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Magnon-magnon and magnon-phonon processes in magnetoelectronic and magnetocaloric element

Work number - M 10 AWARDED

Presented Institute of Magnetism of National Academy of Sciences of Ukraine and Ministry of Education and Science of Ukraine

A. O. Kosogor, D. Sci., R. V. Verba, D. Sci., D. V. Slobodianiuk, Ph. D

The aim of the work is the investigation of magnon-magnon and magnon-phonon processes in magnetic nanostructures and functional magnetic.

The authors studied the features of multimagnon processes in magnetic micro- and nanostructures, such as nonresonant character and the appearance of specific selection rules, as well as the effects of such processes on nonlinear ferromagnetic resonance. The influence of three-magnon confluence on spin pumping in ferromagnetic - heavy metal bilayers and the possibility of spin pumping enhancement due to multimagnon processes are shown.

The existence of processes in magnetic nanosystems similar to the kinetic instability in magnetic films, in particular, the excitation of the lowest mode of the system at a high pumping level, has been demonstrated. Such processes is shown to be an effective mediator of the magnon condensation, in particular, they may lead to the reduction of the condensation threshold.

Methods for increasing of generation power and coherence of spin-Hall oscillators by reduction of the dimensionality of the oscillator active zone to quasi-onedimensional and application of a nonuniform driving current have been proposed and investigated. The possibility of transition from single-mode to dual-mode generation in spin-torque nanooscillators under the influence of strong thermal noise is shown.

A method for the creation of high-speed reconfigurable magnonic crystals based on magnetic nanodots arrays is developed. The crystal state is reconfigured under short magnetic field pulses having duration of 50-100 ns, which is three orders of magnitude faster than previously developed analogues. It is shown that the properties of the final state of the array after the application of the pulse are determined by the growth rate of the collective modes instability near the point of spin-wave spectrum softening.

A theory of the direct and inverse magnetocaloric effects in metamagnetic alloys, based based on the fundamental thermodynamic relationship between the free energy of magnetic exchange of the material and the entropy function, is developed.

A special version of the Landau phenomenological theory of phase transitions has been developed for the description of the nanoparticle influence on the properties of martensitic alloys. Martensitic alloys having a marked change in volume during martensitic transformation are shown to be promising materials for the optimization of performance characteristics by addition of nanoparticles.

The obtained fundamental results open the way for the improvement of existing and creation of novel devices of spintronics, functional materials of magnetocalorics and microwave electronics.

Number of publications: 23 scientific papers (all are published in journals with assigned impact-factor in English). Total number of citations / h-index of the work, according to the databases, are: Web of Science – 205/ 7, Scopus– 233/ 9, Google Scholar – 293/ 10.