Multiferroics for SpintronicsMultiferroics for spintronics Manuel Bibes Quantum Nanoscience with...
Transcript of Multiferroics for SpintronicsMultiferroics for spintronics Manuel Bibes Quantum Nanoscience with...
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)
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2Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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3Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
Ferroelastic Ferromagnetic
P
E
Sensors
FeRAM
Ferroics and multiferroics
M
H
Magnetic Data Storage
Spintronics
Switchable parameter : PExternal stimulus : E
Ferroelectric materials
Lack of inversion symmetry
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4Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
Ferroelectric
Ferroelastic Ferromagnetic
P
E
Sensors
FeRAM
Ferroics and multiferroics
M
H
Magnetic Data Storage
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
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5Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
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6Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
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7Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
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8Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
BiFeO3
A room-temperature antiferromagnetic ferroelectric
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9Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
10Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
11Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
12Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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13Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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14Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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15Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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16Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
(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)
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17Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
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18Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
19Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
20Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
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21Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
22Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
-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
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23Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
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24Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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° ?)
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25Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
(La,Bi)MnO3
A ferromagnetic ferroelectric
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26Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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27Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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28Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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29Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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30Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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31Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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32Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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
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33Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
LBMO-based junctions
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)
Nature Materials 6, 196 (2007)
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34Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
Ferroelectric tunnel barriers
From Tsymbal and KohlstedtScience 313, 181 (2006)
Tunneling through a ferroelectric tunnel barrier
Several mechanisms leading to currentmodulation upon polarization reversal
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35Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
Ferroelectric tunnel barriers
Tunneling through a ferroelectric tunnel barrier
From Tsymbal and KohlstedtScience 313, 181 (2006)
Several mechanisms leading to currentmodulation upon polarization reversal
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36Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
Ferroelectric tunnel barriers
Tunneling through a ferroelectric tunnel barrier
From Tsymbal and KohlstedtScience 313, 181 (2006)
Several mechanisms leading to currentmodulation upon polarization reversal
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37Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
Ferroelectric tunnel barriers
Tunneling through a ferroelectric tunnel barrier
From Tsymbal and KohlstedtScience 313, 181 (2006)
Several mechanisms leading to currentmodulation upon polarization reversal
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38Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
EF
LSMO Au
Φ0
P
LSMO Au
Φ-
Ferroelectric tunnel barriers
Tunneling through a ferroelectric tunnel barrier
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)
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39Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
-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
LBMO-based junctions
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
Nature Materials 6, 196 (2007)
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40Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
Temperature dependence of TER and TMR consistent with an originrelated to to ferroelectricity and ferromagnetism, respectively
LBMO-based junctions
10 1000
20406080
100
0
5
10
15
20
TMR
(%)
T (K)
TER
(%)
TCM
Bulk BMOTCE
Temperature dependence of TER and TMR
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41Multiferroics for spintronics Manuel Bibes Quantum Nanoscience with Spins, Asilomar 3-6 June, 2007Centre National de la Recherche Scientifique
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)
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