Papers by Author: Yu Jun Zhao

Abstract: The realization of ferromagnetism or ferrimagnetism in BiCrO3 is crucial for its potential application in magnetoelectronic devices. It is known from experiment that the antiferromagnetic monoclinic phase of BiCrO3 transits to orthorhombic as pressure beyond 1GPa. Here, we present a first-principles study of the magnetism of orthorhombic BiCrO3 under pressures up to 80GPa. We find that the energy difference between its ferromagnetic phase and the ground state of G-type anti-ferromagnetic phase becomes greater as the pressure increases, as well as the estimated magnetic transition temperature TN. This implies the difficulty of transforming BiCrO3 into ferromagnetism by external pressure, and thus other approaches (such as doping magnetic ions) are necessary to explore its potential application in magnetoelectronic devices.

Abstract: The electronic structure and magnetic properties of the (Co1-xFex)Tet(CoxFe2-x)OctO4 spinels (x is defined as the degree of inversion) scenario are investigated theoretically from first-principles, using generalized gradient approximation (GGA) method for the systems with strong coulomb correlations, which gives a correct description of the electronic structure. The GGA+U method gives an improved qualitative result compared with the GGA not only for the excited-state properties such as energy gaps but also for the ground-state properties such as magnetic moments and crystal parameters. The nominal valence of the transition metal elements and the ground state structure have been established based on the study of variation of the cation distribution (x=0.0, 0.25, 0.5, 0.75 and 1.0) over the tetrahedral and octahedral sites. The site-preference calculation on bulk systems indicates that Co2+ ions strongly prefer the octahedral B sites, and the electronic structure and magnetic properties of cobalt ferrites highly depend on the cation distributions even though the chemical composition of the compound does not change. The results are in good agreement with the available experimental data and most of the other theoretical results.