Ldb Convergenze Parallele_08

D. Komskii, Physics 2, 20 (2009)

Multiferroic materials: overview and

some perspectives

J. Fontcuberta

Institut de Ciència de Materials de Barcelona, CSIC

Bellaterra, Catalunya, Spain

• Multiple (4) memories and logics

• Electric control of magnetic states (if coupling exists) • Novel optical components • …..

1

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acknowledgments

2

Barcelona

MAT2011-29269-C03-01, CONSOLIDER CSD2007- 00041

2009SGR-376, 2009SGR-203

http://www.icmab.es/imago/images/rsgallery/original/MR6V5588.JPG

../../../../../gherranz/Escritorio/logos_archivos/icmab5003.jpg

acknowledgments Institute of Physics, Polish Acad.of Sci., Warszawa

M. Wojcik and E. Jedryka (NMR)

Dept. Electrònica. U. Barcelona, Barcelona

S. Estradé and F. Peiró (TEM-EELS)

Lab. Phys. des Solides, UMR-CNRS Orsay, France

F. de la Peña, M. Walls, C. Colliex (S(TEM)-EELS)

ETH Zürich

Claude Ederer (DFT Theory)

Department of Physics, Univ. of Houston, USA

M. Iliev (Raman)

ALBA Synchrotron Light Source, Catalonia, Spain.

A. Barla, E. Pellegrin (XPS, LD)

Laboratorio TASC (Ts ), Italy

F. Bondino, E. Magnano (XPS, LD)

LNESS – Dipartimento di Fisica – Politecnico di Milano, Italy

R. Bertacco (multiferroics)

Consiglio Nazionale delle Ricerche, CNR-SPIN,L’Aquila, Italy

S. Picozzi (DFT Theory, multiferroics)

Laboratoire Structures, Propriétés et Modélisation des Solides,

Ecole Centrale Paris, (France)

B. Dkhil (hight temp XRD)

Institut de Ciència de Materials de

Barcelona, Catalonia, Spain

D. Pesquera

D. Gutierrez

N. Dix

J. M. Rebled

O. Vlasin

Monica Bernal

Mateusz Ścigaj

B. Casals

G. Radaelli (from P. Milano)

I. Fina (now at Halle, Germany)

X. Marti (now at Univ.. Berkeley)

L. Fàbrega

V. Laukin

V. Skumryev

F. Sánchez (PLD)

G. Herranz (MOKE)

3


Current research activities • Electronic/structural surface reconstructions in oxides

• Surface orbital filling at La1-xSrxMnO3 & related oxides • 2DEG at interfaces between band-gap insulators

• New Multiferroic materials and devices •Electric and magnetic control of M and P

Magnetic multiferroics (YMnO3, etc) Exchange biased multiferroics Multiferroic bilayers (BTO-CFO) Active multiferroic interfaces

•Double perovskites Bi2MM’O6

• Multifunctional heterostructures on Silicon • Ferroelectrics (Si//BaTiO3) • Magnetics (Si//CoFe2O4) • Hybrid (Si//BaTiO3/CoFe2O4)

• Magnetophotonic materials •Magnetic opals with enhanced Magnetooptic activity

4









D. Pesquera et al

Nature Comm. (2012)

5









G. Herranz et al

Scientific Rept. (Nature) (2012)

6



•Surface orbital filling at La1-xSrxMnO3 & related oxides • 2DEG at interfaces between band-gap insulators




• Multifunctional heterostructures on Silicon • Ferroelectrics (Si//BaTiO3) • Magnetics (Si//CoFe2O4) • Hybrid (Si//BaTiO3/CoFe2O4


7




• New Multiferroic materials •Electric and magnetic control of M and P





E. Langenberg et al. Phys. Rev. B (2012)

Bi2NiMnO6

8









M. Scigaj, et al, Appl. Phys. Lett. (2013) 9









M. Scigaj, et al, Appl. Phys. Lett in press

10



• Self-ordered chemical terminations at ABO3 surfaces • Surface orbital filling at La1-xSrxMnO3 & related oxides • 2DEG at interfaces between band-gap insulators

