Isostructural Phase Transition in BiFeO Solid Solutions BiFeO 3 - - PowerPoint PPT Presentation

Isostructural Phase Transition in BiFeO Solid Solutions BiFeO3 Solid Solutions

Dh j i P d Dhananjai Pandey

School of Materials Science and Technology Institute of Technology ,Banaras Hindu University, Varanasi

Email: dpandey_bhu@yahoo.co.in PhD Students:Anar Singh, Shuvrajyoti Bhattacharjee,BHU Neutron Scattering: Anatoliy Senyshyn and H Fuess SXRD: Y Kuroiwa, C Moriyoshi, K Taji M(T) data: R K Kotnala, V Pandey

PLAN

• Ferroic Order Parameters and Their Coupling in
• Ferroic Order Parameters and Their Coupling in

Multiferroics

• Contra-indication of Ferroelectricity and

Magnetism: Novel Mechanisms of Ferroelectricity g y

• Signatures of Magnetoelectric Coupling in Dielectric

g g g Studies in BiFeO3 Solid Solutions

• Evidence for Isostructural Phase Transition in

BiFeO3 Solid Solutions (Magnetoelectric Coupling , unusual tetragonality critical point large NTE) unusual tetragonality, critical point, large NTE)

Primary Ferroics

Ferroelectrics (FE): Spontaneous polarization (P) in the absence of electric field (E) Ferromagentics (FM): Spontaneous magnetization (M) in the absence of magnetic field (H) Ferroelastics (FS): Spontaneous strain (e) in the absence of stress (σ)

Antiferromagnetics and Antiferroelectrics are also considered as (Anti-) Ferroics

Ferroelectricity Ferromagnetism F l i i

g ( )

Switchable spontaneous P/M/e by E/H/σ Ferroelectricity Spontaneous polarization Ferromagnetism Spontaneous magnetization Ferroelasticity Spontaneous strain

Magnetoelectric Effect (ME) in Multiferroics

Coupling of primary order parameters ( P & M ) in Multiferroics

Free energy of magnetoelectric materials

Coupling of primary order parameters ( P & M ) in Multiferroics

• F(Ei , Hj) = 1/20ijEiEj +1/20ij HiHj+ ij EiHj +(1/2)ijkEiHjHk

+(1/2)ijkEiEjHk electric polarization: P(H) = - dF / dE magnetization: M(E) = - dF / dH

• Linear magnetoelectric effect:

Pi = ij Hj ; Mj = ij Ej

• Higher order couplings for   0,   0

P t ti l T h l i l li ti Potential Technological applications

Novel sensors and actuators New Four State Logic System Information storage technology (write electrically and read magnetically)

ABO3 Perovskite Structure ABO3 Perovskite Structure “d0 vs dn paradox”

A O Ferroelectricity PbTiO3,BaTiO3 &

B

3, 3

• ther Perovskites :

3d0 of Ti 4+ & 2p 3d0 of Ti 4 & 2p

• f O 2- hybridize

M ti Magnetism Partially filled d band

Novel Mechanisms of Inversion Symmetry Breaking in Multiferroics ((A)FM+FE)

• 1. Lone pair stereochemistry of A site atom for FE

and d electrons of B atom for FM/AFM in ABO3, eg BiMnO BiFeO (Hill J Phys Chem B (2000))

• eg. BiMnO3, BiFeO3 (Hill, J Phys Chem B (2000))
• 2. Geometric ferroelectricity: Structural instability in
• 2. Geometric ferroelectricity: Structural instability in

magnetic compounds, eg. YMnO3, InMnO3 (hexagonal) (Van Aken et al Nature Mat 3 164 (2004)) (Van Aken et al, Nature Mat. 3, 164 (2004)). 3 Magnetic Ferroelectrics: Spin spiral as a source 3. Magnetic Ferroelectrics: Spin spiral as a source

• f electric polarization in magnetic compounds,
• eg. TbMnO3, DyMnO3 (Kimura et al, Nature ,2003),

CaMn O (Johnson et al PRL 2012) CaMn7O12 (Johnson et al PRL 2012) 4. Charge ordering

BiFeO3 : The only RT Multiferroic

Multiferroic with the highest ordering temperatures Ferroelectric TC= 1103K Antiferromagnetic TN= 643K

Structure of BiFeO3

• R3c space group.
• The cations are displaced along the [111] direction relative to the

anions.

