Contents
Section 1. Topics on theoretical electrodynamics
Spin-flop transition in nickel oxide and similar easy-plane antiferromagnets
A.V. Rozhkov
Abstract
We theoretically investigate the spin-flop transition in easy-axis antiferromagnets, with particular emphasis on nickel oxide and related materials. Using a simple phenomenological energy function that incorporates hexagonal anisotropy within the easy magnetization plane, we analyze the behavior of the antiferromagnetic state in the presence of an external magnetic field. It is demonstrated that a magnetic field applied parallel to the easy plane can induce a spin-flop transition, as long as the field is collinear with one of the easy axes within the easy plane. This finding is complementary to a more conventional situation of a spin-flop transition in easy-axis antiferromagnets placed in magnetic field applied along their easy axis. In contrast to the first-order transition in easy-axis materials, the transition in easy-plane systems is shown to be of second order. It is accompanied by a discontinuity in the differential magnetic susceptibility. The latter may serve a clear experimental signature of the spin flop. We compare our theoretical predictions with available experimental magnetometry data and find that the data partially support our conclusions. Furthermore, we show that the proposed theoretical framework can be used to extract key parameters of the antiferromagnetic state, including anisotropy constants and exchange fields, directly from magnetometry measurements. These results extend the understanding of field-induced phase transitions in antiferromagnets and may be relevant for the interpretation of magnetic response data in a broad class of easy-plane antiferromagnetic materials.
Keywords: oxide, NiO, spin-flop transition, easy plane antiferromagnet, susceptibility
Section 2. Topics on interaction of an electromagnetic field with materials
Retrieving parameters of functional structure for optical sensor
D.K. Vysokikh, A.S. Amiraslanov, E.V. Sergeev, K.A. Buzaverov, D.P. Kulikova, A.V. Shelaev, A.V. Baryshev, A.S. Baburin, I.A. Rodionov, A.V. Dorofeenko
Abstract
We examine a planar dielectric lattice consisting of the quartz substrate / thin layer of tungsten trioxide / lattice of quartz strips / ultrathin palladium film. The measurement results of the optical transmission spectrum are compared with the calculated results. Agreement with the experimental data is achieved by adjusting the geometry of the structure, as well as adding bulk absorption and surface scattering on the roughness of the structure, modeled by losses in the tungsten trioxide layer and addition to the imaginary part of the dielectric constant of palladium proportional to the frequency third power (surface absorption), respectively. Both the experimental and calculated spectra were approximated using a superposition of the polynomial background and two Lorentz resonances. The equality of the parameters of the approximation functions, the most important of which are the width, depth and position of the resonant peaks, as well as the average level of the non-resonant part of the spectrum, was considered as a criterion for matching the model to the measured data. Most parameters match with an accuracy exceeding 10 %. Moreover, a step-by-step analysis of various factors affecting the type of transmission coefficient spectrum is carried out, the specific features of the spectrum are compared with the changes in the numerical model that lead to their appearance.
Keywords: optical characterization, transmittance spectrum, planar optical structure, diffraction grating, scattering by the optical surface
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