  Magnetic junction is considered which consists of two ferromagnetic metal
layers, a thin nonmagnetic spacer in between, and nonmagnetic lead. Theory is
developed of a magnetization reversal due to spin injection in the junction.
Spin-polarized current is perpendicular to the interfaces. One of the
ferromagnetic layers has pinned spins and the other has free spins. The current
breaks spin equilibrium in the free spin layer due to spin injection or
extraction. The nonequilibrium spins interact with the lattice magnetic moment
via the effective s-d exchange field, which is current dependent. Above a
certain current density threshold, the interaction leads to a magnetization
reversal. Two threshold currents are found, which are reached as the current
increases or decreases, respectively, so that a current hysteresis takes place.
The theoretical results are in accordance with the experiments on magnetization
reversal by current in three-layer junctions Co/Cu/Co prepared in a pillar
form.
