  The current dependence of the switching barrier for spin torque switching of
an in-plane magnetized ferromagnet was studied. Two scaling currents, I_{c}$
and I_{c}^{*}(>I_{c}), were introduced to distinguish the magnetization
stability. In the low-current region I<I_{c}, the switching barrier is linear
to the current with another scaling current \tilde{I}_{c}, while such linear
scaling does not hold in the high-current region I_{c} < I < I_{c}^{*}. The
linear scaling is valid for the high temperature and the long current pulse
duration time.
