CRYSTAL-FIELD EXCITATIONS AND MAGNETIC-PROPERTIES OF TMPO4

The magnetic-excitation spectrum of TmPO4 has been studied using inelastic neutron scattering techniques. Sharp crystal-field transitions were observed in spectra obtained at 15 and 100 K, yielding new information regarding the energy-level structure of the Tm3+ ground-multiplet splitting. The data were analyzed using a Hamiltonian that included the atomic free-ion and crystal-field interactions for an f12 Configuration. Using the Tm free-ion parameters derived from optical spectroscopy of Tm3+ diluted in a LuPO4 host, a set of crystal-field parameters were obtained for Tm3+ in pure TmPO4. The calculated magnetic spectra of TmPO4 agree very well with the results of neutron and Raman measurements. The calculated bulk magnetic susceptibility of TmPO4 exhibits a large anisotropy at low temperature and is in good agreement with the experimental data. A significant contribution to the specific heat from the Tm3+ crystal-field states was found at temperatures below 100 K.