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

Magnetic and structural transitions are observed to coincide at around room temperature in transition-metal-based (MnNiSi)(1-x)(FeCoGa)(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 (vertical bar Delta S-M vertical bar) as large as about 25 J kg(-1) K-1 at 323 K, about 31.1 J kg(-1) K-1 at 281 K, and about 23.8 J kg(-1) K-1 at 213 K, respectively, due to a field change of 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 Delta H = 50 kOe).