Giant Room-Temperature Magnetocaloric Effect Across the Magnetostructural Transition in (MnNiSi)1−x(FeCoGa)x Alloys

Abstract

Magnetic and structural transitions are observed to coincide at around room temperature in transition-metal-based $(\mathrm{Mn}\mathrm{Ni}\mathrm{Si}{)}_{1\text{\ensuremath{-}}x}(\mathrm{Fe}\mathrm{Co}\mathrm{Ga}{)}_{x}$ (x = 0.15 and 0.16) alloys, which leads to a coupled first-order magnetostructural transition (MST) from paramagnetic hexagonal to ferromagnetic orthorhombic structure, and, as a result, a giant magnetocaloric effect is observed in these alloys. With subsequent doping for x = 0.17, the MST decouples into two separate transitions, structural and magnetic, although the transitions couple upon enhancing the applied magnetic field. The alloys with x = 0.15, 0.16, and 0.17 are found to exhibit isothermal magnetic entropy changes ($|\mathrm{\ensuremath{\Delta}}{S}_{M}|$) as large as about $25\phantom{\rule{0.1em}{0ex}}\mathrm{J}\phantom{\rule{0.1em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 323 K, about $31.1\phantom{\rule{0.1em}{0ex}}\mathrm{J}\phantom{\rule{0.1em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 281 K, and about $23.8\phantom{\rule{0.1em}{0ex}}\mathrm{J}\phantom{\rule{0.1em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{0.1em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 213 K, respectively, due to a field change of \ensuremath{\Delta}H = 50 kOe. These low-cost materials may be considered as promising candidates for magnetic refrigeration around room temperature due to their giant magnetocaloric properties, with significantly large relative cooling power (RCP = 191.8, 209.6, and 139.2 J/kg, respectively, for x = 0.15, 0.16, and 0.17 due to \ensuremath{\Delta}H = 50 kOe).