Subjugating extensive magnetostructural temperature window and giant magnetocaloric effect in B-doped (MnNiSi)0.67(Fe2Ge)0.33 hexagonal system

Abstract

Coupled first-order magnetostructural transformations (FOMSTs) with narrow widths governed by low external stimuli play a crucial role in magnetic refrigeration for ferromagnetic hexagonal systems. In this work, we report a family of magnetocaloric materials named boron (B)-doped ${\left(\mathrm{MnNiSi}\right)}_{0.67}{\left(\mathrm{F}{\mathrm{e}}_2\mathrm{Ge}\right)}_{0.33}$ compounds that are devoid of rare-earth elements. Our results show that varying B concentrations up to 5 at. % can tailor the robust FOMSTs between the low-temperature ferromagnetic orthorhombic phase and the high-temperature paramagnetic hexagonal phase in a wider temperature regime. A dramatic change in hysteresis ($\mathrm{\Delta }{T}_{\mathrm{hys}}$) from ∼25 K for $x=0$ to ∼8 (9) K as well as increases in the saturation magnetization for specific 2 (3) at. % of B dopants is pronounced. Henceforth, the origin of the reducing hysteresis is illustrated based on the geometrical compatibility conditions $({\lambda }_2\sim 1)$ between the austenite and martensite phases using temperature-dependent powder x-ray diffraction analysis. Moreover, we found the samples performed with good functional stability from the thermal cycling run. The branch of these B doping materials exhibits robust features of a large magnetocaloric effect (MCE) over an extensive temperature range (∼71 K) and temperature-averaged magnetic entropy change at a lower magnetic field change of 2 T. These several tangible benefits, such as reduced $\mathrm{\Delta }{T}_{\mathrm{hys}}$, geometrical compatibility, and robust MCE properties are first reported in the studied hexagonal system. Therefore, our results offer a viable approach to improve the cascading of these materials towards the application of cooling technology.