Critical behavior, magnetic and magnetocaloric properties of melt-spun Ni50Mn35Sn15 ribbons

Abstract

Microstructure, structural and magnetic phase transitions of the melt spun Ni50Mn35Sn15 ribbons have been examined by means of scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and magnetic measurements. The melt spun ribbons exhibit a single phase cubic L21 austenite structure at room temperature with a space group Fm−3m, and lattice parameter a = 5.956 Å. The DSC results reveal the first order reverse and forward martensitic transition (Ms = 147.4 K, Mf = 133.7 K, As = 155 K and Af = 171 K) with a thermal hysteresis of about 21.3 K around the martensitic transition between heating and cooling. The thermomagnetic measurements show that the melt spun ribbons undergo a second order magnetic transition at a Curie temperature TC = 310 K and a first order martensitic transition at TM = 160 K. The critical behavior associated with the magnetic phase transition has been investigated through the isothermal magnetization measurements around TC. The critical exponents have been estimated by several methods such as the modified Arrott plots, Kouvel-Fisher method and critical isothermal analysis. The critical exponents values β=0.456, γ=0.88 and δ=2.929 are close to those predicted from the mean field model revealing a dominated long-range order of magnetic interactions. For an applied magnetic field of 5 T, the maximum magnetic entropy change (ΔSMmax) and the relative cooling power (RCP) values around TC are of about 2.105 J/kg.K and 132.5 J/kg, respectively. The melt-spun Ni50Mn35Sn15 alloy is a good candidate for magnetic refrigeration near room temperature.