  We study the influence of the spin torque, which depends on the space and
time derivative of magnetization, on magnetization reversal time in a
ferromagnetic fine particle. The spin torque operates to dissipate the angular
momentum of the magnetization precession, and the torque increases in a spin
vortex structure. We calculate the magnetization reversal time under a DC
magnetic field using the Landau-Lifshitz-Gilbert equation containing a spin
torque term. We found that the spin torque changes the magnetization switching
speed significantly during the reversal process by maintaining a spin vortex in
an intermediate state.
