Effect of rapid quenching on the magnetism and magnetocaloric effect of equiatomic rare earth intermetallic compounds RNi (R = Gd, Tb and Ho)

Magnetocaloric effect (MCE) in RNi (where R = Gd, Tb and Ho) compounds has been studied in their arc-melted and melt-spun forms. The compound GdNi has the orthorhombic CrB-type structure (Space group Cmcm, No. 63) and the compound HoNi has the orthorhombic FeB-type structure (Space group Pnma, No. 62) at room temperature regardless of their synthesis condition. However, arc-melted TbNi orders in a monoclinic structure (Space group P2(1)/m, No. 11) and when it is rapidly quenched to a melt-spun form, it crystallizes in an orthorhombic structure (Space group Pnma, No. 62). The arc-melted GdNi, TbNi and HoNi compounds order ferromagnetically at similar to 69 K, similar to 67 K and similar to 36 K (T-C) respectively. While the melt-spun GdNi shows about 6 K increase in T-C, the ordering temperature of TbNi remains nearly the same in both arc-melted and melt-spun forms. In contrast, a reduction in T-C by about 8 K is observed in melt-spun HoNi, when compared to its arc-melted counterpart. Isothermal magnetic entropy change,Delta S-m, calculated from the field dependent magnetization data indicates an enhanced relative cooling power (RCP) for melt-spun GdNi for field changes of 20 kOe and 50 kOe. A lowered RCP value is observed in melt-spun TbNi and HoNi. These changes could have resulted from the competing shape anisotropy and the granular microstructure induced by the melt-spinning process. Tailoring the MCE of rare earth inter-metallic compounds by suitably controlled synthesis techniques is certainly one of the directions to go forward in the search of giant magnetocaloric materials. (C) 2017 Elsevier B.V. All rights reserved.