Spin-wave excitations in amorphous Fe78B13Si9

Inelastic neutron scattering measurements have been used to study the long wavelength spin dynamics of the high T/sub c/ amorphous ferromagnetic alloy Fe78B13Si9 (Metglas 2605S2). Spin waves were observed over the accessible wave-vector range of 0.06 A-1≤q≤0.12 A-1, for temperatures between 473 K (0.67 T/sub c/) and 705 K (0.99 T/sub c/). The magnon dispersion curves exhibit the conventional quadratic relationship E = D(T)q2+Δ, typical of an isotropic ferromagnet, where the small energy gap Δ≅0.05 meV is attributed primarily to the dipole-dipole interaction. An estimate of the T = 0 value of D≅156 meV A2 was obtained from a plot of D(T) vs T extrapolated to low temperatures, while the Curie temperature of 710 K was obtained from the extrapolation of D(T) to zero at high temperatures. Spin-wave linewidth data for T/T/sub c/≅0.95 showed the q4 wave-vector dependence expected for magnon-magnon interactions