Magnetism and the low-energy electronic structure of Mott insulators K2CoF4 and SrMnO3 perovskites

•The octahedral crystal-field 10Dq amounts to 0.98 and 2.25 eV in K2CoF4 and SrMnO3.•The low-energy electronic structures in the magnetic state is displayed.•There is a strong interplay of the magnetism and the local crystal structure.•Temperature dependence of the Mn4+- ion magnetic moment has been described.•Relativistic spin-orbit coupling is indispensable for description of 3d magnetism.

For Mott insulators, K2CoF4 and SrMnO3, we have calculated, in the purely ionic model, the low-energy electronic structure both in the paramagnetic and magnetic state as well as zero-temperature magnetic moment, its direction and its temperature dependence. We have calculated the octahedral crystal-field strength 10Dq to be 0.98 and 2.25 eV. We claim that for an adequate theoretical description of magnetic properties even small local distortions and the intra-atomic relativistic spin-orbit coupling have to be taken into account. Our studies have revealed a strong interplay of the magnetism, the orbital moment in particular, with the local crystallographic structure. The calculated orbital moment in K2CoF4 is very large, 1.06 μB, giving 30% contribution to the total moment - this result points the necessity to “unquench” the orbital magnetism in 3d compounds. We consistently described magnetic and some optical properties of these compounds, containing atoms with incomplete 3d shell, in agreement with their insulating ground state.