Gusieva Y. Spin and acoustic waves in the system with flat inhomogeneous defects

The dissertation is devoted to the research of the behavior of spin and acoustic waves in systems with inhomogeneities in which the broken inversion spatial axis symmetry and with magnetoelastic defects. In particular, the influence of the broken inversion spatial axis symmetry at the boundary of two ferromagnets on the propagation of spin waves, the model of excitation of bulk spin waves by Kosevich's acoustic wave and the influence of magnetic inclusions in the elastic system on the propagation of acoustic waves are considered. The current state of the problems that currently exist regarding the influence of inhomogeneous defects on the magnetic properties of materials is reflected in the first part of this paper. A large number of works are devoted to the description of effects in magnetic materials without an inversion center, but for all massive materials the effects are weak. Therefore, attention was drawn to the broken inversion symmetry in inhomogeneous interfaces and in defect layers on the surface. In a given topic, many important problems have not yet been solved, one of which is to take into account the influence of the boundary interface in which the symmetry of inversion is broken. In addition, the analysis of the perspects of combining the advantages of magnonics with phononics in nanoelectronics gives a request to study methods for excitation of spin waves in thin films by surface acoustic waves and to solve the problem of rapid damping of spin waves due to magnetoacoustic devices. Part two is devoted to the study of the behavior of spin waves in a system of two ferromagnets on the boundary of which the symmetry of the inversion of the spatial axis is broken. Based on the theoretical model, which takes into account the effect of broken inversion spatial axis symmetry at the boundary between two ferromagnets of finite thickness on the excitation of spin waves, an additional condition to the dispersion law is obtained, which modifies a discrete spectrum of allowed frequencies. It is established that the value of the symmetry breaking parameter is proportional to the value of the exchange constant in the boundary layer between materials and inversely proportional to the thickness of the boundary between ferromagnets. It is found conditions for increasing the influence of the inversion symmetry breaking parameter at the boundary of two ferromagnets on a change in the value of the coefficient of transmission or reflection of the spin wave from the boundary and on the value and sign of the phase shift between the phases of the transmitted and the incident spin wave. Thus, the symmetry breaking parameter is an additional factor of phase shift control. It is established that the nonreciprocity effect occurs when the spin wave propagates in a system of two identical ferromagnets as a result of breaking the symmetry of the inversion of the spatial axis at the boundary between them. It is determined that the value of the inversion symmetry breaking parameter at the boundary between two ferromagnetic materials can be a method of controlling the angle of the nonlinear spin wave in the second material when the linear spin wave is excited in the first. In the third part, the theoretical modeling of the excitation of bulk spin waves in a ferromagnetic system by a surface acoustic Kosevich wave in a planar defective layer was carried out. On the basis of the theoretical model the conditions for excitation of the maximum amplitude of magnetic excitations were determined. The fourth section theoretically investigated the class of energy-efficient magneto-elastic devices in which signals are carried by transverse acoustic waves while the bias magnetic field controls their scattering from a magneto-elastic slab. It is determined that by tuning the bias field, one can alter the resonant frequency at which the propagating acoustic waves hybridize with the magnetic modes. It is shown that the frequency dependence of the the waves’ reflection coefficient from the inclusions has a Fano-like lineshape, which is particularly sensitive to magnetic damping. It is shown that the metamaterial approach is to consider an acoustic wave in a periodic array of thin magnetic layers embeded in a nonmagnetic matrix is really useful for magnetoacoustics. Hybrid metamaterials, formed by 1D arrays of resonators, magnify the effect of magnetoelastic coupling upon the acoustic scattering, thereby mitigating the Gilbert damping to tolerable levels. The considered structures are regulated by the applied displacement field and demonstrate rich and complex behavior, such as induced transmission and Bormann asymmetry. It is assumed that the characteristics shown here will be useful in the creation of sensors, starters, radio frequency modulators and tunable magnetic devices.