On the ground state of Ho3+ in ferromagnetic HoAl2

Abstract

The ground state of the holmium ion in ferromagnetic HoAl2 is discussed in the light of available experimental evidence, including hitherto unpublished NMR measurements on165Ho. The measured quadrupole splitting is not consistent with the ground state derived from neutron form factor experiments, but is compatible with exchange and crystal field parameters derived from magnetization measurements and neutron spectroscopy in the context of the conventional three-parameter mean-field model. A more detailed analysis of the NMR data indicates that the exchange interaction in HoAl2 is over 20% stronger than that derived, using mean-field theory, from the Curie temperature. Using the revised exchange constant and a weighted average of published crystal field parameters, we obtainμ = (9.39 ± 0.05)μ B for the moment on the Ho3+ ion atT =0. The contribution of orbitally polarized conduction electrons to the hyperfine field at the holmium nucleus is estimated to be (−1.4±2.0) T.