Optimization of magnetic domain structure and soft magnetic properties of FeCoNiGd medium-entropy alloys by gadolinium addition

Soft magnetic high-entropy alloys (HEAs) have attracted much attention due to their excellent mechanical properties and high electrical resistivity. However, the magnetic dilution caused by non-magnetic elements in HEAs greatly reduces their saturation magnetization (Ms). In this work, FeCoNiGdx medium-entropy alloys (MEAs) were prepared by adding gadolinium, a rare earth element with ferromagnetism near room temperature, into FeCoNi alloy to study its influence on the microstructure and magnetic properties. The results demonstrate that the addition of Gd can promote the precipitation of intermetallic compound phases in FeCoNi alloy. When x decreases from 1 to 0.5, the intermetallic compound phases change from GdM2 (M=Fe, Co, Ni) phase to GdM5 phase, and it becomes Gd2M17 phase if x <= 0.07. Moreover, the addition of a minor amount of Gd significantly optimizes the remanence (Br), while slightly worsens the saturation magnetization (Ms) and coercivity (Hc). Finally, the FeCoNiGd0.03 MEA achieves the best comprehensive magnetic properties with high Ms= 149.58 emu/g, low Hc= 434.3 A/m and Br= 0.231 mT owing to the high content of ferromagnetic elements and reasonable distribution of the magnetic domain structure. This work can provide insights into the role of rare earth elements on microstructure and magnetic properties of MEAs and HEAs.