  We have investigated the current-induced spin transfer torque of a
ferromagnet-insulator-ferromagnet tunnel junction by taking the spin-flip
scatterings into account. It is found that the spin-flip scattering can induce
an additional spin torque, enhancing the maximum of the spin torque and giving
rise to an angular shift compared to the case when the spin-flip scatterings
are neglected. The effects of the molecular fields of the left and right
ferromagnets on the spin torque are also studied. It is found that $\tau
^{Rx}/I_{e}$ ($\tau ^{Rx}$ is the spin-transfer torque acting on the right
ferromagnet and $I_{e}$ is the tunneling elcetrical current) does vary with the
molecular fields. At two certain angles, $\tau ^{Rx}/I_{e}$ is independent of
the molecular field of the right ferromagnet, resulting in two crossing points
in the curve of $\tau ^{Rx}/I_{e}$ versus the relevant orientation for
different molecular fields.
