Microstructural and magnetic properties of cobalt-substituted Nd32.5Dy1.0Fe64.2-xCoxNb1.0Al0.2B1.1 alloy prepared by ball milling technique

Nanocrystalline Nd32.5Dy1.0Fe64.2-xCoxNb1.0Al0.2B1.1 (x ​= ​0, 0.5, 1, 1.5, 2.0, & 2.5 ​wt %) alloys were prepared using arc melting method under argon atmosphere followed by ball milling. Results revealed that substitution of 2.0 ​wt% Co for Iron (Fe) is beneficial for excellent microstructure and magnetic properties in the series of studied alloys. Powder ball milling for 80 ​min provokes optimum magnetic properties such as saturation magnetization (Ms) of 71.11 emu/g, remanence magnetization (Mr) of 45.5 emu/g and coercivity (Hc) of 2.87 ​kOe. The Mr/Ms ratio for optimal magnetic powder was determined to be 0.63, which leads to a magnetic exchange coupling between the α-Fe soft and NdFeB hard grains. Magnetic analysis revealed substitution of Co above 2.0 ​wt% for Fe led to the drastic decline of both Ms and Mr due to non-ideal intermetallic phases in the microstructure. Results showed that optimization of parameters at the initial stage (casting and ball milling) is essential to obtain good, hard magnetic properties in the studied alloys.