Magnetic Phase Transition in Antiferromagnetic SrMnO3 Perovskites

Abstract

We study thermal properties of SrMnO3 starting from analysis of the low-energy electronic structure of the Mn4+ ion in oxygen surroundings. As a start point of the studies, simulations of a SrMnO3 unit cell were performed with using the density functional theory (DFT). The DFT calculations have revealed ionic character of the compound. In the next stage of calculations the Mn4+ ion was treated as an atomic-like strongly-correlated 3d3 system with the 28-fold degenerated ground term 4F. This degeneracy is lifted under the combined action of the dominant octahedral crystal field and the on-site spin-orbit coupling. This study was concentrated on the explanation of the temperature dependence of the specific heat showing a pronounced λ-type peak at TN. We have calculated the d-electron contribution to the specific heat both in the antiferromagnetic and paramagnetic states. We have found that the entropy of the magnetic contribution is close Rln4 - a value expected from the 4A2g ground subterm of the Mn4+ ions. e.g. 11.5 J/Kmol.