Ferromagnetic nanojunctions at a high current-induced spin injection

A perpendicular current that flows through a ferromagnetic nanojunction (a layered nanosized spinvalve structure containing two ferromagnetic metal layers separated by a spacer) is studied. The spacer is thick enough to prevent the exchange coupling of the layers in the absence of the current. On the other hand, the spacer is sufficiently thin and does not affect the spin polarization in the presence of the current. Conditions for a relatively high current-induced spin injection are found. Under such conditions, the concentration of the injected nonequilibrium spins can be equal to or even greater than the equilibrium concentration and several new effects are observed: The threshold of the exchange switching by the current decreases by several orders of magnitude owing to the matching of the spin resistances of the layers, the threshold additionally decreases in the presence of an external magnetic field in the vicinity of the orientational phase transition, and multistability emerges (several stable noncollinear orientations of magnetization correspond to a single value of the current). Switching appears to be irreversible.