  The switching probability of a single-domain ferromagnet under spin-current
excitation is evaluated using the Fokker-Planck equation(FPE). In the case of
uniaxial anisotropy, the FPE reduces to an ordinary differential equation in
which the lowest eigenvalue $\lambda_1$ determines the slowest switching
events. We have calculated $\lambda_1$ by using both analytical and numerical
methods. It is found that the previous model based on thermally distributed
initial magnetization states \cite{Sun1} can be accurately justified in some
useful limiting conditions.
