Heat Capacity Anomalies Induced by Magnetization Quantum Tunneling in a Mn12O12-Acetate Single Crystal

A particularly sensitive heat capacity measuring device has allowed us to measure the tunneling process of ${\mathrm{Mn}}_{12}{\mathrm{O}}_{12}$-acetate single crystals (mass: $1$ and $20\mu \mathrm{g}$) 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 $3.5\mathrm{K}$) we find specific heat anomalies at the magnetic field values that correspond to the crossing of spin up and spin down levels of different magnetic quantum numbers. Below $T_B$, heat relaxation pulses at the crossing of crystal field levels are observed for fields applied antiparallel to the initial magnetization. These measurements give a new scope to ${\mathrm{Mn}}_{12}{\mathrm{O}}_{12}$-acetate investigations and show the great interest of nanocalorimetry for studies of big magnetic molecules.