The dissertation is devoted to the research of features and character of spin wave (SW) propagation in ordered nanoscale elements with structured interfaces in both ferromagnets (FM) and antiferromagnets (AFM) and is aimed at gaining new knowledge in the prospective direction of modern research. FM and AFM thin films with ordered nanoscale elements (antidots), in particular their multilayer compositions, with appropriately structured interfaces, which are considered as composite materials of both infinitely thin and finite thickness, were selected for the study. SWs open the prospect of non-volatile devices that can be competitive with modern devices. The main advantages of using magnetic materials in electronic and telecommunication devices are their controllability by an external magnetic field, energy independence, and programmability. Artificial structuring of nanoscale patterns provides an excellent opportunity to modify their excitation spectra, and therefore to design materials with unpredictable properties that can potentially meet the constant need for faster manipulation of larger amounts of information, larger storage capacities with reduced write and read time, and the constant demand for miniaturization and energy efficiency, since the transmission, storage and manipulation of information is an important part of high technology.
The main part of the dissertation consists of five sections.
The first section is devoted to a detailed analysis of the propagation of SWs in FM and AFM and the study of boundary conditions at various structured interfaces.
In the second section of the dissertation, the method is developed for an effective guiding of SWs, which coherently propagate, within magnetic nanostructures (waveguides). The method is based on anomalous refraction in a thin FM layer in the form of a slab with a graded index (GRIN), along which a gradual change in the magnetic parameters of the material allows to tilt the front of transmitted SWs and control the bending. Based on analytical calculations of the phase shift acquired by the SW due to changes in the magnetic parameters of the material in a limited region, it is shown that the refraction of the SW can be changed for desired angle. This phenomenon requires a linear change in the phase of the transmitted waves near the interface where the refraction occurs. Its description requires a generalization of Snell's law, which is used to guide SWs in waveguides for the first time. For this purpose, an analytical model was developed for the exchange SW scattering on a homogeneous FM slab of finite width – GRIN slab embedded in FM layer – waveguide. Minimizing the total energy, the boundary conditions at the interfaces between the GRIN slab and its surrounding on both sides are derived, and the complete dependence between the phase shifts and the amplitudes of the incident and transmitted SWs is investigated.
In the third section, the boundary conditions between FM and two-sublattice AFM for the magnetization dynamics problems in the continuous medium approximation for both the finite thickness interface and the infinitely thin interface are derived. Taking into account the homogeneous and inhomogeneous exchange, the propagation of a surface evanescent SW into the AFM is investigated in a case when this SW falls onto the interface from the FM.
The fourth section presents a new concept that makes an essential step towards solving a critical problem of controlling SWs propagation through interfaces of AFM thin film with other magnetic media by introducing a new physical characteristic of the interfaces of finite thickness – a degree of sublattice noncompensation of AFM (DSNA). The DSNA value can be changed by designing interfaces with diagonal-like and curvilinear geometry. A theory that describes SWs propagation through any designed AFM/FM interface considering a variable DSNA is presented and the generalized boundary conditions are proposed. It is demonstrated that SWs transmission from AFM to FM is made possible with a specific design of the interface.
In the fifth section, an analytical model of FM resonance in a Py FM thin film with a circular antidot is constructed. The linearized Landau-Lifshitz equation was solved as an eigenproblem in the direct space to create an analytical model of small deviations from the equilibrium values of magnetic moment and magnetic field. It was found that the main cause of inhomogeneous oscillations is the magnetostatic field caused by the presence of the antidot. The model showed that there is a maximum of the amplitude of the demagnetization field localized near the edge of the antidot, and the amplitude decreases with increasing distance from the edge. The conditions of local FM resonances, which vary at different distances from the edge of the antidot due to the heterogeneity of the magnetostatic field, were also determined.
