAO

STO

Bias dependence of TMR in LSMO/STO/Co and LSMO/LAO/Co

junctionsScience 286, 507 (1999)APL 87, 212501 (2005)

Tunnel junctions with BiFeO3 barriers

TMR is positive and decreases symmetrically with bias voltageBehaviour is completely different from the case of LSMO/STO/Co and LSMO/LAO/Co junctionsPossible reasons : oxygen vacancies at LSMO/BFO interface, symmetry filtering, etc



Magnetoelectric switching

P along <111> directions :8 possible variants

Important to know and control the ferroelectric domain structure

Domain structure and magnetoelectric switching

When an electric field is applied, P can be switchedto different directionsOnly some of them yield a rotation of the AF plane

AF plane

Zhao et al, Nat. Materials (2006)



Domain structure

(001) films (111) films

OP

IP

OP

IP

8 variants are present

only 4 variants are present

(001) BiFeO3 films – Ferroelectric properties

(001) film 0.8° miscut

(001) film 4° miscut

IP IP

8 variants are present

only 4 variants are present

Piezoresponse force microscopy (PFM)

Domain structure can be controlled by playing with the substrate miscut angle and/or orientation.

Das et al., APL, 88, 242904 (2006)

Ideally, one type of domain orientation would be required, withthe appropriate polarization switching mechanism (109° ?)



(La,Bi)MnO3

A ferromagnetic ferroelectric



Ferromagnetic tunnel barriers

Ferromagnetic tunnel barriers: the spin-filter effect

exchϕΔ

Non Magn.Metal

Ferro.Insulator

0ϕ

Ferro.Half Metal

Parallel Config.

Antiparallel Config.

low I, large R

2/10 )

2( exch

eJϕϕ Δ

±−

↑↓ ∝

Since the tunnel transmission depends exponentially on the barrier

height, a highly-spin polarizedcurrent is generated by the barrier.

↓↑

↓↑

+−

=JJ

JJPB

BE

BE

PPPPTMR

−=

12

Expected TMR :

large I, low R



P. LeClair et al, APL 80, 625 (2002)

Au/EuS/Gd spin-filterFerromagnetic Gd is used as the spin-analyzer

Ferromagnetic tunnel barriers

Spin-filters

Au/EuS/Al spin-filterSuperconducting Al is used the spin-analyzer

J.S. Moodera et al, PRB 42, 8235 (1990)

Early spin-filtering experiments focused on Eu chalcogenides

Large spin-filtering efficiency (>90%) have been measured

Limited by low Tc of EuX compoundsFerromagnetic oxides



BiMnO3

a

b

c

xyz

Mn +3 d4

O -2

Bi +3

a

b

c

xyz

Mn +3 d4

O -2

Bi +3

Synthesis at high pressureDistorted perovskite structure(Monoclinic symmetry)Polar structureFerroelectric (?) Son et al, APL 84, 4971 (2004)« Magnetodielectric effect » observed in bulk

samplesKimura et al, PRB 67, 180401 (2003)

Crystal structure Magnetic ordering

Unusual orbital ordering resulting fromBi6s-O2p interaction Moreira dos Santos et al, PRB 66 064425 (2002)

Ferromagnetic orderTC=105K, Ms=3.6 µB

Ferromagnetic insulator withEg↑ = 0.5 eV and Eg↓ = 2.6 eV

Electronic structure

Shishidou et al, JPCM 2005

Partial substitution of Bi by La : lower synthesis pressure, stabilization of perovskite phase Troyanchuk et al, Low. Temp. Phys. 28, 569 (2002).Growth of BiMnO3 and La0.1Bi0.9MnO3 thin films



La1-xBixMnO3 thin films

BMO films have a reduced moment compared to bulkTC close to bulk (105K)Substitution by La further reduces max. moment and

slightly decreases TC (as in bulk)Low magnetic moment likely due to Bi vacanciesVery thin films are also ferromagnetic

Magnetic properties

-10 -8 -6 -4 -2 0 2 4 6 8 10

-300

-200

-100

0

100

200

300

M (e

mu/

cm3 )

H (kOe)

BMO x=0 ; 30nm LBMO x=0.1 ; 30nm

0 50 100 150 2000

20

40

60

80

100

120

140

160

180 BMO x=0 ; 30nm LBMO x=0.1 ; 30nm

M (e

mu.

cm-3)

T (K)

10K

-10 -5 0 5 10-300

-150

0

150

300

M (e

mu/

cm3 )

H(kOe)

LBMO7 nm

Growth by PLD

Single phase films only in a very narrow windowLa-substitution helps to stabilize the perovskite phase

PRB 75, 174417 (2007)

JAP 97 103909 (2005)

See for details :

KrF laser at 2 HzFluence: 2 J/cm².