• New Multiferroic materials •Electric and magnetic control of M and P

Magnetic multiferroics (YMnO3, etc) Exchange biased multiferroics Multiferroic bilayers (BTO-CFO)



• Magnetooptic Laboratory •Recording magneto-electric images of magnetic and ferroeelectric domains dynamically

Ondrei . Vlasin in progress

11


12

2000. Why magnetic ferroelectric are so-scarce ?

N. Spalding

2003. Enhanced Polarization of BiFeO3 films

Ramesh group.

2003. A new class of Multiferroics: Magnetism drives ferroelectricity.

Kimura (TbMnO3)

Towards dreamed applications:

2006: E-controlled GMR:Exchange biased Ferromagnetic- Multiferroic

V. Laukhin et al (YMnO3/Py)

2007: Multiferroic M-Fe-RAMs:4-state memories

M. Gajeck et al (BiMnO3)

2009: Electric control of spin-polarization: Interface bonding

V. García (BaTiO3/Fe)

The renaissance of multiferroics

13

Objectives

Overview the main families of multiferroic materials and the relations between ferroelectric and magnetic orders and their coupling

Some hints for new approaches

Illustrate some potential applications

14

Index

Structural trends

Requirements for occurrence of magnetism and ferroelectricity.

The different families of multiferroics.

Potential applications: Electric and magnetic control of M and P

Summary

15

Index

Structural trends




Summary

16

Structural trends

ABO3

A

17

Structural trends : AMnO3

Hexagonal Orthorhombic

18

Index

Structural trends




Summary

19

Magnetism & ferroelectricity

Magnetism: partially filled 3dn states (dx- rule)

Insulating: to sustain polar states

Magnetic order: time reversal symmetry is broken

• Superexchange magnetic interactions: i.e Mn3+-O-Mn3+ : 3d4-2p6-3d4

• Goodenough-Kanamori rules: orbital filling and bond angles

Ferroelectricity: build-in electric dipoles. i.e center of positive and negative charges do not coincide (lack of inversion symmetry)

3d5: Fe3+ : Fe2O3 (AF); BiFeO3 , GdFeO3 (AF)

3d4: Mn3+ : Mn2O3 (AF); LaMnO3 (AF)

BiMnO3 (FM !!)

Structural trends




Summary

20

Index

21

Multiferroic Families

Type-I Multiferroics

Magnetism and Ferroelectricity have independent sources

Typically TCFE >> TN and weak coupling between P and M

P is often large (10-100 mC/cm2)

Type-II Multiferroics

Magnetic order causes ferroelectricity TC

FE < TN,C and strong coupling between P and M

P is much smaller (~0.01 mC/cm2)

Type-III Multiferroics

Domain walls and magnetic excitations Confined response TC

FE ≈ TN,C

Type-IV Multiferroics

Bilayers and Composites of known FE and FM (Magneto/ferro)elastic coupling @ RT

22

Type-I Multiferroics

1. Off-centering of 3d0 ions, i.e. BaTiO3

2. Stereochemical activity of lone-pairs of the large A-

ions in ABO3 creating dipoles, while moment

resides at B sites, i.e. BiMnO3 or BiFeO3

3. Geometrically driven ferroelectric, i.e. h-YMnO3

4. Charge ordering: B-O=B’-O-B-O=B´. Dipoles are

formed

23

Magneto-Electric coupling

Linear Magnetoelectrics (Cr2O3)

