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

Isostructural Phase Transition in BiFeO Solid Solutions BiFeO 3 Solid Solutions Dh Dhananjai Pandey j i P d 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 BiFeO 3 Solid Solutions • Evidence for Isostructural Phase Transition in BiFeO 3 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 g ( ) Switchable spontaneous P/M/e by E/H/ σ Ferroelectricity Ferroelectricity Ferromagnetism Ferromagnetism F Ferroelasticity l i i Spontaneous Spontaneous magnetization Spontaneous strain polarization

Magnetoelectric Effect (ME) in Multiferroics Coupling of primary order parameters ( P & M ) in Multiferroics Coupling of primary order parameters ( P & M ) in Multiferroics Free energy of magnetoelectric materials - F(E i , H j ) = 1/2  0  ij E i E j + 1/2  0  ij H i H j +  ij E i H j +(1/2)  ijk E i H j H k +(1/2)  ijk E i E j H k electric polarization: P(H) = - dF / dE magnetization: M(E) = - dF / dH P i =  ij H j ; M j =  ij E j • Linear magnetoelectric effect: • Higher order couplings for   0,   0 Potential Technological applications P t ti l T h l i l li ti Novel sensors and actuators New Four State Logic System Information storage technology (write electrically and read magnetically)

ABO 3 Perovskite Structure ABO 3 Perovskite Structure “d 0 vs d n paradox” A Ferroelectricity O PbTiO 3 ,BaTiO 3 & 3 , 3 other Perovskites : B 3d 0 of Ti 4+ 3d 0 of Ti 4 & 2p & 2p of O 2- hybridize M Magnetism ti 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 ABO 3 , eg BiMnO eg. BiMnO 3 , BiFeO 3 (Hill, J Phys Chem B (2000)) BiFeO (Hill J Phys Chem B (2000)) 2. Geometric ferroelectricity: Structural instability in 2. Geometric ferroelectricity: Structural instability in magnetic compounds, eg. YMnO 3 , InMnO 3 (hexagonal) (Van Aken et al Nature Mat 3 164 (2004)) (Van Aken et al, Nature Mat. 3, 164 (2004)). 3 3. Magnetic Ferroelectrics: Spin spiral as a source Magnetic Ferroelectrics: Spin spiral as a source of electric polarization in magnetic compounds, eg. TbMnO 3 , DyMnO 3 (Kimura et al, Nature ,2003 ), CaMn O CaMn 7 O 12 (Johnson et al PRL 2012) (Johnson et al PRL 2012) 4. Charge ordering

BiFeO 3 : The only RT Multiferroic Multiferroic with the highest ordering temperatures Ferroelectric T C = 1103K Antiferromagnetic T N = 643K

Structure of BiFeO 3 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 BiFeO 3 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)

BiFeO 3 Single Crystal Ferroelectric hysteresis (P-E) loop Remnant polarization Remnant polarization P r [012] ~60 to 100  C/cm 2 Coercive field ~12 kV/cm (D.Lebeugle et al., Appl. Phys. Lett. 91, 022907 2007) Magnetization curve versus applied magnetic field Magnetic field perpendicular to (012) plane at different temperatures D.Lebeugle et al., PRB 2007

Epitaxial BiFeO 3 Multiferroic Thin Film Ferroelectric hysteresis loop measured at 15 kHz for 200 nm thick film: Remnant Polarization ~ 55  C/cm 2 ) Magnetic hystersis (M-H) loop for a 70nm BFO film: Spin spiral melting Saturation magnetization ~150emu/cm 3 (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 0.9BiFO 3 -0.1BaTiO 3 Origin in 0.9BiFO 3 0.1BaTiO 3 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 0.9BiFeO 3 -0.1BaTiO 3 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 Magnetic hystersis (M-H) loop M ti h t i (M H) l 0.150 0.075 • Weak ferromagnetism unlike pure BiFeO 3 • Weak ferromagnetism unlike pure BiFeO M(emu/g) 0.000 • Spin spiral ordering may be suppressed -0.075 -0.150 0 150 -6 -4 -2 0 2 4 6 H(KOe) Inverse of magnetic susceptibility vs. temperature 10 /emu) 8 Magnetic transition temperature Magnetic transition temperature 6 6 5 g Oe/ T c = 648 K 4 1/  (10 2 1 0 300 400 500 600 700 Tc Temperature (K) Singh et al , Phys. Rev. Lett. 101, 247602 (2008)

