Short wavelength magnetic excitations in random ferromagnets

Abstract

Neutron inelastic scattering measurements on a single crystal sample of random chromium-iron alloy with 27% iron have been made in the ferromagnetic phase. The percolation composition in this system is 19% iron, so that the effects of the chemical, and hence magnetic disorder, on the magnetic excitation spectrum are expected to be large. Broad distributions centred on zero energy are observed over much of the Brillouin zone, with the exception of a small region near the zone centre ( q < 0.1 Å -1 ) where well-defined inelastic scattering (propagating spin wave mode) is seen. The results are compared with computer experiments on a nearest-neighbour dilute Heisenberg ferromagnet model, for which an equation-of-motion technique was used to generate the excitation spectrum. The comparison reveals the dominant effects on the excitations are from the disorder. Effects due to the Stoner excitations are not observed.