THE HYPERFINE SPLITTING OF THE GROUND-STATE AND FIRST EXCITED-STATE OF HOLMIUM IN YTTRIUM HYDROXIDE

We have studied the field dependence of the hyperfine splitting of Ho- 165 in yttrium hydroxide by spin echo NMR at liquid helium temperature s and in fields up to 8 T. Hyperfine spectra have been obtained from t he electronic ground state and from the first excited state. The measu red hyperfine splittings are compared with theoretical results obtaine d by diagonalizing the complete electronic-nuclear Hamiltonian for the nominally I-5(8) ground multiplet of Ho3+ using crystal field paramet ers derived from optical spectroscopy. There is close agreement betwee n the measured and calculated quadrupolar and octupolar splittings, bu t we find a significant difference between the measured and calculated dipolar splittings, especially when allowance is made for J mixing. A greement is restored, to within the uncertainties, if the currently ac cepted value of the dipolar hyperfine coupling coefficient for the fre e Ho3+ ion is reduced by 1.3%. Independent evidence for a reduction of that order will be presented in a later publication. The ratio of nuc lear to electronic antishielding factors for Ho3+ in found to be gamma (N)/gamma(E) = 148 +/- 10, in close agreement with the value obtained in pure holmium hydroxide.