Nuclear magnetic resonance in holmium vanadate, HoVO 4

Abstract

In HoVO 4 the Ho 3+ ion, 4f 105 I 8 , 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 H N = − γ 1 h B 2 I 2 − γ ⊥ h ( B x I x + B y I y ) + P [ I z 2 − 1 3 I ( I + 1 ) ] . The parameters have been determined by nuclear magnetic resonance measurements on 165 Ho and 51 V at frequencies of 500 and 11 MHz respec­tively. The dependence of ( γ ┴ /2π) in HoVO 4 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 HoVO 4 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 .