Multilayers as spin-wave emitting diodes

Magnon-electron interaction is enhanced in the vicinity of an interface between ferromagnetic and normal layers, in metallic thin films. When a de current crosses this interface, stimulated emission of spin-waves is predicted to take place. Beyond a certain critical current density similar or equal to 10(7) A/cm(2), a spontaneous precession of the magnetization is predicted to arise. This SWASER (Spin Wave Amplification by Stimulated Emission of Radiation) is the magnetic equivalent of the injection laser. In the earlier theories, the thickness of the precessing magnetic layer was assumed to be larger than the electron mean free path. We now treat the case of general value of that thickness L-2(x). The current-induced amplification rate of spin-waves is proportional to L-2(x) in the limit L-2(x) similar or equal to 0, and goes through a maximum for L-2(x) similar or equal to pi/\k(up arrow) - k(down arrow)\. Here, k(up arrow) and k(down arrow) are the spin-up and spin-down Fermi wave numbers. At larger L-2(x), the amplification rate of spin-waves decreases towards zero. On that general decrease are superposed damped periodic variations of wavelength similar or equal to 2 pi/\k(up arrow) - k(down arrow)\. (C) 1997 American Institute of Physics.