P

H

P M/Ms

TE TC/TN

“Type I” multiferroics (h-YMnO3)

weak ME coupling

P Ms

TN=TE

“Type II” multiferroics (TbMnO3)

can have strong ME coupling

Adapted from Radaelli

24

Type-II Multiferroics

1. Ferroelectricity arising from spiral magnetic order.

2. Ferroelectricity in collinear magnetic structures.

3. Electronic ferroelectrics: spin-dependent M-O hybridization.

• Symmetric exchange in collinear AF: P ~ J Si ·Sj HoMnO3

• Antisymmetric exchange in cycloidal AF: P ~ A rij × (Si × Si) TbMnO3

• Spin-dependent p-d hybridization in AF: P ~ A (Si·rij )2rij Ba2CoGe2O7

P P

P

p d

25

Couple magnetic moments to ion displacements

J (r)

k M M’

Direct exchange

J (q)

M k M’

Symmetric superexchange

SO coupling (anti-symmetric

superexchange)


26

Exchange, striction and polarization

Collinear magnetic ferroelectrics

Superexchange striction

27

Spin-orbit coupling: anti-symmetric superexchange

S.-W. Cheong & M. Mostovoy, Nature Mater. 6 13 (2007)

H. Katsura et al., PRL 95, 067205 (2005)

P J1

J2

1 2ijr S S p

Vector Coupling – Requires non-

collinearity

i.e. cicloidal antiferromagnets


Magnetic interactions in AMnO3 perovskites

The size of the lanthanide ion occupying the centre of the cage

determines the Octahedra rotations and thus the Mn-O-Mn bonding

angles

28

Magnetic interactions in AMnO3 perovskites

A-type E-type

Collinear magnetic order

Non-Ferroelectric

Collinear magnetic order

Ferroelectric

a-a

xis

Ho Er Tm Yb Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy

Bonding angle

a-axis

b-axis

b-axis

c-ax

is

P

Cycloidal & FE

M. Kenzelmann et al.,

PRL 95, 087206 (2005)

29

30

Type-II Multiferroics: magnetic ferrroelectrics

Y. Tokura et al. Adv. Mater. 2010

E-type : HoMnO3

bc-cycloids : DyMnO3

Symmetric exchange

Pa ~ Si· Sj

Antisymmetric exchange

P ~ eij x (Six Sj)

Pc: bc- cycloids

Pa: ab- cycloids

31

Type-III Multiferroics

Multiferroic domain walls

Bloch walls

Néel walls Similar to cycloid

32

Type-III Multiferroics: Multiferroic domain walls

A. S. Logginov et al, APL (2008)

33

1. Laminar nanocomposites

2. Columnar nanocomposites

Type-IV Multiferroics: Composites FE & FM

(from X. Zheng et al, Science 303, 661 (2004))

34

Growth of columnar FE & FM nanocomposites FE

• Unmiscible structures (spinel (FM) and perovskite (FE) ) • High anisotropy of surface energy: ( 001) vs (111)

(111)(001) Spinel

Perovskite

Column Matrix

ColumnMatrix

Zheng et.al, Nano Lett, 6, 1401 (2006)

(111)(001) Spinel

Perovskite

Column Matrix

ColumnMatrix

Zheng et.al, Nano Lett, 6, 1401 (2006)

R. Muralidharan, et al, JAP (2008)

CFO

BFO BFO

STO

100nm

CFO CFO

BFO

35

Magnetoelectric coupling in columnar nanocomposites

CoFe2O4/BiFeO3

SrTiO3 (001) 200nm 0 100 200 300 400

0

50

100

150

200

250

mag p

ha

se

(arb

. u

nits

)

X (nm)

SrTiO3 (001) 200nm

MFM, after poling -12V

MFM

0 100 200 300 400

0

50

100

150

200

250

ma

g p

ha

se

(arb

. u

nits

)

X (nm)

E-field control of the CoFe2O4

nanopillars magnetization

Work in collaboration with Univ.

