Institute of Magnetism of NAS of Ukraine

Kiev, Ukraine

Institute of Magnetism of NAS of Ukraine

Kiev, Ukraine
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Kruglyak V.V.,University of Exeter | Davies C.S.,University of Exeter | Tkachenko V.S.,Donetsk National University | Gorobets O.Yu.,National Technical University of Ukraine | And 4 more authors.
Journal of Physics D: Applied Physics | Year: 2017

We report a theoretical study of the spin-wave band spectrum of magnonic crystals formed by stacking thin-film magnetic layers, with general assumptions about the properties of the interfaces between the layers. The use of the Barnaś-Mills magnetization boundary conditions has enabled us to systematically trace the origin of the magnonic band gaps in the spin-wave spectrum of such systems. We find that the band gaps are a ubiquitous attribute of a weakened interlayer coupling and a finite interface anisotropy (pinning). The band gaps in such systems represent a legacy of the discrete spin-wave spectrum of the individual magnetic layers periodically stacked to form the magnonic crystal rather than resulting from Bragg scattering. At the same time, magnonic crystals with band gaps due to the Bragg scattering can be described by natural boundary conditions (i.e. those maintaining continuity of the magnetization direction across the whole sample). We generalize our conclusions to systems beyond thin-film magnonic crystals and propose magnonic crystals based on the ideas of graded-index magnonics and those formed by Fano resonances as a possible way to circumvent the discovered issues. © 2017 IOP Publishing Ltd.

Kruglyak V.V.,University of Exeter | Gorobets O.Yu.,National Technical University of Ukraine | Gorobets O.Yu.,Institute of Magnetism of NAS of Ukraine | Gorobets Y.I.,Institute of Magnetism of NAS of Ukraine | Kuchko A.N.,Donetsk National University
Journal of Physics Condensed Matter | Year: 2014

We develop a systematic approach to derive boundary conditions at an interface between two ferromagnetic materials in the continuous medium approximation. The approach treats the interface as a two-sublattice material, although the final equationsconnect magnetizations outside of the interface and therefore do not explicitly depend on its structure. Instead, the boundary conditions are defined in terms of some average properties of the interface, which may also have a finite thickness. In addition to the interface anisotropy and symmetric exchange coupling, this approach allows us to take into account coupling resulting from inversion symmetry breaking in the vicinity of the interface, such as the Dzyaloshinskii-Moriya antisymmetric exchange interaction. In the case of negligible interface anisotropy and Dzyaloshinskii-Moriya exchange parameters, the derived boundary conditions represent a generalization of those proposed earlier by Barnas̈ and Mills and are therefore named 'generalized Barnas̈-Mills boundary conditions'. We demonstrate how one could use the boundary conditions to extract parameters of the interface via fitting of appropriate experimental data. The developed theory could be applied to modeling of both linear and non-linear spin waves, including exchange, dipole-exchange, magnetostatic, and retarded modes, as well as to calculations of non-uniform equilibrium micromagnetic configurations near the interface, with a direct impact on the research in magnonics and micromagnetism. © 2014 IOP Publishing Ltd.

Titenko A.N.,Institute of Magnetism of NAS of Ukraine | Demchenko L.D.,National Technical University of Ukraine
Journal of Materials Engineering and Performance | Year: 2012

This article presents the deformation behavior of aged ferromagnetic alloys of Fe-Ni-Co-Ti-Cu system caused by phase transitions. The basic characteristic temperatures of martensitic transformation (MT) of the alloys were determined from temperature dependences of low-field magnetic susceptibility. The coefficients of thermal expansion of high- and low-temperature phases, as well as values of volume effect were obtained from dilatometric data. Peculiarities of deformation behavior were studied from the analysis of stress-strain curves, registered at uniaxial tension. It was found that investigated alloys have a substantial superelastic deformation and a low value of the temperature hysteresis of MTwith the volume effect of 2%, which is typical for thermoelastic alloys of Fe-Ni-Co-Ti-Cu system. © ASM International.

Gorobets Y.I.,Institute of Magnetism of NAS of Ukraine | Reshetnyak S.O.,Kharkiv Polytechnic Institute
Journal of Nano- and Electronic Physics | Year: 2012

In this paper the dependencies are obtained of spin wave reflection coefficients on frequency and external magnetic field for ferromagnetic structure in the exchange mode, when the influence of magnetostatic part of energy is neglected as compared with exchange one. It is shown that ferrogarnet structure, having very small damping parameter, is good for high-quality filtration of spin waves because it gives large change of reflection coefficient in small intervals of frequencies and external magnetic fields. © 2012 Sumy State University.

Ivanov B.A.,Institute of Magnetism of NAS of Ukraine
Low Temperature Physics | Year: 2014

Investigations of excitation of spin dynamics in transparent antiferromagnets (AFM) under the action of femtosecond laser pulses are reviewed. A variety of observed effects is considered in the context of a unified approach. The analysis is based on the nonlinear sigma model for the antiferromagnetism vector L with taking into account effective fields induced in a magnetic material due to the interaction between light and the spin system of the magnetic material. The contributions of various magneto-optical effects (both standard Faraday or Cotton-Mouton (Voigt) effects and specific L-dependent effects for AFM) are considered as characteristic contributions to the effective field within the sigma model. The most typical experimental data for real AFM are discussed. © 2014 AIP Publishing LLC.

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