Theory of nonequilibrium intrinsic spin torque in a single nanomagnet

In a single nanomagnet with spin-orbit interactions, the electrical current can generate a nonequilibrium spin density that gives rise to a spin torque on the magnetization. This spin torque does not involve spin transfer mechanism and originates from the band structure itself. We show that this spin torque can be effectively used to switch the direction of the magnetization and the critical switching current density could be as low as 10^4--10^6 A/cm^2 for a number of magnetic systems. Several magnetic systems for possible experimental realization are discussed.