HEAT-CAPACITY ANOMALIES INDUCED BY MAGNETIZATION QUANTUM TUNNELING INA MN12O12-ACETATE SINGLE-CRYSTAL

A particularly sensitive heat capacity measuring device has allowed us to measure the tunneling process of Mn12O12-acetate single crystals ( mass: 1 and 20 mu g) from the irreversible tunneling process below the blocking temperature T-B to the reversible resonant tunneling process above T-B. Above the T-B (typically 3.5 K) we find specific heat anom alies at the magnetic field values that correspond to the crossing of spin up and spin down levels of different magnetic quantum numbers. Be low T-B, heat relaxation pulses at the crossing of crystal field level s are observed for fields applied antiparallel to the initial magnetiz ation. These measurements give a new scope to Mn12O12-acetate investig ations and show the great interest of nanocalorimetry for studies of b ig magnetic molecules.