  The macroscopic magnetic moment of a superparamagnetic system has to overcome
an energy barrier in order to switch its direction. This barrier is formed by
magnetic anisotropies in the material and may be surmounted typically after
10^9 to 10^12 attempts per second by thermal fluctuations. In a first step, the
associated switching rate may be described by a Neel-Brown-Arrhenius law, in
which the energy barrier is assumed as constant or a given temperature. Yet,
magnetic anisotropies in general depend on temperature themselves which is
known to modify the Neel-Brown-Arrhenius law. We illustrate quantitatively the
implications of a temperature-dependent anisotropy on the switching rate and in
particular for the interpretation of the prefactor as an attempt frequency. In
particular, we show that realistic numbers for the attempt frequency are
obtained when the temperature dependence of the anisotropy is taken into
account.
