Abstract:
The results of experimental studies of magnetic and magnetocaloric properties of quenched Mn$_{0.89}$Cr$_{0.11}$NiGe samples are presented. It is shown that magnetic phase transitions from the paramagnetic to the helical state become diffuse magnetostructural phase transitions of the first order PMhex$(P6_3/mmc)$$\leftrightarrow$ HMorth$(Pnma)$, which is the reason for the multiple enhancement of magnetocaloric properties compared to the unquenched sample. An additional feature of quenching is the possibility of decreasing the magnetostructural transition temperature for samples with minor deviations in quenching protocols. A theoretical analysis of the merging of the diffuse first-order structural transition PMhex$(P6_3/mmc)$$\leftrightarrow$ PMorth$(Pnma)$ and the second-order magnetic isostructural transition PMorth$(Pnma)$–HMorth$(Pnma)$ into a single first-order magnetostructural transition PMhex$(P6_3/mmc)$$\leftrightarrow$ HMorth$(Pnma)$ during quenching of Mn$_{0.89}$Cr$_{0.11}$NiGe is carried out. Within the framework of the model of cooperative local displacements of Ge and Ni atoms and the concept of diffuse first-order phase transitions, a theoretical description of magnetostructural transitions in slowly cooled and quenched Mn$_{0.89}$Cr$_{0.11}$NiGe alloy is proposed.
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