Enhanced magnetocaloric effect in Fe-rich (NixFe1-x)70.5B17.7Si7.8Ti4 (x = 0.3 and 0.4) mechanically alloyed nanocrystalline powder

Abstract We report the evolution of nanocrystalline α-Fe and γ-Ni phases in (NixFe1-x)70.5B17.7Si7.8Ti4 (at.%) where, x = 0.3 and 0.4, upon mechanical alloying of elemental powder mixtures up to 36 h. The effect of milling time on the nanostructure evolution, thermal stability, and magnetic properties have been investigated throughly using x-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometry (VSM). XRD analysis of the as-milled powders revealed that the lattice parameter and the crystallite size of α-Fe phase lies in between 0.2850-0.2972 nm and 3–14 nm; whereas the same for γ-Ni lies in between 0.3550-0.3608 nm and 8–41 nm, respectively, during milling. The thermal analysis of the as-milled powders suggests that the onset temperature of crystallization increases as Fe content decreases. The thermomagnetic measurement of the heat treated powders has revealed the TC of α-Fe phase in x = 0.3 to be 590 K and that of γ-Ni phase in x = 0.4 to be 375 K. The maximum magnetic entropy change has been estimated to be 0.159 Jkg-1K−1 in x = 0.3, while that of x = 0.4 has been found to be 0.695 Jkg-1K−1 at an applied magnetic field of 19.9 kOe.