Neutron-scattering study of the magnetic excitations of thulium metal

We have performed neutron-scattering experiments to study the magnetic excitations of Tm in its low-temperature ferrimagnetic-antiphase-domain (FAD) phase. Our measurements confirm our earlier finding that the excitation spectrum of Tm in its FAD phase consists of one magnon mode with limited dispersion (8.3"9.6 meV). This result suggests that the Hamiltonian is dominated by the crystal-field-anisotropy energy and that the exchange interaction is relatively weak. Two additional lower-energy excitations have also been observed, and they have been identified as originating from magnetovibrational scattering from the TA phonon.