The surface tension of magnetic domain walls is one of the major forces that governs micromagnetism and prevents a spontaneous nucleation of magnetic topological defects like nanodomains and skyrmions. With the advent of magnetoelectric and multiferroic materials the problem of the magnetic topological defects stability should be revisited as the magnetic domain walls in the electric field acquire the effective negative surface energy. This additional micromagnetic energy term facilitates the electric‐field induced nucleation of the magnetic topological defect. In the present paper the experimental and theoretical studies reveal the mechanism of electric‐field blowing of the magnetic bubble domain: the electric field suppresses the energy barrier of the magnetic inhomogeneity nucleation and then pulls the opposite domain walls away from each other, thus inflating the bubble.
In recent years, we have been witnessing the intensive development of optical gas sensors. Thin palladium and platinum films as well as tungsten trioxide films with palladium or platinum catalysts are widely used for hydrogen detection, and the optical constants of these materials are required for sensor development. We report the optical parameters retrieved from a set of ellipsometric and transmission spectra for electron-beam evaporated palladium, platinum, and tungsten trioxide films. The tungsten trioxide films were 81 nm, 162 nm, and 515 nm thick and the metal films were as thin as 5–7 nm. Ultrathin palladium and platinum films were shown to be successfully described by local and isotropic permittivity, which is quite different from known bulk values. However, this permittivity showed a strong dependence on adjacent materials, thus illustrating that the ultrathin metallic films can be considered composites characterized by effective permittivity. With the obtained refractive indices and permittivities, the optical spectra of fabricated WO3/Pd and WO3/Pt nanostructures incorporating 1D grating of Al2O3 were in an excellent agreement with the calculated ones without requiring any additional fitting procedures or inclusion of surface roughness layers in numerical models.
We propose a method for determining complex dielectric permittivity dynamics in the gasochromic oxides in the course of their interaction with a gas as well as for estimating the diffusion coefficient into a gasochromic oxide layer. The method is based on analysis of a time evolution of reflection spectra measured in the Kretschmann configuration. The method is demonstrated with a hydrogen-sensitive trilayer including an Au plasmonic film, WO3 gasochromic oxide layer, and Pt catalyst. Angular dependences of the reflectance as well as transmission spectra of the trilayer were measured in series at a constant flow of gas mixtures with hydrogen concentrations in a range of 0–0.36%, and a detection limit below 40 ppm (0.004%) of H2 was demonstrated. Response times to hydrogen were found in different ways. We show that the dielectric permittivity dynamics of WO3 must be retrieved in order to correctly evaluate the response time, whereas a direct evaluation from intensity changes for chosen wavelengths may have a high discrepancy. The proposed method gives insight into the optical properties dynamics for sensing elements based on gasochromic nanostructures.
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