Magnetic excitations in TmCu

The magnetic excitations have been studied in the rare-earth intermetallic compound TmCu by means of inelastic neutron scattering. Dispersion curves have been followed through the cubic Brillouin zone, in particular an intense and dispersive transverse branch: this latter presents a lifting of the degeneracy along particular directions. Within a generalized susceptibility formalism, this is related to the coupling of the excitations at q and q + Q, where Q = (π/a, π/a, 0) is the antiferromagn etic propagation vector in TmCu. The inter-ionic isotropic bilinear exchange parameters are deduced and compared with those of isomorphous compounds.