Magnetic Excitations in the Amorphous FerromagnetCo4P

Abstract

Magnetic excitations in the amorphous ferromagnet ${\mathrm{Co}}_4$P have been studied by use of neutron-inelastic-scattering techniques. Measurements around $Q=0\mathrm{}$ show distinct spin-wave excitations that obey a quadratic dispersion law $E=D{Q}^2$ where $D=185\mathrm{}$ meV ${\mathrm{\AA }}^2$. Additional measurements around the first peak in the static structure factor $S\left(Q\right)\mathrm{}$ show magnetic excitations that appear analogous to the roton excitations in ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. These excitations are discussed in terms of sum rules for the magnetic scattering.