Further studies of the enhanced nuclear magnet HoVO4 I. The crystal field and the Zeeman spectrum

A novel approach is adopted to fit the experimental results for the Van Vleck paramagnet HoVO4. Within the ground manifold 5I8, J = 8, the five parameters for a crystal field of tetragonal symmetry are adjusted to give values in agreement with the optical spectrum for the lowest energy levels: the ground singlet, the first excited doublet at 21 cm-1, and the (accidental) triplet at 47 cm-1. Within experimental error (of order 1 cm-1), this agreement is not impaired by a small modification in which all the crystal field parameters are multiplied by a factor 1.0225. This factor is introduced to give the correct value of the enhanced nuclear magnetic resonance frequency for the stable isotope 165Ho (I = 7/2), known to 0.3% (Bleaney et al. Proc. R. Soc. Lond. A 362, 179 (1978)). The optical Zeeman effect, calculated therefrom, is in good agreement with that observed experimentally for the lowest levels in magnetic fields up to 15 T, directed along the [100], [110] and [001] axes (Battison et al. Phys. Lett. A 55, 173 (1975); J. Phys. C 10, 323 (1977)).