Golovchan O. Interrelation between electronic, magnetic and crystal structures in iron-manganese pnictides

The thesis is devoted to a systematic study of the electronic structure of iron-manganese pnictides using density functional theory methods. It is shown that a change of symmetry of the MnAs crystal lattice at the occurrence of ferromagnetism is caused by competition of magnetic and structural order parameters. Systematic investigation of the effect of anionic and cationic substitutions on the electronic structure and local magnetic moments of hexagonal MnAs is performed. Recommendations relating the choice of optimal substitutions (from the viewpoint of magnetocaloric applications) are offered. Comparison of the electronic structure data for the Mn2-xFexAsyP1-y system with experimental data has allowed to predict and to find out experimentally the existence of a triple point on the temperature-concentration phase diagram. A concept of mixed magnetic states which consistently explains behavior of the alloys in a magnetic field is proposed and grounded.