CRYSTAL-FIELD EXCITATIONS AND MAGNETIC-PROPERTIES OF HO3+ IN HOVO4

The magnetic excitations in HoVO4 were studied by neutron scattering and susceptibility techniques. Well-defined transitions between the crystal-field-split states of the Ho3+ ions were observed at 15, 40, and 100 K. The magnetic spectra were analyzed using a single-ion crystal-field model which includes intermediate coupling of the LS states of Ho. A quantitative comparison of the observed energies and intensities with the model was made and used to refine the five crystal-field parameters needed to calculate the Ho ionic wave functions and other magnetic properties. The nonmagnetic Γ1-singlet ground state (containing about 90% pure 8,0 component) of the Ho ions, in conjunction with the next higher doublet state situated at 2.5 meV, strongly influences the low-temperature magnetic behavior. The calculated magnetic susceptibility, which exhibits an easy plane coinciding with the crystallographic a-b plane at low temperatures, agrees very well with the experimental data obtained from single-crystal measurements. The magnetic properties of HoVO4 are contrasted with those of an isostructural compound HoPO4 which has a 98% pure 8,7-doublet ground state. The difference in the crystal-field-level structure between these two compounds is reflected in a sign change of the B02 crystal-field parameter. Despite the overall tetragonal crystal structure of HoVO4, which predicts double degeneracy for each Γ5 state, a small splitting in the first-excited doublet was clearly observed at low temperatures. © 1995 The American Physical Society.