Magnetic Properties and Microstructure of Nd56Fe30Al10Dy4 Bulk Amorphous Alloy during Crystallization Process

Nd56Fe30Al10Dy4 bulk amorphous alloy was prepared by copper mould casting. The magnetic properties and microstructure of the alloy during crystallization process were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and scanning electron microscope (SEM). Results indicate that the as-cast alloy exhibits hard magnetic behavior. A few crystalline phases are observed and the intrinsic coercivity and saturation magnetization of the alloy decrease slightly after annealing at 765 K. With increasing the annealing temperature, the volume fractions of crystalline phase increase and the volume fractions of amorphous phase decrease gradually in the alloy, while the saturation magnetization of the alloy decrease gradually. It is worthy of noting that intrinsic coercivity changes slightly with increasing the annealing temperature. After annealing at 810 K, the alloy shows paramagnetic behavior while no amorphous alloy is observed. Based on the results of magnetic properties, microstructure and exchange-coupling interaction, it is found that coercivity of the alloy is derived from amorphous phase while it does not depend on the volume fraction. The mechanism responsible for coercivity in Nd-based bulk amorphous alloys could be explained by a strong pinning model.