Field dependence of the hyperfine splitting of holmium in holmium hydroxide

The hyperfine splitting of ¹⁶⁵Ho in holmium hydroxide has been studied by spin-echo NMR at liquid-helium temperatures in fields up to 8 T. The behaviour of the dipolar splitting in fields below 0.5 T confirms that the hyperfine parameters are not thermally averaged and that the NMR signals arise solely from ions in the electronic ground state. The field dependence of the hyperfine splitting is not accurately described by crystal-field parameters derived from magnetic susceptibility measurements on Ho(OH)₃, but is in close agreement with calculations based on parameters derived from optical spectroscopy of Ho³⁺ in Y(OH)₃. The following quantities are derived from the measurements: spontaneous magnetisation and longitudinal susceptibility of Ho(OH)₃ at T=0:M₀=(1.181+or-0.001) MA m^-1 and chi /sub ///=0.0146+or-0.0005; ratio of nuclear to electronic anti-shielding factors for Ho³⁺ in the hydroxide: gamma _N/ gamma _E=149+or-15.