The hyperfine interaction of holmium in ferromagnetic rare earth alloys

Abstract

Spin echo measurements have been made, at liquid helium temperatures, on ¹⁶⁵Ho in ferromagnetic alloys of holmium with gadolinium, terbium and dysprosium. Intra and extraionic contributions to the hyperfine interaction are discussed, with particular emphasis on conduction electron effects. The hyperfine field B_p due to conduction electrons polarized by the parent holmium ion is found to be +12 T, and the field B_n due to conduction electrons polarized by neighbouring ions is -8.3 S T, where S is the mean ionic spin of the alloy. The contributions from individual neighbour ions to B_n are found to be additive and of moderately long range, and to depend only on the spin of the polarizing ion. Electric quadrupole splittings in the Ho-Tb and Ho-Dy alloys indicate that the electric field gradient due to conduction electrons exceeds that due to the ionic lattice by a factor of about seven.