Bonding and Electronic Properties of BiFeO3 Multiferroic Material (original) (raw)
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The Journal of Chemical Physics, 2009
BiFeO 3 has attracted great interest for its multiferroic property. The spontaneous electric polarization, multiferroism, and static magnetoelectric coupling have been widely studied both experimentally and theoretically. Here, in this paper, we report on the effects of magnetic ordering, spin fluctuation, and external magnetic field on the linear dielectric function and second-harmonic generation ͑SHG͒ in multiferroic BiFeO 3. First, our generalized gradient approximation plus Hubbard U calculations reproduce very well experimental data of linear dielectric function. In the mean time, it is revealed that SHG susceptibilities differ dramatically between antiferromagnetic configuration and ferromagnetic one, which is due to the enhanced contrast in the double-photon resonance absorption. Further Monte Carlo simulation of the coupling between electric order and spin-pair correlation function is presented for the spin fluctuation dependence of SHG. The significant nonlinear optical magnetoelectric effect around the Néel temperature provides novel route to enhancing magnetoelectric coupling in multiferroic materials.
Intrinsic defects in multiferroic BiFeO_{3} and their effect on magnetism
Physical Review B, 2012
We investigate the energetics of the intrinsic defects in bulk multiferroic BiFeO 3 and explore their implication for magnetization using a first-principles approach based on density functional theory. We find that the dominant defects in oxidizing (oxygen-rich) conditions are Bi and Fe vacancies and in reducing (oxygen-poor) conditions are O and Bi vacancies. The calculated carrier concentration shows that the BiFeO 3 grown in oxidizing conditions has p-type conductivity. The conductivity decreases with oxygen partial pressure, and the material becomes insulating with a tendency for n-type conductivity. We find that the Bi and Fe vacancies produce a magnetic moment of ∼1μ B and 5μ B per vacancy, respectively, for p-type BiFeO 3 and none for insulating BiFeO 3 . O vacancies do not introduce any moment for both p-type and insulating BiFeO 3 . Calculated magnetic moments due to intrinsic defects are consistent with those reported experimentally for bulk BiFeO 3 .
Magnetic and electrical properties of single-phase multiferroic BiFeO< sub> 3
2005
Abstract We have reported the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO 3 ceramics synthesized by a rapid liquid-phase sintering technique. Optimum conditions for the synthesis of single-phase BiFeO 3 ceramics were obtained. Temperature-dependent magnetization and hysteresis loops indicate antiferromagnetic behavior in BiFeO 3 at room temperature.
Magnetic and Dielectric Studies on Cobalt Substituted BiFeO3
2015
This thesis presents the study of structural, surface morphology, electric, magnetic, magnetoelectric and magnetodielectric properties of Cobalt substituted multiferroic BiFeO3. Since their discovery, multiferroics have brought tremendous interest among the researchers due to the coexistence of various ferroic order parameters. The synchronization of the magnetic and electric order parameter, hence generating magnetoelectric coupling, has been of importance in particular. Various functional devices aiming at the coupling between the ferroelectric and ferromagnetic order parameter are underway. Among all, the perovskite oxides (ABO3) based multiferroics are of prime interest due to their ease of synthesis and easy to understand physical interactions due to their simple structure. Bismuth Ferrite (BiFeO3), is a prototype ABO3 type multiferroic material, possessing the ferroelectric Curie temperature (Tc) ~ 1103K and antiferromagnetic Neel temperature (TN) ~ 643K. It exhibits a weak ne...
Ab-initio study of competing magnetic configurations in cubic BiFeO3 alloys
Journal of Magnetism and Magnetic Materials, 2011
Using ab-initio calculations, we study the properties of the multiferroic BiFeO 3 compounds in the perfect cubic perovskite lattice structure. We show that the appearance of magnetism is energetically favorable. Except the ferromagnetic structure, there are three possible antiferromagnetic arrangements, which are close in energy, and for large values of the lattice constant a G-type antiferromagnetism is the most stable magnetic order. Fe atoms are responsible for the spin magnetic moments while the values of the induced spin moments at the other sites depend strongly on the local environment of the atoms. There is a significant charge transfer from the Fe and Bi atoms towards the p-states of O atoms.
The solid solution of (1 − x)BiFeO3-xDyFeO3 was prepared by solid state reactions in the form of ceramics. The effects of chemical modification by means of aliovalent ionic substitution of Ti 4+ for Fe 3+ on the structure and dielectric properties were investigated. A morphotropic phase boundary bridging the perovskite rhombohedral phase and the orthoferrite orthorhombic phase was identified at x around 0.1. The chemical modification was found to stabilize the perovsite phase. The dielectric performance of the solid solution was improved by the substitution of Ti 4+ for Fe 3+ , which decreased the electric conductivity by reducing oxygen vacancies, as evidenced by the decrease in loss tangent values. Magnetic hysteresis and large saturated magnetization (0.5 μB/f.u.) were realized in 0.92BiFeO3-0.08DyFeO3 with 2% substitution of Ti 4+ for Fe 3+ , which is believed to arise from the disruption of the spiral spin modulation after structural modification, and the interaction between the spins of the Dy 3+ and Fe 3+ at low temperatures which decouples the antiferromagnetic order between the Fe 3+ ions.
Structurally tuned multiferroic state in BiFeO3-based compounds
Applied Physics A, 2012
Structurally tuned multiferroic state is demonstrated for BiFeO 3-based compounds. The electric and magnetic orders are strongly affected by the coexistence of R3c and Cm phases, i.e., by structural softness through monoclinicity, which leads the multiferroism to be driven by the same cation. The Cm phase enhances the ferroelectric and magnetic responses through Bi/Ba-O and Fe/Ti-O bonds by influencing structural distortions and ion valence. We also show the strong correlations between ferroic orders, structural arrangements, and tuning of the ion valence in the perovskite B site.