Crystal-field excitations and magnetic properties of Ho3+ in HoVO4.

Abstract

The magnetic excitations in ${\mathrm{HoVO}}_{4}$ were studied by neutron scattering and susceptibility techniques. Well-defined transitions between the crystal-field-split states of the ${\mathrm{Ho}}^{3+}$ 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 ${\mathrm{\ensuremath{\Gamma}}}_{1}$-singlet ground state (containing about 90% pure \ensuremath{\Vert}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 ${\mathrm{HoVO}}_{4}$ are contrasted with those of an isostructural compound ${\mathrm{HoPO}}_{4}$ which has a 98% pure \ensuremath{\Vert}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 ${\mathit{B}}_{0}^{2}$ crystal-field parameter. Despite the overall tetragonal crystal structure of ${\mathrm{HoVO}}_{4}$, which predicts double degeneracy for each ${\mathrm{\ensuremath{\Gamma}}}_{5}$ state, a small splitting in the first-excited doublet was clearly observed at low temperatures.