Magnetic excitations in amorphous Fe75P15C10

Abstract

Neutron scattering techniques have been used to measure the magnetic excitations in the amorphous ferromagnet ${\mathrm{Fe}}_{75}$ ${\mathrm{P}}_{15}$ ${\mathrm{C}}_{10}$. Triple-axis measurements show a distinct spin-wave excitation at small momentum transfers that closely obeys a quadratic dispersion relation $E=D{Q}^2$ for $D$ equal to about 120 meV ${\mathrm{\AA }}^2$. Time-of-flight polarized-beam measurements made in the vicinity of the first peak in $S\left(Q\right)\mathrm{}$ near 3 ${\mathrm{\AA }}^{-1\mathrm{}}$ show excitations that reach a minimum energy at the maximum in $S\left(Q\right)\mathrm{}$. These excitations are similar to the roton excitations in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ except that they are rather broad in energy since they are able to decay into single-particle states. A contour map is presented which shows the scattering measurements in the neighborhood of 3 ${\mathrm{\AA }}^{-1\mathrm{}}$ and the results are compared with calculations of magnetic excitations in amorphous systems.