Magnetic Properties of Amorphous Fe-Nd Alloys*

Melt-spun amorphous Fe 1- x Nd 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 57 Fe at 77 K is independent of x and about 300 kOe on an average, suggesting that the magnetic moment of Fe is about 2.0 µ 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 Nd 3+ . 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.