Interaction of spin waves and spin-polarized current with magnetic inhomogeneities in nanostructured ferromagnetic materials
A theory is developed for the propagation of spin waves in heterogeneous ferromagnetic systems. The theory provides for the generation of spin waves using a spin-polarized current and control of the process of propagation of spin waves in such media. In particular, the mechanism of excitation of dipole-exchange spin waves in a multilayer ferromagnetic nanosystem is presented. The dispersion laws of dipole-exchange spin waves in a multilayer ferromagnetic nanosystem in the presence of a spin-polarized current are obtained, as well as the parameters of effective dissipation and the conditions for generation of a spin wave. The spectral characteristics of spin waves are found for two configurations of a one-dimensional and one configuration of a two-dimensional magnonic crystal. The presence of a band structure in the spectra of the studied magnonic crystals is shown. The characteristics of the process of refraction of exchanged spin waves in inhomogeneous ferromagnetic structures such as spin lenses based on ferromagnetic heterogeneous structures for bulk spin waves in the exchange approximation with taking into account the exchange inhomogeneity of interfaces, which are means of controlling the processes of propagation of spin waves in ferromagnetic media, are found. For a number of configurations of spin lenses, it has been shown that it is possible to effectively control the intensity of the spin wave, as well as to control the transparency of such inhomogeneities, which makes it possible to use them both as lenses and as mirrors, depending on the magnitude of the external field and the wave frequency. The characteristics of the field and frequency dependences of the refractive indices of spin waves and the focal lengths of spin lenses based on uniaxial ferromagnets in an external constant magnetic field are obtained. The existence of a narrow transition zone in the field and spectral dependences of refractive indices and reflection coefficients was also discovered, in which a sharp jump in the amplitude of the wave reflected from the boundary of two homogeneous media occurs.