Dielectric study: Magnetoelectric coupling ? 10 1-1kHz 1 2-10kHz 3-50kHz 8 4-100kHz 2 5-300kHz 6-500kHz 3 2 ) 0 7-700kHz 7 700kH  ' (1 6 6 4 4 For frequencies > 300 kHz 5 8-4MHz 6 7 • T / m nearly coincides with the magnetic transition 8 4 temperature T C ~648 K • Grain (intrinsic) contribution linked with • Grain (intrinsic) contribution linked with magnetoelectric coupling 2 300 350 400 450 500 550 600 650 700 750 Temperature (K) 100KHz 300KHz T=575K (b) 500KHz 6 50KHz Grain 1MHz Ohm) 10KHz Grain boundary Grain boundary 3 3 Z'' (10 Electrode-grain interface 0 -3 3 0 3 6 9 12 15 3 Ohm) Z' (10 Singh et al, Phys. Rev. Lett. 101, 247602 (2008)

Magneto-elastic coupling in BF-0.10BT • Rhombohedral distortion angle • Rhombohedral distortion angle • Unit cell volume ee) e (degre 127.0 59.40 126.5 3 ) al angle 3 ume (Å 59.38 126.0 bohedra Volu 125.5 59.36 125.0 125 0 Rhom 300 400 500 600 Tc 700 800 900 Temperature (K) p ( ) Singh et al.,Phys. Rev. Lett. 101, 247602 (2008)

Temperature Dependence of Atomic Positions (Isostructural Phase Transition) 0.2080 0.224 O x z 0.2072 Bi 0.220 0.2064 0.345 -0.0165 0.344 Fe z O y 0.343 0.343 -0.0168 0 0168 0.342 Tc Tc -0.0171 300 300 500 500 700 700 300 300 500 500 700 700 Temperature (K) In the magnetic phase: In the magnetic phase:  Z Bi (i.e. Z 300 K -Z 700 K )~ 0.038 Å Singh et al , Phys. Rev. Lett. 101, 247602 (2008)

Atomic displacements of IR(1) mode for Bi Bi

Fe Atomic displacements of IR(1) mode for Fe

O Atomic displacements of IR(1) mode for O

Temperature dependence of ionic polarization (P) natom  Z i : nominal charge of ith atom Z d i i d i : shift of ith atom ionic   i P P i V: volume of the cell V 57.0 2 )  C/cm 56.5 P (  56.0 55.5 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 • Suggests suppression of the magnetic spiral order? S t i f th ti i l d ? 57.0 2 ) 56.5  C/cm P (  56 0 56.0 55.5 0.024 0.032 0.040 0.048 0.056 M (emu/g) Singh et al, Phys. Rev. Lett. 101, 247602 (2008)

Magnetoelectric Coupling of Intrinsic Multiferroic Origin in 0.8BiFO3-0.2BaTiO 3 : A Neutron Powder Diffraction Study A Anar Singh et al Si h t l Phys Rev B (2011) y ( ) Oxygen positions Magnetisation g

Evolution of Neutron Powder Diffraction Patterns of BF-0.20BT with Temperature Magnetic peak * s) y (arb. unit 300 K 350 K 400 K 400 K Intensity 450 K 500 K * 550 K * 575 K 575 K * * 600 K * 625 K 650 K 700 K 20 40 60 80 100 2  (degrees)

Magnetic Transition Temperature 2  I=I 0 (1-T/T c ) nsity I 0 =953+30 400 rated Inten T c =520+5 T 520+5  = 0.52+0.04 200 Integ 0   =  0 (1-T/T c ) 4  0  0 =5.5+0.1 B ) t per Fe (  B T c =515+5  =0.53+0.04 2 Moment 0 200 200 400 400 600 600 Temperature (K)