Barcelona (M. Varela) & Univ. Geneve

Dix et al., Chem. Mater. 2009

Dix et al., APL 2009

Dix et al. ACS Nano 2010

Ferroelectric

BiFeO3 matrix

Ferromagnetic

CoFe2O4 pillars

Substrate

36

Index

Structural trends





Summary

Magnetic switching of polarization in thin films

Magnetic field

P YMnO3

Demonstration of switchable Polarization in multiferroic thin films

X. Martí et al. Appl Phys. Lett. 2009

X. Martí et al. Appl Phys. Lett. 2010

I. Fina et al App Phys Lett. 2010

I. Fina et al, Phys Rev. Lett (2011)

100 nm

P

•YMnO3 : bc-cycloidal

37

SrTiO3(001)

YMnO3(001) a

c

b

AF axis → b

a

Nb:STO(001) substrates

c-textured

Two (a,b) domains in-plane

Nb:STO(110) substrates

a-textured

One single (a,c) domain in-plane

X. Marti et al., Thin Solid Films 516, 4899 (2008)

SrTiO3(110)

YMnO3(100) c

a

b AF axis →

YMnO3 thin films

38

Ferroelectric properties of “relaxed” YMnO3 films

Two samples: a-textured and c-textured

Around 100 nm

Pt Pt

Pa Pc

39

Ferroelectric properties of YMnO3 films

-200 -100 0 100 200-75

-50

-25

0

25

50

75

0T

4.5 T

9T

I (m

A)

E (kV/cm)

increasing H

-200 -100 0 100 200

-30

-15

0

15

30

E (kV/cm)

I (m

A)

-90

-45

0

45

90

Pc (n

C/c

m2)

T = 5K

Polarization along c-axis (H=0) (Pc ≈ 90 nC/cm2)

Polarization along a-axis (H= 0 T) Pa ≈ 0

-150 -75 0 75 150

-6

-3

0

3

6 Pa (n

C/c

m2)

E (kV/cm)

I PU

ND (mA

)

-80

-40

0

40

80

-150 -75 0 75 150

-6

-3

0

3

6

I PU

ND (mA

)

Pa (n

C/c

m2)

-80

-40

0

40

80

E (kV/cm)

(H= 6 T) Pa ≈ 90 nC/cm2

40

I.Fina et al., APL 97, 232905(2010)

Cycloidal magnetic order and FE in YMnO3 films

H = 0

I.Fina et al., APL 97, 232905(2010)

I. Fina et al, Phys Rev. Lett 106, 057206 (2011)

c - axis

b - axis

a - axis

P//c-axis

H ≠ 0

P//a-axis

c - axis

b - axis

a - axis

Increasing H//c

41

42

b

c

a

Suppose an spiral structure with cycloid within the bc plane:

Pc

Pa

Magnetic field switching of P: from Pc to Pa

Coherent flopping and memory

T. Kimura et al , Nature 426, 55 (2003)

+c

DW ±a

DW-a/-c

c-axis

a-axisb-axis

-a-a

-c

+a +c

????!

Why polarization emerges along the direction of the initial poling ?

43

1 2

4

•100 % Polarization recovered •Full memory of initial state

3


44

1 2

3

No memory of the initial state ?

4

•Domain Walls: DWa+c+ and DWa+c- are to be formed. •The energy of domains walls become relevant •Pinning-Hysteresis ?


45

Equal chiral population : P+a = P-a ; Q +c = Q -c

An

tiferrom

agnetic

Paraelectric

bc-cycloidal

Paramagn

etic

(i)(ii)

(iii)

0 5 10 15 20 25 30 35 40 45-1

0

1

2

3

4

5

6

7

Hf (

T)

T (K)

?

?

(ii)

(iii)a-axis

c-axis

b-axis

0 100 200 3000

20

40

60

E (kV/cm)

1/2

I sw (

nA

)-300 -200 -100 0

-60

-40

-20

0

E (kV/cm)

1/2

I sw (

nA

)

m0H = 6 TP-a Pa

m0H = 6 TP+a Pa

Polarization flopping in YMnO3 thin films

Fina et al. PRL 107, 257601 (2011)

46

m0H = 6 T

E+ = 285kV/cm ?

? a-axis

c-axis

b-axis

H


oherent flopping and memory

47

m0H = 6 T

E+ = 285kV/cm ?

