Magnetic Properties of Amorphous Fe-Nd Alloys

Melt-spun amorphous Fe_1-xNd_x alloys (0.11≦x≦0.60) were investigated by the magnetization measurement up to 143 kOe and the Mössbauer spectroscopy. The coercive field at 4.2 K increases abruptly at around x=0.30 with increasing x, amounting to 53 kOe at x=0.40. The hyperfine field of ⁵⁷Fe at 77 K is independent of x and about 300 kOe on an average, suggesting that the magnetic moment of Fe is about 2.0μ_B/atom throughout this system. On this assumption and the measured magnetization at 4.2 K, it is estimated that the average Nd moment is about 3.2 μ_B/atom at the low x limit. This value corresponds to the free ion value of Nd³⁺. The Nd moment decreases with increasing x to one half, 1.6 μ_B/atom. A ferromagnetic cluster model with large random anisotropy is proposed for the high coercivity alloys of this system. Magnetization curves at 4.2 K are well explained by the model, by an adjustment of the parameters for the anisotropy energy of the cluster and the inter-cluster coupling. The concentration dependence of the coercive field is discussed briefly.