• Anti-phase rotated neighbouring oxygen octahedra about [111] due

to an antiferrodistortive transition involving R (q = 1/2 1/2 1/2) point to an antiferrodistortive transition involving R (q = 1/2 1/2 1/2) point phonon.

• Trigger type transition ( Singh , Patel and Pandey, APL 2010)

[111] Bi Bi Fe O

• A. J. Jacobson and B. E. F. Fender, J. Phys. C 8,844 (1975)

Magnetic structure of BiFeO3

Ferromagnetically coupled Fe moments within the (111) plane and antiferromagnetic coupling between adjacent planes : G-type antiferromagnetic ordering (wrt the planes : G type antiferromagnetic ordering (wrt the perovskite cell).

• Plane of spin orientation is (1-10)
• Incommensurate modulated spin structu
• Long period wavelength ~620 A

g p g

• Propagation vector q is along [110]
• Inhibits the linear magnetolelectric effect
• I. Sosnowaska et al., J. Phys. C 15,4835 (1982)

BiFeO3 Single Crystal

Remnant polarization Ferroelectric hysteresis (P-E) loop Remnant polarization Pr [012]~60 to 100 C/cm2 Coercive field ~12 kV/cm Magnetization curve versus applied magnetic field

(D.Lebeugle et al., Appl. Phys. Lett. 91, 022907 2007)

Magnetic field perpendicular to (012) plane at different temperatures

D.Lebeugle et al., PRB 2007

Epitaxial BiFeO3 Multiferroic Thin Film

Ferroelectric hysteresis loop measured at 15 kHz for 200 nm thick film: Remnant Polarization ~ 55C/cm2) Magnetic hystersis (M-H) loop for a 70nm BFO film: Spin spiral melting Saturation magnetization ~150emu/cm3

(controversial result)

Coercive field ~200Oe Linear magnetoelectric (ME) effect was reported: Melting of spin spiral

• J. Wang et al., Science 299, 1719 (2003)

Magnetoelectric Coupling of Intrinsic Multiferroic Origin in 0.9BiFO3-0.1BaTiO3 Origin in 0.9BiFO3 0.1BaTiO3

Anar Singh

Can disorder in the magnetic sublattice suppress the spatial modulation of the spins and release the latent magnetisation?

Physical Review Letters 101,247602 (2008)

Rietveld fit for 0.9BiFeO3-0.1BaTiO3 using R3c space group

sity (a.u.) Intens 2 0 4 0 6 0 8 0 1 0 0 1 2 0 2  ( d e g r e e s )

Magnetic study

M ti h t i (M H) l

0.075 0.150

Magnetic hystersis (M-H) loop

• Weak ferromagnetism unlike pure BiFeO

0 150

• 0.075

0.000 M(emu/g)

• Weak ferromagnetism unlike pure BiFeO3
• Spin spiral ordering may be suppressed
• 6
• 4
• 2

2 4 6

• 0.150

H(KOe)

Inverse of magnetic susceptibility vs. temperature Magnetic transition temperature

6 8 10

/emu)

Magnetic transition temperature Tc = 648 K

2 4 6

1/ (10

5 g Oe/

Singh et al , Phys. Rev. Lett. 101, 247602 (2008)

300 400 500 600 700

Temperature (K) 1

Tc

Dielectric study: Magnetoelectric coupling ?

10

1-1kHz

6 8

4 3 2 1

2)

2-10kHz 3-50kHz 4-100kHz 5-300kHz 6-500kHz 7 700kH

4 6

8 7 6 5 4 ' (1 7-700kHz 8-4MHz

For frequencies > 300 kHz

• T/

m nearly coincides with the magnetic transition

temperature TC ~648 K

• Grain (intrinsic) contribution linked with

300 350 400 450 500 550 600 650 700 750 2

Temperature (K)

• Grain (intrinsic) contribution linked with

magnetoelectric coupling

3 6 Ohm) (b) T=575K 10KHz 50KHz 100KHz 300KHz 500KHz 1MHz

Grain Grain boundary

• 3

Z'' (10

3

Grain boundary Electrode-grain interface

3 6 9 12 15 3 Z' (10

3 Ohm)

Singh et al, Phys. Rev. Lett. 101, 247602 (2008)

