The Magnetic Properties of Fe4BO7 and Mn4BO7 Tetraborates in Three Structural Types

A. S. Shinkorenko// JETP Letters//

The crystal structure and magnetic properties of Fe4BO7 and Mn4BO7 tetraborates have been studied within DFT-GGA. The tetraborates can be found in several possible structural modifications. We considered here three of them, namely Pbca (α-ZnB4O7), Cmcm (β-ZnB4O7 structural type) and P6522 (γ-NiB4O7 structural type). The possible magnetic orderings in three structural types are described within group-theoretical analysis. The following DFT calculations allow find the lowest energy magnetic structure for Fe4BO7 and Mn4BO7 in three structural types. The total energy of tetraborates in three structural types was compared with and without taking into account of the spin-polarization. It was found that in non-spin-polarized case Mn4BO7 and Fe4BO7 have α-ZnB4O7 and γ-NiB4O7 structural types as lowest energy structure, correspondingly. However, taking into account magnetic structure results in the anitiferromagnetic α-ZnB4O7 phase appears to be the ground state for both tetraborates. The pressure behavior of enthalpy of Fe4BO7 and Mn4BO7 tetraborates were studied. We obtained that the applied pressure results in the arising of β-ZnB4O7 structural type as the lowest energy structure under pressure.