? a-axis

c-axis

b-axis

H

-300 -200 -100 0

-60

-40

-20

0

2/3

I sw (

nA

)

E (kV/cm)

m0H = 6 T

ND- 2/3

• After E-poling and successive flops of P the chiral state is preserved (P+a) !!!

• E-poling favours ONE chiral state that is memorized by the system

I. Fina et al. Phys. Rev. Lett. 107, 257601 (2011)


48

m0H = 6 T

E+ = 285kV/cm ?

? a-axis

c-axis

b-axis

H

m0H = 6 T

PU+ 1/3

0 100 200 3000

20

40

60

1/3

I sw (

nA

)

E (kV/cm) DW

I. Fina et al. Phys. Rev. Lett. 107, 257601 (2011)


Memory but only a partial P recovery

49

(Y1-xSmx)MnO3 crystals: background

Goto et al, Phys. Rev. B 92, 257201 (2004)

█ AFM █ FE

YTb

Daniel Thomas O’Flynn; PhD Thesis Univ. Warwick 2011 Supervisor: Prof. G. Balakrishnan

50

Polarization flopping in (Y1-xSmx)MnO3 crystals

D. T. O’Flynn et al, Phys. Rev. B 83, 174426 (2011)

paraelectric

ferroelectric ferroelectric

51

Magnetic field dependent polarization

I. Fina et al, submitted

0 2 4 6 8 100

10

20

30

40

50

T (

K)

m0H (T)

Sinusoidal AFM

Paramagnetic//Paraelectric

c

bP

bc-cycloid

Pb

a ab-cycloid

P//c

P//a

1 (E-poling)

2

3

4

5

6

0 3 6 9

0

300

600

Pa

+ (mC

/m2)

m0H (T)

0 10 20 30 40 50 60

0

300

600

Pa

+ (mC

/m2)

Temperature (K)

seed

DWDW DW

A P

P

B

C

DW

2

3

H//c

H=0

H//c

P

P ≈ 0

seed

(a)

1

6

2

34

5

(b)

(c)

A

B

C

(d)

A

C

m0H//c-axis = 9 T

T= 5 K

0 1 2

0

300

600

P(9

T)

(mC

/m2)

no of loops

A

52


I. Fina et al, in preparation

0 2 4 6 8 100

10

20

30

40

50

T (

K)

m0H (T)

Sinusoidal AFM

Paramagnetic//Paraelectric

c

bP

bc-cycloid

Pb

a ab-cycloid

P//c

P//a

1 (E-poling)

2

3

4

5

6

0 3 6 9

0

300

600

Pa

+ (mC

/m2)

m0H (T)

0 10 20 30 40 50 60

0

300

600

Pa

+ (mC

/m2)

Temperature (K)

seed

DWDW DW

A P

P

B

C

DW

2

3

H//c

H=0

H//c

P

P ≈ 0

seed

(a)

1

6

2

34

5

(b)

(c)

A

B

C

(d)

A

C

m0H//c-axis = 9 T

T= 5 K

0 1 2

0

300

600

P(9

T)

(mC

/m2)

no of loops seed

DW± DW ±

A PT

PT

B

C

DW ±

DWac DWacH-Flop

H-Flop

53


H-cycling

54

Phase coexistence within the collinear region

0 10 20 30 40 50 60

0

200

400

PR (

5K

, T

R)

(mC

/m2)

TR (K)

1,0

1,1

1,2

1,3

1,4

1,5

1,6

a /

a (50K

)

(a) (b) TNTcy

(c)

(i) (ii) (iii)

P ≈ 0

(i)

T = 5K TR < Tcy

Pa+ (ii)

T = 5K TR > Tcy

seed

(iii)

T = 5K TR < TN

P = PS

P = PS

P = PS

P = PS

P < PS

P = PS

P = 0

P = 0

0 10 20 30 40 50 60

0

200

400 30 K

35 K

40 K

50 K

60 K

17.5 K

20 K

22.5 K

25 K

27.5 K

Pa

+ (mC

/m2)

Temperature (K)

TNTcy

T-cy

clin

g

55

Conclusion

In YSmMnO3 cycloidal ferroelectric, Magnetic field can be used not only to flop P but also to modulate its value.

ab- and bc-regions embedded in the bc- or ab- cycloidal matrix are instrumental to keep memory of the polar history of the sample.

