Structure and magnetic properties of nanostructured Ni_0.77Fe_0.16Cu_0.05Cr_0.02 (Mumetal) powders prepared by mechanical alloying

Ni-Fe based alloy powders are interesting materials for their application as soft magnetic material with low coercivity and high permeability. In this study, nanocrystalline Ni_0.77Fe_0.16Cu_0.05Cr_0.02 (Mumetal) alloy powders were synthesized by mechanical alloying process using planetary high-energy ball mill under argon atmosphere. The alloy formation and different physical properties were studied as a function of milling time (h), ranging from 0 h to 96 h, using X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and the vibrating sample magnetometer (VSM). The complete phase formation of γ-(Fe, Ni, Cu, Cr) is observed after 12 h milling time. Powder morphology at different stages was examined by SEM and different particle shape was observed. Saturation magnetization and coercivity derived from the hysteresis curves are discussed as a function of milling time and showed that saturation magnetization increases and coercivity decreases with milling time. Increase in milling time, led to reduction in crystallite size 〈D〉 and increase in lattice parameter 〈a〉, thus inducing a higher magnetization and lower coercitivity.