Spin-Wave Spectrum of Nickel Metal

Abstract

The spin‐wave spectrum of nickel metal has been measured in the three principal symmetry directions by inelastic neutron scattering using the triple‐axis technique. A large crystal of ⁶⁰Ni was used to avoid incoherent scattering and reduce contributions from phonon scattering. The spin‐wave dispersion curve rises quadratically in each of the three directions according to the relation E=Dq² when D is about 430 meV Ų. The spin‐wave intensity decreases slowly with increasing energy and then drops suddenly by more than an order of magnitude. This sudden decrease occurs at different energies for the three symmetry directions and in accordance with calculations is interpreted as the intersection of the spin‐wave dispersion curve with a continuum band of excitations. In the [100] direction this intersection corresponds to an energy of about 100 meV and a q of about 0.4 A⁻¹. These results along with band calculations by Hanus indicate a d band splitting of 0.57 eV. The measured spin‐wave spectra are similar to those calculated with an interatomic exchange of 0.025 eV.