  Microwave radiation applied to single-molecule magnets can induce large
magnetization changes when the radiation is resonant with transitions between
spin levels. These changes are interpreted as due to resonant heating of the
sample by the microwaves. Pulsed-radiation studies show that the magnetization
continues to decrease after the radiation has been turned off with a rate that
is consistent with the spin's characteristic relaxation rate. The measured rate
increases with pulse duration and microwave power, indicating that greater
absorbed radiation energy results in a higher sample temperature. We also
performed numerical simulations that qualitatively reproduce many of the
experimental results. Our results indicate that experiments aimed at measuring
the magnetization dynamics between two levels resonant with the radiation must
be done much faster than the >20-microsecond time scales probed in these
experiments.
