Effect of severe plastic deformation and magnetic field-assisted heat treatment on the magnetic properties of equiatomic FeNi alloy

This study highlights the effect of high-pressure torsion (HPT), a severe plastic deformation technique, on the magnetic properties of equiatomic FeNi alloys prepared from mechanical alloying. The prime objective of this study is to increase the interdiffusion of FeNi and accelerate the formation of L1₀ ordering. HPT processing on FeNi alloy was carried out at room temperature under 6 GPa for 5, 10 and 20 turns. Subsequently, the samples were subjected to heat treatment in a vacuum at 593 K for 1000 h without any magnetic field. Further heat treatment of 4 h was also performed at 593 K in the presence of a 1.5 T magnetic field. It is observed that HPT processing first increases the lattice strain; however, further processing causes strain relaxation due to dynamic recrystallization. Initially, for 5 turns of HPT, the saturation magnetization decreases. However, after 10 and 20 turns of HPT, the saturation magnetization increases due to recrystallization and formation of L1₀ ordering. After 5 turns, the coercivity increases by ~175% due to lattice strain. With further processing, the coercivity decreases by ~50% due to recrystallization. Heat treatment on the HPT-processed samples shows increased coercivity and remanence due to the annihilation of defects and formation of short-range L1₀ ordering.