By T-cycling, polar seeds remain in the spin-collinear region and determine the polarization upon cooling.

Polar seeds can exists in paramagnetic state ? Search in frustrated magnetic systems.

56

57

Index

Structural trends





Summary

58

Electric switching of Magnetization:

exploiting exchange bias

M

Electric field

Ferroelectric & Antiferromagnetic

Soft Ferromagnet

M

Results on exploiting exchange bias to switch the magnetization using multiferroics

V. Lauhkin et al. Phys Rev Lett. (2006)

V. Skumryev et al Phys Rev Lett (2011)

59

Exchange biasing using multiferroics

V. Laukhin et al PRL 97, 227201 (2006)

Substrate STO(111)

Electrode: Pt

AF and FE h-YMnO3

Ferromagnet: Permalloy

AF/FE

FM

AF/FE

FM

V

(FE & AF) exchange coupled to a FM

60


V. Skumryev. J. Fontcuberta et al, Phys Rev Lett 2011

61


J. Fontcuberta et al, Phys Rev Lett 2011

62

Conclusion

Hexagonal manganites: a toy for E-induced M switching but only for low Temperature

Not reversible: H should be applied to re-initiate (write)

63

Index

Structural trends





Summary

64

Index

Structural trends





Summary

65

Multiferroic Tunnel Junctions

P P

EF

LSMO Au LSMO Au

0 0+ -

LSMO

EF

Au

0

ex

Parallel Antiparallel

LSMO

EF

Au

MLSMO MLBMOMLSMO MLBMO

P P

EF

LSMO Au LSMO Au

0 0+ -

LSMO

EF

Au

0

ex

LSMO

EF

Au

0

ex

Parallel Antiparallel

LSMO

EF

AuLSMO

EF

Au

MLSMO MLBMOMLSMO MLBMO

Au BiMnO3

LSMO

M. Gajek et al Nature Materials 6, 256 (2007)

66

Multiferroic Memories

V. Garcia et al, Science 327, 1106 (2010)

E. Y. Tsimbal et al, PRL 97, 047201 (2006)

67

ON/OFF switching of magnetization

G. Radaelli et al, submitted et al,

68



69


G. Radeelli et al, submitted et al,

70



DFT calculations by S. Piicozzi et al

71

Conclusion

Magnetization of interface in BaTiO3/Fe can be switched ON/OFF by an electric field.

Huge interface magnetoelectric coupling.

Room temperature applications

Many new possibilities

72

• The race towards novel multiferroics has lead to a new and deep understanding of magnetoelectric coupling in oxides.

• The recognition that magnetic frustration, eventually enhanced exploiting epitaxial strains, could be of relevance for the discovery of new MF materials and opens a door for further research.

• Multiferroic response of domain walls and magnetic excitations is just starting.

• Interface coupling among multiferroic materials or even distinct ferroic orders may lead to breakthrough results and novel applications

Summary

Financed by:

Spanish MEC (NAN2004, Mat2008 and Consolider-Nanoselect ),

Generalitat de Catalunya, UE Proj. MaCoMuFi

ConsoliderConsolider

73

grazie gracies

74

75

Index

Structural trends





Summary

76

Direct ME effect in multiferroic bilayers (BaTiO3-

CoFe2O4)

2-2 nanostructure 2-2 Multilayer

Bottom BTO Top BTO

= Low BaTiO3 response = High BaTiO3 response

K

k

k

K

Pt PtPt Pt

Samples Bottom BTO Top BTO

77

-1000 -500 0 500 1000

-75

-50

-25

0

25

50

75 Bottom BaTiO

3

Top BaTiO3

P (mC

/cm

2)

