Magnetostructural features of phase transitions in the Mn-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-NiGe system Part 2. Analysis

Within the framework of the model of interacting parameters of the magnetic and structural orders, taking into account the internal periodic magnetic field orthogonal to the exchange field, we analyzed the features of magnetostructural transitions in the Mn1-xCoxNiGe system. A qualitative description of changes in the nature of magnetic phase transitions from magnetostructural transitions of the 1st order paramagnetism-antiferromagnetism (x=0.05-0.1) to isostructural transitions of the 2nd order paramagnetism-ferromagnetism (x=0.15-0.8) with a change in the concentration of Co is presented. An explanation is given for the onset of irreversible magnetic-field-induced transitions at temperatures on the order of 5 K in strong magnetic fields, accompanied by a change in the saturation magnetization for samples x=0.15-0.8. The low-temperature inverse magnetocaloric effect at liquid helium temperatures is predicted for these samples. Keywords: irreversible magnetostructural first-order phase transition, helimagnetism, direct and inverse magnetocaloric effects. </jats:p

Magnetostructural features of phase transitions in the Mn-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-NiGe system Part 1. Experimental results

Experimental studies of the magnetic and structural properties of solid solutions of the Mn1-xCoxNiGe system in a wide range of Co concentrations (0.05≤ x≤ 0.8), temperatures (5 K≤ x≤600 K) and magnetic fields (0.016 T≤ x≤ 13.5 T) have revealed a number of nontrivial magnetic and magnetocaloric features of this system. The latter include: 1) a change in the nature of magnetic phase transitions from magnetostructural transitions of the 1st order paramagnetism-antiferromagnetism (0.05≤ x≤ 0.15) to isostructural transitions of the 2nd order paramagnetism-ferromagnetism (0.15≤ x≤0.8) with a change in the concentration of Co ; 2) anomalous behavior of low-temperature regions of magnetization in weak magnetic fields; 3) a change in the saturation magnetization and the appearance of irreversible magnetic field-induced transitions at helium temperatures in strong magnetic fields. Keywords: irreversible magnetostructural first-order phase transition, helimagnetism, direct and inverse magnetocaloric effects. </jats:p