Electronic structure and magnetic properties of SrFe1−xMnxO2: A theoretical investigation

We investigate the electronic structure and magnetic properties of SrFe1−xMnxO2 system using first-principles calculations and the site-random Heisenberg model. Calculations show that the ground state of SrFe1−xMnxO2 with x≤0.3 is a Mott insulator. The ground state of SrFe0.875Mn0.125O2 has the same (πππ) ordered antiferromagnetic state as in the undoped compound. For SrFe0.75Mn0.25O2, the (πππ) as well as the (ππ0) ordered antiferromagnetic state may exist depending on the atomic configuration. The magnetic structure and its change by doping can be explained based on the estimated interlayer exchange interactions. The effects due to random distributions of Fe and Mn ions are investigated by Monte Carlo simulations based on the site-random Heisenberg model with exchange parameters obtained from first principles calculations. The results show that the Néel temperature TN corresponding to the phase transition from the paramagnetic phase to the (πππ) ordered phase decreases with increasing x, and a second transition from the (πππ) ordered phase to a mixed phase with coexistence of both the (πππ) and (ππ0) orderings develops at TN′ below TN.