O2 Pressure: 10-1 mbar.Tdep from 575°C to 700°C



Ferroelectric properties

-4 -2 0 2 4 6

-100

-50

0

50

100

-4 -2 0 2 4-2-1012

Pha

se (d

eg)

VDC (V)

VDC

(V)

d 33 (p

m.V

-1)

La0.1Bi0.9MnO3 thin films

Nature Materials 6, 196 (2007)

LBMO(30nm)/LSMO

PFM image afterwriting stripes at+/-4V

0°

180°

0°

180°

0°

180°

LBMO films as thin as 2 nm are still ferroelectric at room temperature

LBMO(2nm)/LSMO



BiMnO3-based junctions

Large TMR at low temperaturespin-filtering by the BMO layer

Polarization induced by BMO : 22%Spin-filter effect vanishes at T < TC

Thick resist

Thin resist

nanojunction

I(V)

Au

Thick resist

LSMO

Thin resist

nanojunction

I(V)I(V)

Au

STO (1nm)

BMO (4nm)

Thick resist

Thin resist

nanojunction

I(V)I(V)

Au

Thick resist

LSMO

Thin resist

nanojunction

I(V)I(V)

Au

STO (1nm)

Tunnel magnetoresistance

-6 -4 -2 0 2 4 6

0.4

0.6

0.8

11.21.4

10

15

20

-0.4 0.0 0.4

-50

0

50

R (M

Ω)

H (kOe)

R (M

Ω)

I (n

A)

VDC

(V)

TMR

~ 5

0%

3K

8K

20K30K

60K

LSMOBMO

Junction #1

Junction #2

VDC=10mV, T=3K

PRB 72 020406(R) (2005)

LSMO / STO (1 nm) / BMO (4 nm) / Au

Nanoletters 3, 1599 (2003)

Junctions defined by nano-indentation lithography



LBMO-based junctions

Tunnel magnetoresistance

-6 -4 -2 0 2 4

50

100

150

200

H (kOe)

R (M

Ω)

-0.5 0.0 0.5-0.2-0.10.00.10.2

I (µA

)

VDC (V)

10 mV

20 mV

50 mV

TMR

= 9

0%

Polarization induced by LBMO : 35%TMR decreases rapidly with bias

Magnons ? Defects ?

4K

JAP 99, 08E504 (2006)

LSMO / STO (1 nm) / LBMO (4 nm) / Au




T=4K

-3 -2 -1 0 1 2 3

-40

-20

0

20

40

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.60.0

0.5

1.0

1.5

2.0

E (MV.cm-1)

I (µA

)G

(10-4

Ω-1)

VDC (V)

(a)

(b)

0.0 0.5 1.0 1.5 2.00

200

400

600

I (µA

)

VDC (V)

T=4K

-3 -2 -1 0 1 2 3

-40

-20

0

20

40

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.60.0

0.5

1.0

1.5

2.0

E (MV.cm-1)

I (µA

)G

(10-4

Ω-1)

VDC (V)

(a)

(b)

0.0 0.5 1.0 1.5 2.00

200

400

600

I (µA

)

VDC (V)

Tunnel electroresistance

A ~20% electroresistance effect is observedThe shape of the G(V) curve suggests direct

tunneling

LSMO / LBMO (2 nm) / Au

-2 -1 0 1 20

5

10

15

20

25

What is the origin of the TER ?

TER

(%)

VDC (V)




Ferroelectric tunnel barriers

From Tsymbal and KohlstedtScience 313, 181 (2006)

Tunneling through a ferroelectric tunnel barrier

Several mechanisms leading to currentmodulation upon polarization reversal





















EF

LSMO Au

Φ0

P

LSMO Au

Φ-



P

EF

LSMO Au

Φ+

Large average barrier heightlow tunnel current

Low average barrier heightlarge tunnel current

Hysteretic I(V) curves are expectedAn electroresistance effect should occur upon polarization reversal

See details in Zhuravlev et al, PRL 94, 246802 (2005)



-4 -2 0 2 4

100

120

140

160

180

After -2V

After +2V

R (k

Ω)

H (kOe)

10mV 3K

-3 0 324

28

32

36

40

-3 0 3 -3 0 3 -3 0 324

28

32

36

40

R(k

Ω)

H (kOe) H (kOe)

H (kOe)

R (k

Ω)

H (kOe)

After –1.5V After +1.5V After –1.5V After +1.5V


Combination of tunnel electroresistance and magnetoresistance

Demonstration of a 4-resistance state system with a multiferroic barrierEffect was observed on several junctions and is reproducible

1

2

LSMOLBMO

Au

3

4

4

3

2

1




Temperature dependence of TER and TMR consistent with an originrelated to to ferroelectricity and ferromagnetism, respectively


10 1000

20406080

100

0

5

10

15

20

TMR

(%)

T (K)

TER

(%)

TCM

Bulk BMOTCE

Temperature dependence of TER and TMR



Conclusions and perspectives

BiFeO3Single phase films can be grown in a narrow range of P and TThey are G-type antiferromagnetic and ferroelectric at RTLSMO/BFO/Co junctions show a large positive TMRBFO induced exchange bias on CoFeB

(La,Bi)MnO3 based junctionsLa0.1Bi0.9MnO3 films are ferromagnetic and ferroelectricLBMO junctions show TMR and electroresistance (4 resistance states)We suggest electroresistance effect due to ferroelectric switching in the barrierControl of the magnetic state by electric field ?

Perspectives :Magnetization manipulation with an electric field at RTNew materials, ideally ferromagnetic multiferroics with high TCs, MSand P are required

Financial support by EU Streps Nanotemplates and MaCoMuFi, EU Marie-Curie program, ESF Thiox program, French ANR program, Spanish Ministry for Research and EGIDE

See review on Oxide Spintronics by M. Bibes and A. Barthélémy, IEEE Trans. Electron Devices 54, 1003 (2007)


Documents

Multiferroics for SpintronicsMultiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007 6 Centre National de la Recherche Scientifique Multiferroics