Sweep-Rate Dependence of the Large Magnetocaloric Effect across the Magnetostructural Transition in the Mn0.6Fe0.4(Ni,Co)Si System

Abstract

A coupled magnetostructural transition (MST) from a high-temperature low-magnetic ${\mathrm{Ni}}_{2}\mathrm{In}$-type hexagonal phase to a low-temperature high-magnetic $\mathrm{Ti}\mathrm{Ni}\mathrm{Si}$-type orthorhombic phase, and the associated large magnetocaloric effect, are explored for the $({\mathrm{Mn}}_{0.6}{\mathrm{Fe}}_{0.4})({\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x})\mathrm{Si}$ system. Room-temperature structural analysis is carried out to investigate the orthorhombic distortion of the hexagonal phase initiated by introducing $\mathrm{Co}$ at the $\mathrm{Ni}$ site. The indirect isothermal magnetic measurement technique is employed to estimate the magnetocaloric effect across the coupled phase transition. Fascinatingly, a relatively large value of isothermal magnetic entropy change (\ensuremath{\Delta}$S_{M}$) of (\ensuremath{-}12.02 \ifmmode\pm\else\textpm\fi{} 0.34) J ${\rm{kg}}^{-1}\;{\rm{K}}^{-1}$ at (332.5 \ifmmode\pm\else\textpm\fi{} 0.2) K and relative cooling power (RCP) of (119.6 \ifmmode\pm\else\textpm\fi{} 3.5) J ${\rm{kg}}^{-1}$ is achieved for the composition $({\mathrm{Mn}}_{0.6}{\mathrm{Fe}}_{0.4})({\mathrm{Ni}}_{0.6}{\mathrm{Co}}_{0.4})\mathrm{Si}$, for a field change of 30 kOe. The complex hysteresis behavior around the phase transition determines the efficiency of the material, which is revealed by both temperature- and field-sweep-rate dependence magnetization studies. Superheating (or supercooling) of the parent phase observed at higher temperature and field-sweep rates leads to broad thermal- and field-induced hysteresis. Lower sweep rates of temperature and magnetic field remove the quenching phenomenon across the MST and enhance the working efficiency. A large magnetocaloric effect and negligible variation of hysteresis with the temperature- and magnetic-field-sweep rates compared with other alloys makes this nominal low-cost material a promising candidate for practical solid-state cooling applications.