Electronic structure of collinear states in magnetically ordered phases of some alloys of Fe2-xMnxAs system

First-principles calculations using the SPRKKR program package are done to investigate the electronic and magnetic structures of some alloys of the Fe2-xMnxAs system with a tetragonal crystal structure C38 (space group P4/nmm). Different versions of collinear antiferromagnetic (x=1.29) and ferrimagnetic (x=1.29, 1.31, 1.35) structures, in which the magnetic moments of the atoms lie in the basal plane of a tetragonal lattice, are considered. It is shown that in Fe0.71Mn1.29As the lowest energy belongs to an antiferromagnetic structure of the Fe2As type. To determine the possible magnetic structure of the ferrimagnetic phase that is induced in the given alloys by a magnetic field, a study was done for the four possible ferrimagnetic configurations for which the magnetic cell is the same as the crystallographic cell. It is found that for one of them the dependence of the magnetization on the Mn concentration is in qualitative agreement with the experimental data. It is shown that for all the antiferromagnetic and ferrimagnetic configurations studied, the value of the magnetic moments is not noticeably affected by a change of their orientation. Based on a comparison of the results of the calculations with various experimental data, it is concluded that there is a demand for refined neutron-diffraction studies of the Fe2-xMnxAs system in the concentration region 1.29≤1.52