Magnetic properties of amorphous neodymium–transition-metal films

Abstract

Amorphous thin films of NdxCo1−x and NdxFe1−x alloys were prepared over the compositional range 0.08⩽x⩽0.71 by e-beam evaporation. Magnetization and anisotropy of the samples were studied over a wide temperature range with the aid of a force balance magnetometer, Hall effect measurements, and Mössbauer spectroscopy. It was found that the magnetization of the alloys could not be accounted for by a completely collinear alignment (ferromagnetic) of the Nd and transition-metal subnetworks. Mean field analysis of the magnetization data showed a large reduction of the Nd–transition-metal exchange coupling as compared to their Gd analogs. A model was developed which requires that Nd be dispersed in a cone whose axis is parallel to that of the transition-metal subnetwork by strong coupling to randomly oriented local crystal field axes. This dispersion reduces the Nd net moment to 77% of its free-ion moment in NdxCo1−x alloys and to 25% of its free-ion moment in NdxFe1−x alloys. There is evidence that some dispersion also occurs in the Fe subnetwork. Anisotropy in NdxCo1−x alloys was found to be proportional to the square of the Nd subnetwork magnetization, Ku=CM2Nd. C was exponentially dependent on concentration according to the relation C=6 exp(−10x).