Zhe-Wen Song, Bang-Gui Liu
Double perovskite Bi$_2$FeCrO$_6$, related with BiFeO$_3$, is very interesting because strong ferroelectricity and high magnetic Curie temperature beyond room temperature are observed in it. However, existing density-functional-theory (DFT) studies, using pseudo-potentials, produce Mott-Hubbard ground state and hence low magnetic Curie temperature (below 130 K). Here, we optimize its crystal structure and then investigate its electronic structure and magnetic and optical properties by combining the full-potential augmented plane wave method with Monte Carlo simulation. Our optimized structure is a robust ferrimagnetic semiconductor. This nonmetallic phase is formed due to crystal field splitting and spin exchange splitting, in contrast to Mott-Hubbard states in previous DFT studies. Spin exchange constants and optical properties are calculated. Our ab initio magnetic Curie temperature is 450 K, much higher than previous DFT-based value and consistent with experimental results. Our study and analysis reveals that the main magnetic mechanism is an antiferromagnetic superexchange between Fe and Cr over the intermediate O atom. These results are useful to understanding such perovskite materials and others similar and exploring their potential applications.
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http://arxiv.org/abs/1210.5981
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