arXiv2010
Two channels of the sd exchange interaction are considered in magnetic junctions. The first channel describes the interaction of transversal spins with the lattice magnetization. The second one describes the interaction of longitudinal spins with magnetization. We show the longitudinal channel leads to a number of significant effects: 1) drastic lowering of the current instability threshold down to three (or even more) orders of magnitude; 2) creation of large enough distortion of equilibrium due to current driven spin injection leading to inversion of energy spin subband populations and laser-like instability in THz frequency range at room temperature. External magnetic field may tend to lower additionally the instability threshold due to the proximity effect of purely magnetic reorientation phase transition. This effect demonstrates the new properties: the giant magnetoresistance (GMR) becomes strongly current dependent and the exchange switching becomes of very low threshold. We derived some matching condition that should be satisfied to achieve high spin injection level. Some characteristic quantities were appeared in the condition. We investigated also the junctions having variable lateral dimensions of the layers, for example, a ferromagnetic rod contacting with a very thin ferromagnetic film. Large enhancement of the current density may appear near the contact region leading to the spin injection luminescence.