Thermal behaviour and magnetic properties of B-rich NdFeB nanocomposite hard magnetic alloys with partial substitution of Dy for Nd

Abstract

B-rich NdFeB base alloys with partial substitutions of Dy for Nd ((Nd1-xDyx)4.5Fe77B18.5 (x = 0-0.4)) were chosen to study the influence of Dy on thermal behaviour and magnetic properties. It was found that partial substitution of Dy for Nd results in a dramatic enhancement of coercivity jHc from 183 to 261 kA m-1 and of maximum magnetic product (BH)max from 110.6 to 133.7 kJ m-3. However, the saturation magnetization Ms only decreases about 22.8 kA m-1 for every 0.1 increment of Dy content x. Differential thermal analysis traces show that the crystallization process of the initial amorphous ribbons is a three-peak process. X-ray diffraction and differential thermal analysis indicate that the three peaks correspond to the formation of crystalline Fe3B, Nd2Fe14B, and α-Fe, respectively. With increase of Dy concentration, jHc increases to a maximum value at about x = 0.1, and then reduces gradually. The enhancement of coercivity arises from the increase of the anisotropy field for the hard magnetic phase. The reduction of intrinsic coercivity jHc is attributed to the emergence of α-Fe after annealing at the third peak and the reduction of the fraction of hard magnetic phase due to the Dy addition. In order to obtain the optimum magnetic properties, a special annealing method was used.