Аннотация
The time evolution of the magnetization of a magnetic molecular crystal
is obtained in an external time-dependent magnetic field, with sweep
rates in the kT/s range. We present the ``exact numerical'' solution
of the time-dependent Schrodinger equation, and show that the steps in
the hysteresis curve can be described as a sequence of two-level
transitions between adiabatic states. The multilevel nature of the
problem causes the transition probabilities to deviate significantly
from the predictions of the Landau-Zener-Stuckelberg model. These
calculations allow the introduction of an efficient approximation method
that accurately reproduces the exact results. When including phase
relaxation by means of an appropriate master equation, we observe an
interplay between coherent dynamics and decoherence. This decreases the
size of the magnetization steps at the transitions, but does not modify
qualitatively the physical picture obtained without relaxation.
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