Effect of isovalent non-magnetic Fe-site doping on the electronic structure and spontaneous polarization of BiFeO_3

摘要

We report the results of our first-principles calculations on the effect of isovalent, non-magnetic, Al~(3+) ion doping on the electronic structure and spontaneous polarization of multiferroic BiFeO_3. Our calculations reveal that Al~(3+) doping in BiFeO_3 results in the reduction of Fe-O-Fe bond angle, leading to the weakening of antiferromagnetic superexchange interaction, further substantiated by the reduction of exchange interaction constant with increasing doping level. Lowering of well-depth is suggestive of reduced switching potential and improved P-E loop with lowered coercivity. Chemical bonding analysis by electron localization function shows that cation-oxygen bonding is of mixed ionic-covalent character, with marginal increase in the covalent character with increasing doping concentration. Large spontaneous polarization of undoped BiFeO_3 is retained with lower doping level (6.25%), while for higher doping content (31.25%), the spontaneous polarization is reduced, primarily due to larger c/a ratio at higher doping level.