Magneto-elastic coupling in BF-0.10BT

• Rhombohedral distortion angle

ee)

• Rhombohedral distortion angle
• Unit cell volume

59.40 126.5 127.0

3)

e (degre

59.38 126.0

ume (Å

3

al angle

59.36 125 0 125.5

Volu bohedra

300 400 500 600 700 800 900 125.0

Tc

Rhom Temperature (K) p ( )

Singh et al.,Phys. Rev. Lett. 101, 247602 (2008)

Temperature Dependence of Atomic Positions (Isostructural Phase Transition)

0.2072 0.2080 0.224

O x z

0.2064 0.220 0.345

Bi

0 0168

• 0.0165

0.343 0.344

O y Fe z

300 500 700

• 0.0171
• 0.0168

300 500 700 0.342 0.343 Tc Tc 300 500 700 300 500 700

Temperature (K)

In the magnetic phase: In the magnetic phase: ZBi (i.e. Z300 K-Z700 K)~ 0.038 Å

Singh et al , Phys. Rev. Lett. 101, 247602 (2008)

Atomic displacements of IR(1) mode for Bi

Bi

Atomic displacements of IR(1) mode for Fe

Fe

Atomic displacements of IR(1) mode for O

O

Temperature dependence of ionic polarization (P)

d Z P

natom i i i





Zi: nominal charge of ith atom di: shift of ith atom

V P

ionic 

i

V: volume of the cell

57.0 56.5

C/cm

2)

55.5 56.0

P (

Tc 300 400 500 600 700 800

Temperature (K)

Singh et al, Phys. Rev. Lett. 101, 247602 (2008)

Evidence for linear magnetoelectric coupling

• P scales linearly with M

S t i f th ti i l d ?

• Suggests suppression of the magnetic spiral order?

57.0 56 0 56.5

C/cm

2)

0.024 0.032 0.040 0.048 0.056 55.5 56.0

P ( M (emu/g)

Singh et al, Phys. Rev. Lett. 101, 247602 (2008)

Magnetoelectric Coupling of Intrinsic Multiferroic Origin in 0.8BiFO3-0.2BaTiO3: A Neutron Powder Diffraction Study A Si h t l Anar Singh et al Phys Rev B (2011) y ( ) Oxygen positions Magnetisation g

Evolution of Neutron Powder Diffraction Patterns of BF-0.20BT with Temperature

Magnetic peak

*

s)

400 K 350 K 300 K

y (arb. unit

575 K 550 K 500 K 450 K 400 K * * *

Intensity

700 K 650 K 625 K 600 K 575 K * *

20 40 60 80 100 2 (degrees)

Magnetic Transition Temperature

400

I=I0(1-T/Tc)

2

I0=953+30 T 520+5

nsity 200

Tc=520+5

= 0.52+0.04

rated Inten 4

=0(1-T/Tc)



0=5.5+0.1

B)

Integ 2

0

Tc=515+5 =0.53+0.04

t per Fe (B 200 400 600 Moment 200 400 600 Temperature (K)

The decomposition of the

(a)

1

The decomposition of the magnetic representation  in terms of irreducible representations  for the 6a

20 30 40 RMag=2.32 Rwp=3.23, 

2=2.15

representations k for the 6a site is as follows :

(b)

2

• b. units)

2 3 1 2 1 1

2 1 1 ) / 6 (        Fe a

20 30 40 RMag= 7.30 Rwp=11.1, 

2=24.9

ntensity (arb In

(c)

3

20 30 40 RMag=2.45 Rwp=3.21,

2=2.11

20 40 60 80 100 120 2 (degrees)

Magnetic Structure of BF-0.2BT

(a) (b) [001]h

Structural and magnetic parameters for BF-0.2BT pattern at room temp

• btained after the Rietveld refinement of the high resolution NPD pattern (FRM II)

