Tunneling of magnetization versus spin–phonon and spin–spin transitions in LiY0.998Ho0.002F4

Abstract Strong hyperfine coupling in a 0.2% holmium-doped LiYF 4 single crystal induces staircase-like hysteresis loops of the magnetization at very low temperatures. The field sweep rate dependence of hysteresis loops allows the study of two different regimes in the magnetic relaxation of these weakly coupled magnetic moments. At slow field sweep rates, quantum tunneling of the magnetization occurs at avoided level crossings in the low-energy scheme of a single ion Ho 3+ . At faster sweep rates, nonequilibrated spin–phonon and spin–spin transitions, mediated by weak dipolar interactions, lead to magnetization oscillations and additional steps.