Spin and structural transitions in AlFeO3 and FeAlO3 perovskite and post- perovskite

We use an advanced formalism within the density functional theory to investigate the perovskite and post- perovskite structures with AlFeO3 chemistry. We consider two ordered cases: one with Fe and then one with Al in octahedral coordination. For each case we investigate several spin configurations. We observe that up to 90 GPa the FeAlO3 perovskite structure, i.e. with Fe3+ in the inter-octahedral space, with antiferromagnetic configuration and large local magnetic moment is the most stable one. Beyond 90 GPa the post-perovskite structure of AlFeO3, i.e. with Fe3+ in octahedral coordination, with antiferromagnetic configuration and small local magnetic moment is the most stable one. The perovskite to post-perovskite phase transition at 90GPa triggers a partial collapse of the magnetic moment. The local magnetic moment vanishes beyond 150 GPa in post-perovskite.