with wavelength =1.54Ǻ corresponding to representation 3 Atom x y z B(Å2) Bi/Ba 0 0 0.2905(2) 2.38(5) Fe/Ti 0 0 0.0154(2) 0.57(4) O 0.2130(3) 0.3454(3) 0.083333 1.59(4) ( ) ( ) ( ) Bi/Ba(Å2):11= 22= 212= 0.0157(3), 33= 0.0029(1) O(Å2): 11= 0.0209(7), 22= 0.0118(5), 33= 0.0021(1) 12= 0.0077(6), 13= -0.0026(3), 23= -0.0023(2) 12 0.0077(6), 13 0.0026(3), 23 0.0023(2) Bi-O1(×3)= 3.340(3) Bi-O2(×3)= 3.082(2) Bi-O3(×3)= 2.639(2) Bi-O4(×3)= 2.358(3) Fe-O1(×3)= 1.938(2) Fe-O2(×3)= 2.091(3) a= 5.60785(2), c= 13.90109(4), =1200, Fe=3.27(6) Rwp= 3.21, 2= 2.11, RMag=2.45

wp

,  ,

Mag

Isostr ct ral Phase Transition in BF 0 20BT Isostructural Phase Transition in BF-0.20BT

0 286 0.288 0.21 Ox iz 0.284 0.286 0 015 0.20 Bi 0.014 0.015 0 342 0.344 Fez Oy 400 600 0.013 400 600 0.342 Temperatrue (K) Temperatrue (K)

Magnetoelectric Coupling in BF-0.20BT

60 54 57 (a) /cm2) (c) 58 51 54 C/cm2) P (C/ 56 600 700 P (C (b)

/

1 2 3 56 500 600 700 500



M (B) Temperature (K)

CONCLUSIONS CONCLUSIONS

• Evidence for Isostructural Phase

Evidence for Isostructural Phase Transition leading to Magnetoelectric Coupling of Intrinsic Multiferroic Origin in Coupling of Intrinsic Multiferroic Origin in BF-BT

• Key Role of Crystallographic Tools in

R li thi C li t th t i l l Revealing this Coupling at the atomic level

Isostructural Phase Transition in ( ) O ( ) O (1-x) BiFeO3-(x) PbTiO3

Multiple instabilities ( MPB, AFD, Magnetic, Stress- induced transition) Stress induced transition)

• Unusually large tetragonality (

19%)

• Unusually large tetragonality (~ 19%)
• Negative Thermal Expansion

C iti l P i t

• Critical Point

Shuvrajyoti Bhattacharjee

Bhattacharjee, Taji, Moriyoshi, Kuroiwa and Pandey, Phys. Rev. B, 84,104116 (2011)

x=0.31

1 10 101 11

Tetragonal

Morphotropic Phase Transition

T 100 T 001 T11 T1 T002 T1

x=0.30

Tetragonal

* ** * *

x=0.29

(arb.units.)

* ** ** *

x=0.28

** *

Intensity

T + M

T T T T

*

x=0.27

c 100 c 110 c 111

1/2 3/2 -1/2

Monoclinic/Pseudo-rhombohedral

Bhattacharjee, Tripathi and Pandey, Appl.Phys.Lett, 91, 042903(2007)

20 24 30 33 38 40 2 (degrees)

x= 0.31

rb.units)

units)

110 101

31 32 33

Intensity (ar

nsity (arb.u

1

Tetragonal

20 40 60 80 100 31 32 33 Inte 2 (degrees)

x = 0 . 2 7

its) nsity (arb. un

Monoclinic

2 0 4 0 6 0 8 0 1 0 0 1 2 0

Inten

Monoclinic

2  ( d e g r e e s )

Bhattacharjee, Pandey, Kotnala and Pandey, Appl.Phys.Lett, 97, 262506 (2010) Bhattacharjee, Tripathi and Pandey, Appl.Phys.Lett, 91, 042903(2007)

MPB

4.4 4.6 126 127

(A)



4.2 4.4 125 Monoclinic (Cc)

• nal

mm)

parameter ( (degree)

c 4.0 123 124 Tetrag (P4m

Lattice p

aP

Angle

a 10 20 30 40 50 60 70 80 90 100 3.8 122 bP

cP

10 20 30 40 50 60 70 80 90 100

Composition (% in PbTiO3)

P║ [001] for Tetragonal ; P ~ ║ <112> for Monoclinic

Bhattacharjee and Pandey, J. Appl. Phys. 107,124112 (2010)

