Magnetism, half-metallicity and bonding in AlFeO<inf>3</inf> and the impact of In-doping

AlFeO3 is a ferroelectric perovskite material and attempts have been made to study its magnetic properties. However there is no consensus currently on the precise nature of magnetic ordering (antiferromagnetism Vs. ferrimagnetism) in this material. Considering the recent report on band gap tunability of Al1−xInxFeO3 (Sudha Priyanga and Tiju Thomas, J. Alloys. Compd. 750 (2018) 312–319), there is reason to explore the nature of magnetism and bonding, in the parent AlFeO3 system, and its In-doped variants. Here, we analyze the magnetic behavior of this system using first principles calculations. It is found that ferrimagnetic orthorhombic phase of AlFeO3 is the most stable form at normal pressure, consistent with the experiment reported recently. The calculated total magnetic moment of AlFeO3 in orthorhombic phase is 3.97 µB and it is comes from the exchange interaction arising between Fe and oxygen atoms, which in turn leads to ferrimagnetic ordering in the system. The calculated magnetic moment decreases with an increase in In-dopant concentration in Al1−xInxFeO3 (x = 0.25, 0.5, 0.75). Electronic structure reveals that both cubic and rhombohedral phases of AlFeO3 exhibit ferromagnetic and half metallic natures respectively. It is hence evident that ferrimagnetic ordering and half-metallicity of the cubic and rhombohedral phases is rather robust in this system. Charge density distribution, Bader charge analysis, and maximum electron localization function based evaluation shows that the bonding in AlFeO3 is primarily ionic. Interestingly the nature of Fe–O bond is rather invariant with respect to In concentration. Experimental evidence for the results reported (magnetic ordering, nature of bonding) may be pursued here on.