Magnetic-field-dependent thermodynamics of Mn12-acetate single crystals at low temperatures

Thermal measurements of single microcrystals of Mn-12 acetate have been performed with a particularly sensitive nanocalorimeter. Heat-capacity measurements as a function of applied magnetic field demonstrate magnetization quantum tunneling at the crossing of crystal-field levels. We present a theoretical model of the magnetic heat capacity of Mn-12 acetate that approximately agrees with experimental results. Temperature measurements as a function of a slowly scanned magnetic field confirm earlier magnetization measurements and suggest that the thermal coupling between bath and sample, as well as the thermal conductivity of the crystals, play a major role in the magnetization reversal. [S0163-1829(98)06041-X].