E (kV/cm)

bulk

0 100 200 300 400

15

20

25

30

35

r

Temperature (K)0 100 200 300 400

20

40

60

80

r

Temperature (K)

-1000 -500 0 500 1000

-1.0

-0.5

0.0

0.5

1.0

Bottom BaTiO3

Top BaTiO3

I (A

/cm

2)

E (kV/cm)

x10

T1

T2

T1

T2

Multiferroic characterization

-8 -6 -4 -2 0 2 4 6-400

-300

-200

-100

0

100

200

300

400

M (

em

u/c

m3)

m0H (T)

in-plane

out-of-plane

-8 -6 -4 -2 0 2 4 6-400

-300

-200

-100

0

100

200

300

400

in-plane

out-of-plane

M (

emu/

cm3)

m0H (T)

78

Magnetodielectric characterization

0 100 200 300 400

15

20

25

30

35

0T

9T

r

Temperature (K)

T1

T2

0 100 200 300 400

10

100

0T

9T

r

Temperature (K)

T1

T2

0 100 200 300 400

0

10

20

30

40

170 180 1900.0

0.1

0.2

(%)

Temperature (K)

T2 ’ T1 ’ T3 ’

T O

R

C

0 100 200 300 4000,0

0,5

1,0

1,5

2,0

2,5

(%)

Temperature (K)

T O R

T2 ’ T1 ’ T3’

C

79

Conclusions

Bottom BTO: FE clamped to the

substrate

Top BTO: FE clamped to

the FM

= Low BaTiO3 response = High BaTiO3 response

K

k

k

K

Direct magnetoelectric effect can be observed even in bilayers Significant effects visible only at temp. close to structural transitions.

80

81

next (?)

1. Interface coupling in multiferroic heterostructures: • Achieving reversible room-temperature E-switching of M in exchange-

biased structures, still pending.

• Anisotropy tuning by E-controlled strain works OK on piezo substrates. Less

successful in integrated heterostructures.

• In ferroelectric-gated structures, significant changes of M and TC obtained.

Mixed contributions of e-field and piezo response.

• However… for RT applications FM metals better than Oxides

2. Magnetically induced ferroelectricity: • Spinels, hexaferrites and other complex oxides: new famillies of materials

for FE response and H-sensitive even at RT.

• Ferroelectricity by spin-dependent P-d hybridization a new route to be

explored. Tinny effects (P) ?. Fast response ?

3. Domain walls • Dynamics of DW walls in multiferroic materials (YMnO3 or cycloidal);

coupling ?

• DW in ferromagnetic/antiferromagnetic insulators: new FE objects ?

0 100 200 300 400

15

20

25

30

35

r

Temperature (K)

T1

T2

0 100 200 300 400

10

100

r

Temperature (K)

T1

T2

T2 ’

T1 ’

T3’

BaTiO3 structural transitions

82

83

Magnetic spirals ferroelectrics: (Dy, Tb)MnO3

Magnetic field switching of polarization in magnetic

ferroelectrics

P ~ A eij x (Si x Sj)

Antisymmetric exchange

P

84

Summary

• Multiferroic heterostructures can be successfully used to

manipulate:

•the magnetization,

•the Curie temperature and

•the magnetic anisotropy of suitable ferromagnets

by using E-fields

• New multiferroic materials allow:

• (Fast) Switching of the Polarization even at RT

by using H-fields

• Domain walls in multiferroics:

• rather unknown objects that allow coupling of FM and FE

response.

85

Linear CO chain: the simplest case of Type-II MF

+ - + - + - + -

Direct exchange striction

Symmetric superexchange and striction

p p = 0 p

+ - + - + - + -

P

+ - + - + - + -

P

Date post:	02-Dec-2014
Category:	Small Business & Entrepreneurship
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