Nuclear spin driven quantum relaxation in LiY0.998Ho0.002F4 - art. no. 057203

Staircaselike hysteresis loops of the magnetization of a LiY0.998Ho0.002F4 single crystal are observed at subkelvin temperatures and low field sweep r ates. This behavior results from quantum dynamics at avoided level crossing s of the energy spectrum of single Ho3+ ions in the presence of hyperfine i nteractions. Enhanced quantum relaxation in constant transverse fields allo ws the study of the relative magnitude of tunnel splittings. At faster swee p rates, nonequilibrated spin-phonon and spin-spin transitions, mediated by weak dipolar interactions, lead to magnetization oscillations and addition al steps.