Direct Evidence for Multiferroic Magnetoelectric Coupling in0.9BiFeO3–0.1BaTiO3

Abstract

Magnetic, dielectric and calorimetric studies on 0.9BiFeO 3 -0.1BaTiO 3 indicate strong magnetoelectric coupling. XRD studies reveal a very remarkable change in the rhombohedral distortion angle and a significant shift in the atomic positions at the magnetic Tc due to an isostructural phase transition. The calculated polarization using Rietveld refined atomic positions scales linearly with magnetization. Our results provide the first unambiguous evidence for magnetoelectric coupling of intrinsic multiferroic origin in a BiFeO 3 based system.

Unambiguous evidence for magnetoelectric coupling of multiferroic origin in 0.73BiFeO3–0.27PbTiO3

“…The anomalies in the unit cell parameters ͑a m , b m , and ␤͒ and the unit cell volume ͑V m ͒ are clearly seen at T N , confirming the distortion of the lattice accompanying the dielectric anomaly due to the intrinsic multiferroic coupling via magnetoelastic effect. 11 To summarize, our studies on the BF-0.27PT system reveal anomalies in the intrinsic value of the dielectric constant, free from any space charge contributions, and also the unit cell parameters at the AFM transition temperature ͑T N ͒ as a result of multiferroic coupling. We have also shown that the so-called rhombohedral phase of BF-xPT ͑Refs.…”

“…It should also be supported by other auxiliary evidence such as magnetoelastic coupling in the bulk phase through structural studies. 11 Here, we present the results of magnetization, dielectric, and structural studies as a function of temperature on 0.73BiFeO 3 -0.27PbTiO 3 ͑BF-0.27PT͒ ceramics, which reveal monoclinic distortion of the ferroelectric phase and intrinsic coupling between the AFM and ferroelectric order parameters. The particular composition ͑x = 0.27͒ that we have investigated is of special interest as it corresponds to the highest value of x closest to the morphotropic phase boundary ͑MPB͒ in the BF-xPT system 15,16 before the structure transforms to the tetragonal phase.…”

“…7,8 It has been suggested that chemical substitutions may also suppress the cycloidal spin structure. [9][10][11] The observation of an anomaly in the temperature dependence of dielectric constant around the magnetic transition temperature is often taken as an evidence for magnetoelectric coupling. 12,13 However, a dielectric anomaly at the magnetic transition temperature can also result from the magnetoresistance effects in granular systems 14 because of the large difference in the resistivities of the grains and grain boundaries.…”

“…2 at two different temperatures, 473 K ͑i.e., at T N ͒ and 481 K ͑above T N ͒, distinctly show three separate semicircular arcs characteristic of electrode-grain interface ͑circle 1͒, grain boundary ͑circle 2͒, and grain contributions ͑circle 3͒ to the total polarization in the increasing order of frequency. 20 The observation of three distinct polarization processes is linked with the loss of oxygen during firing at high temperatures, 21,11 which can be written as…”

“…Such a polarization is expected to lead to the distortion of the lattice and hence anomalies in the unit cell parameters also. 11 To capture such anomalies, we have analyzed the powder diffraction data at various temperatures using Rietveld and Le Bail refinement techniques. Since the space group of the room temperature ferroelectric phase of BiFeO 3 is believed to be R3c, 5 we first considered this space group in our refinements.…”