NiMnSn half Heusler alloy: Critical phenomena at the ferromagnetic to paramagnetic phase transition

Abstract

The critical magnetic analysis and magnetocaloric effect of NiMnSn half Heusler alloy have been explored in this article. This alloy undergoes ferromagnetic to paramagnetic second order phase transition above room temperature at around 388 K. To understand the exchange interaction, magnetic ordering and magnetic phase transition, the critical magnetic analysis has been carried out around the transition temperature. Critical exponents are turned out to be β = 0.44, γ = 1.1 and δ = 3.1. These values imply that the exchange interaction is following towards mean field theory i.e., long-range magnetic ordering is present in the system. The absence of one Ni atom from full Heusler Ni2MnSn alloy does not affect much the magnetic ordering of half Heusler NiMnSn. For environment-friendly solid state cooling applications, the magnetocaloric effect of NiMnSn has been studied. The magnetic entropy change is calculated to be high as 0.81 J/kg-K near the transition temperature for a moderate field change of 30 kOe.