Effects of the environment on nonadiabatic magnetization process in uniaxial molecular magnets at very low temperatures

Abstract

We discuss the effect of the thermal environment on the low-temperature response of the magnetization of uniaxial magnets to a time-dependent applied magnetic field. At very low temperatures the stepwise magnetization curves observed in molecular magnets such as ${\mathrm{Mn}}_{12}$ and ${\mathrm{Fe}}_{8}$ display little temperature dependence where the apparent thermal assisted process are suppressed. We show that the changes of the magnetization at each step cannot be analyzed directly in terms of a quantum-mechanical nonadiabatic transition. In order to explain this nonadiabatic behavior, we study the quantum dynamics of the system weakly coupled to a thermal environment and propose a relation between the observed magnetization steps and the quantum-mechanical transition probability due to the nonadiabatic transition.