Formation of magnetic phase diagrams in the Mn$_{1-x}$Сr$_x$NiGe system with temperature-separated structural and magnetic phase transitions

The analysis and modeling of magnetostructural diagrams of the Mn$_{1-x}$Сr$_x$NiGe system using an exchange-structural model of interacting parameters of spin and structural orders is carried out. The spin subsystem with a helimagnetic order in the rhombic phase is described in the mean field approximation, and the change in the symmetry of the structural subsystem is taken into account in the approximation of a displaced harmonic oscillator. A qualitative agreement was obtained between the theoretical and experimental features of magnetostructural diagrams under pressure up to 14 kbar.