GROUND-STATE WAVE-FUNCTIONS OF TB3- A NEUTRON-SCATTERING STUDY( IONS IN PARAMAGNETIC TBPO4 )

The paramagnetic-excitation spectrum of TbPO4 has been investigated by means of inelastic neutron-scattering techniques, and the observed cr ystal-field transitions were analyzed using a Hamiltonian that include d the atomic free-ion and crystal-field interactions for an f8 configu ration. Five parameters for the crystal-field potential were obtained that provided a satisfactory description of the neutron data collected at temperatures between 4.2 and 150 K. The calculated crystal-field c ontribution to the specific heat in the 4-10 K temperature range and t he paramagnetic susceptibility agree well with the experimental result s. The large anisotropy of the magnetic ground-state doublet of the Tb ions with respect to the crystallographic c axis has important conseq uences for the spin structure in the antiferromagnetic phases at low t emperatures. The effective internal magnetic field in antiferromagneti c TbPO4 was estimated based on the crystal-field-level scheme and a mo lecular-field approximation and was found to be in good agreement with the values reported from other measurements.