Dispersion Relations for Magnetic Excitons in NdAl2

The magnetic excitation spectrum in NdAl2 has been measured by means of inelastic neutron scattering at 5.3K for momentum transfer in the (110) direction. Several excitation branches are observed and discussed in terms of a hamiltonian including an isotropic Heisenberg exchange interaction and a cubic crystalline electric field.

The spectrum is interpreted as comprising of six excitation modes four of which are transverse spin-wave-like excitations (two acoustic and two optical). The remaining two excitations are longitudinal in character (acoustic and optical). The authors obtain values for both the exchange interaction and the crystal-field parameters.