Resonant tunneling of magnetization in Mn¹² acetate complex

Based on low-temperature measurements on oriented crystallites of Mn¹² acetate complex, we report strong evidence for resonant tumleling of magnetization for these high spin molecules: we observed periodic steps in the hysteresis loops, periodic marked peaks in the magnetic relaxation rate at the fields corresponding to these steps, and a concomitant periodic decrease of the blocking temperature with magnetic field. We attribute these observations to thermally assisted resonant tunneling of the magnetization in a double well potential and propose a detailed model to account for our results.