Temperature-baric features of magnetic characteristics in systems with structural transitions of the displacement type

Abstract

Using pnictides MnAs and germaindes Mn0.89Cr0.11NiGe as an example, the transformation of thermobaric features of their magnetic characteristics at high pressures is considered. A unified approach is used to describe paramagnetic (PM) structural transitions of the displacement type with a change in the symmetry PM(P6_3/mmc)-PM(Pnma) from hexagonal to orthorhombic. It is shown that the competition between the parameters of the structural and magnetic orders in both systems manifests itself differently in the stabilization and alternation of the so-called high-spin and low-spin magnetically ordered states initiated by pressure. As a consequence, the structural contribution in these systems weakens (MnAs) or enhances Mn0.89Cr0.11NiGe the giant magnetocaloric effect in the temperature-baric region of the first-order magnetostructural phase transitions. Keywords: structural phase transitions of the displacement type, magnetostructural phase transitions, helimagnetism, ferromagnetism, high spin-low spin states, direct magnetocaloric effect.