High field magnetization process in a dodecanuclear Fe(III) ring cluster

A high field magnetization technique is applied to study the field-dependent behaviors of the molecular magnet, dodecanuclear Iron(III) ring cluster [Fe(OCH₃)₂(dbm)]₁₂, in which twelve numbers of Fe³⁺ (S = 5/2) ions form a finite chain ring, where dbm = dibenzoylmethane. The low-lying states of the spin manifold are dramatically revealed by the observation of magnetization process using pulsed high magnetic field up to 55 T at temperature down to 0.1 K. We observed four distinct magnetization steps with nearly equal field separation of 10T, arising from energy-level crossings for the discrete quantum states in the finite spin system. We discuss the structure of energy levels and the relaxation phenomena in the magnetization process around the level-crossing fields. It is found that the anomalous magnetization curve observed at 1.3 K, showing an unusual shape with characteristic hysteresis for increasing and decreasing field, is well reproduced by Phonon Bottleneck effect caused by the week heat exchange between sample and liquid-He bath during the fast field passage. Our results are compared and discussed with those obtained in the other iron magnets showing the step-like magnetization process due to quantum discrete energy levels.