Spin-wave excitations and low-temperature magnetization in the amorphous metallic ferromagnetic(FexNi1−x)75P16B6Al3

Abstract

We have carried out a systematic study of the spin-wave dispersion relations and the low-temperature magnetization in the amorphous metallic ferromagnets ${({\mathrm{Fe}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x})}_{75}{\mathrm{P}}_{16}{\mathrm{B}}_{6}{\mathrm{Al}}_{3}$ for $x=1.0, 0.65, 0.5, \mathrm{and} 0.30$. In this series the Ni is, to a first approximation, nonmagnetic. The spin-wave measurements were carried out using inelastic neutron scattering techniques, the magnetization at finite fields (1.2 and 15 kOe) was measured via a vibrating sample magnetometer and the temperature dependence of the magnetization at zero field was deduced from the hyperfine field at the Fe sites as measured by M\ossbauer techniques. The spin waves follow a normal ferromagnetic dispersion relation, $\ensuremath{\hbar}\ensuremath{\omega}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})=\ensuremath{\Delta}+D{q}^{2}+E{q}^{4}+\ensuremath{\cdots}$, in all materials. The magnetization follows the law $M(T)={M}_{o}(1\ensuremath{-}B{T}^{\frac{3}{2}}\ensuremath{-}\ensuremath{\cdots})$. The ${T}^{\frac{3}{2}}$ coefficient $B$ is nearly field independent for the samples with $x=1.0, 0.65, \mathrm{and} 0.5$. Further the M\ossbauer and magnetometer measurements are in close quantitative agreement. We find that for these samples the observed $B'\mathrm{s}$ are properly accounted for by the measured spin-wave dispersion relations in contrast to previous studies in other magnetic glasses. Anomalous effects are observed in the $x=0.30$ sample.