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

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 (Formula presented) and (Formula presented) 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.