Spin dynamics of Gd in an applied magnetic field

Abstract

Quasi-elastic and inelastic neutron scattering were used to study the effect of an applied magnetic field on the spin dynamics of Gd at temperatures near Tc. The quasi-elastic critical scattering shows a rapid decrease with applied field which is well reproduced by an RPA model. At these elevated temperatures the spin wave energies are proportional to the magnetisation only at small q. At larger q, they shift upward in accordance with the correlation theory treatment by Lindgard (1984). In both wavevector regions, the spin wave spectra are the same at equivalent magnetisations, regardless of whether that is a spontaneous magnetisation at T<Tc or an induced magnetisation at T>Tc.