Order-order magnetic phase transitions in itinerant electron magnetics: MnCoSi

With the results of ab initio calculation of MnCoSi electronic structure and the model of spiral state the magnetic field-induced order-order magnetic phase transitions in MnCoSi under pressure to 2 kbar have been analyzed. It follows that the magnetic moments of Mn and Co in MnCoSi are created by itinerant d-electrons and that stimulation of induced order-order phase transitions in this material by pressure may be a consequence of structural changes in density of delectronic states with pressure increase. The induced order-order transitions are described with the singleband spiral state model in which band filling and nonmagnetic density of electronic states are based on the electronic structure calculations from the first principles for MnCoSi. Within the model it is shown that the low-temperature phases induced via magnetic field are non-collinear ferromagnetic structures, and represent the coexistence of homogeneous ferromagnetic and periodic spiral components of the total magnetic moment of d-band. At the low temperatures a pure ferromagnetic state is considered as a metastable one. PACS: 75.30.Kz Magnetic phase boundaries; 75.50.-y Studies of specific magnetic materials.