Thermal Stability of Electrodeposited Fe-55wt%Ni Alloy and Effect of Low-Temperature Heat Treatment on Magnetic Properties

Abstract

Electrodeposited nanocrystalline soft magnetic materials have emerged as one of the hottest research topics in the field of magnetic materials due to they are easy to implement in miniaturization, lightweight, and energy-saving of electronic devices. The thermal stability and grain growth process of electrodeposited Fe-55wt%Ni alloy were investigated. Results indicated that the grain growth was rapid at a temperature of about 678 K, while the exothermic peak appeared in DSC with an exothermic heat of about 12 ± 1 J g−1. The activation energy for grain growth was obtained through the optimized Kissinger equation and isothermal kinetics calculations, and the growth mechanism was evaluated based on the calculation results. Below 678 K, the activation energy required for grain growth was low, which implied the growth mechanism was the rearrangement of atoms at the grain boundary; Above 678 K, the growth mechanism was grain boundary diffusion. After the low-temperature heat treatment, the coercivity (H c) decreased and the saturation magnetization (M s) increased slightly, which was attributed to the reduction of internal stress and the ultra-fine nanocrystalline structure. The optimal heat treatment process was 573 K heat treatment for 5 h, where M s and H c of 160 emu g−1 and below 1 Oe, respectively.

Improving the Magnetic Properties of Electrodeposited Fe-55wt%Ni Alloy via Abnormal Grain Growth Induced by Second-Phase Particles

“…The coercivity of the annealed alloy is initially higher than that of the as-deposited film, but it gradually decreases as the annealing temperature increases. The results of our previous study 32 show that the grain size of the electrodeposited Fe-55 wt%Ni alloys is in the nanoscale. When the size of the nanoparticles is less than the ferromagnetic exchange length, the smoothing effect resulting from exchange interactions between nanoparticles counteracts the anisotropy of the local random orientation, leading to a low coercivity.…”