Deceptive Apparent Nonadiabatic Magnetization Process

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 sufficiently low temperatures the staircase magnetization curves observed in molecular magnets such as Mn_{12} and Fe_8 display little temperature dependence. However the changes of the magnetization at each step do not seem to be directly related to the probability for a quantum mechanical nonadiabatic transition. In order to explain this deceptive apparent nonadiabatic behavior, we study the quantum dynamics of the system in a thermal environment and propose a relation between the observed magnetization steps and the quantum mechanical transition probability due to the nonadiabatic transition.