P║ [001] for Tetragonal ; P ║ <112> for Monoclinic

0 20

Unusually large tetragonality ~ 19%

0.18 0.20 ty 0.14 0.16 gonalit 0 10 0.12 0.14 ) Tetra 0.08 0.10 (c/a-1 20 30 40 50 60 70 80 90 100110 0.06

x

20 30 40 50 60 70 80 90 100110 Composition (% in PbTiO3)

x

Magnetic Transitions in BF-xPT

0003

0.004 x=0 31

Monoclinic Tetragonal

0.002 0.003 x=0.25

• le-1Oe-1)

0.003 e-1-Oe-1) x=0.31

0.001 0.003 x=027 n (emu-mo

0.006 x=0 40 (emu-mole

0001 0.002 x=0.27 gnetisation

0.004 x 0.40 agnetisation

400 500 600 0.001 Mag

200 400 Ma

Tem perature (K )

200 400 Temperature (K)

Antiferromagnetic Transition

Monoclinic x= 0 25 Tetragonal x=0 31

(b) (a)

10P 00P 0-2

BF-0.25PT

Monoclinic x= 0.25 Tetragonal x=0.31

300K 250K

• b. units)

1 10 10-1, 20 600K 550K

. units) 250K 200K 180K 160K 120K 140K Intensity (arb

550K 525K 500K 475K 450K

ntensity (arb. 120K 100K 80K 60K 40K

450K 425K 325K 375K 400K

In 24 27 30 33 20K 2 (degree) 20 30

325K 300K

2 (degree)

Variation of TN

600

PB

600

MP

re (K) 400

M T

peratur 200 Tem 00 02 04 06 08 10 0.0 0.2 0.4 0.6 0.8 1.0 Composition (x)

x= 0 25

(a) (X10

2)

x= 0.31

(b)

Cc (PM)

(c)

x= 0.25 T=673K

units)

T= 300K ) (PM) P4mm (PM)

6

T=300K

y (arb. u TN(K)

r AFM) T= 20K mm pe AFM)

*

ntensity

collinear

3

P4 Cc (G- typ

In

(Non c

*

C

20 30 25 30 0.0 0.2 0.4 2 (degree) Composition (x) ( g ) p ( )

Bhattacharjee, Pandey, Kotnala and Pandey, Appl.Phys.Lett, 97, 262506 (2010)

Magnetic Structures : Neutron Diffraction

For Monoclinic (Cc) compositions, Fe 3+ occupies 4a Wyckoff site For Monoclinic (Cc) compositions, Fe

• ccupies 4a Wyckoff site

4a =3[1 + 2] For tetragonal (P4mm) compositions, Fe3+ occupies 1b Wyckoff site 1b = 3 + 5

x=0.25 Monoclinic x=0.31 Tetragonal Tetragonal Bhattacharjee, Senyshyn, Krishna, Fuess and Pandey, Appl.Phys.Lett, 97, 262506 (2010)

Bhattacharjee, senyshen, Krishna, Fuess and Pandey, Appl.Phys.Lett, 97, 262506 (2010)

Isostructural Tetragonal to Tetragonal Isostructural Tetragonal to Tetragonal Phase Transition in BF-xPT

Bhattacharjee, Taji, Moriyoshi, Kuroiwa and Pandey, Phys. Rev. B, 84,104116 (2010)

48K T=84 Bhattacharjee, Taji, Moriyoshi, Kuroiwa and Pandey, Phys. Rev. B, 84,104116 (2011)

Bhattacharjee, Taji, Moriyoshi, Kuroiwa and Pandey, Phys. Rev. B, 84,104116 (2011)

Bh tt h j T ji M i hi K i d P d Ph R B 84 104116 (2011) Bhattacharjee, Taji, Moriyoshi, Kuroiwa and Pandey, Phys. Rev. B, 84,104116 (2011)

Bhattacharjee, Taji, Moriyoshi, Kuroiwa and Pandey, Phys. Rev. B, 84,104116 (2010)

Bhattacharjee, Taji, Morisoi, Kuriowa and Pandey, Phys. Rev. B, 84,104116 (2010)

Bhattacharjee, Taji, Moriyoshi, Kuroiwa and Pandey, Phys. Rev. B, 84,104116 (2010)

Summary Summary

• Evidence for Isostructural Phase

T iti (IPT) i BF BT d BF PT Transitions (IPT) in BF-xBT and BF-xPT

• Magnetoelectric coupling arises due to IPT
• Unusually large tetragonality in BF-xPT

system is also due to an IPT y