Nuclear magnetic resonance in holmium vanadate, HoVO 4

In HoVO₄ the Ho³⁺ ion, 4f¹⁰⁵I₈, experiences a crystal field of tetragonal symmetry which produces a ground state singlet and a nearby excited doublet at 21 cm^-1 and at low temperatures the material behaves as a Van Vleck paramagnet with high anisotropy. The nuclear Zeeman interaction is greatly enhanced through the hyperfine interaction and the nuclear Hamiltonian may be written HN=−γ1hB2I2−γ⊥h(BxIx+ByIy)+P[Iz2−13I(I+1)]. The parameters have been determined by nuclear magnetic resonance measurements on ¹⁶⁵Ho and ⁵¹V at frequencies of 500 and 11 MHz respec­tively. The dependence of (γ_┴/2π) in HoVO₄ on sample shape is analysed, and shown to be consistent with the value 1526(3) MHz T^-1 for 165Ho in YV0_4, while │P/h│= 25.9(3) MHz in HoVO₄ and 25.3(2) MHz in YVO4 (T ≤ 2K). The origins of the line width and quadrupole interaction are discussed. The high degree of anisotropy prohibits a direct measurement of γ_║ but it is extimated that (γ_//γ_┴) ˜ 10^-2.