The hyperfine interaction of Ho3+ in gold

Summary Ho in Au exhibits interesting paramagnetism. The full J=8 angular momentum is partially quenched by the crystal field. At sufficiently low temperatures, however, the ion acts like a Van Vleck paramagnet although it has a non-magnetic doublet at ground state instead of a singlet ground state. An applied magnetic field definitely is enhanced by the large hyperfine interaction and excited ground state mixing. This results in anisotropy all the way up to 1 K which makes^166m HoAu an excellent candidate for a secondary thermometer in the 10mK-1 K region. The complete interpretation of the^166m Ho³⁺Au experiments will require sizeable computing times.