arXiv subjects

D. O. Ignatyeva

Publications and source records attributed to D. O. Ignatyeva.

13 recordsLinked to original sources

arXiv2026

Degeneracy and trajectory control of spin eigenmodes excited by fs-optical pulses in a nearly compensated ferrimagnet

We investigate optically excited spin dynamics in a uniaxial ferrimagnet near the magnetization compensation point under a magnetic field applied along the magnetic anisotropy axis. Experiment and numerical modeling reveal an unusual regime where the frequencies of two spin eigenmodes approach each other and become highly field sensitive. The modes, corresponding to opposite rotations of the Neel vector, simultaneously reverse their handedness at a critical field where their frequencies become degenerate. At this point, the two-frequency precessional dynamics collapses into a linear oscillations directed along the inverse-Faraday-effect excitation induced by a single pump pulse. We further show that a double-pulse excitation scheme enables control of the spin trajectory. These results uncover an unconventional dynamical regime in ferrimagnets and establish new opportunities for manipulating spin motion in magnonic systems and devices.

cond-mat.mtrl-sci↗

arXiv2026

Enhanced magneto-optical intensity effect in a helicity-preserving all-dielectric metasurface at Mie resonances and the anapole state

Nanophotonic structures provide an efficient route to enhancing magneto-optical effects by concentrating electromagnetic fields at subwavelength scales. In this work, we propose and experimentally demonstrate a helicity-preserving all-dielectric metasurface for enhancing magnetization-induced transmission modulation under circularly polarized excitation. The optical response of the structure is governed by the Mie resonances of silicon nanodisks and by a spectral feature associated with the anapole state. In the spectral regions of the Mie resonances, the metasurface exhibits a pronounced enhancement of the magneto-optical intensity response relative to a bare magnetic film of the same thickness, with the normalized magneto-optical intensity effect increased by a factor of about 2-3. A strong response is also observed in the spectral region associated with the anapole state, manifested as a local transmission maximum. In this regime, the normalized magneto-optical intensity effect exceeds that of the bare magnetic film by about 30%, while the metasurface transmission remains as high as around 80%. The enhanced response in this spectral region is preserved over a broad range of incidence angles. These results demonstrate that all-dielectric metasurfaces combining Mie resonances with the spectral feature associated with the anapole state provide an efficient platform for magneto-optical intensity modulation of circularly polarized light at high transmission.

physics.optics↗

arXiv2026

The prospects of nonthermal magnetization switching in near-compensated rare earth iron garnets

Ultrafast spin dynamics in a magnetically compensated rare earth iron garnet film driven by femtosecond optical pulses through the inverse Faraday effect is theoretically investigated. Numerical simulations based on the equations of motion for the Néel vector reveal the temporal evolution of the system and its trajectories in the effective potential landscape tuned by external field and temperature. The results demonstrate a clear threshold behavior: weak pulses induce only oscillations around the initial equilibrium state, while a stronger excitation results in a deterministic magnetization switching. The switching threshold is determined by the magnetic state of the sample on its phase diagramme as well as on the laser pulse helicity. This mechanism demonstrates a non-thermal and even non-absorptive pathway towards optomagnonic logic and memory devices.

cond-mat.mtrl-sci↗

arXiv2025

Unusual sign-changing Faraday effect in nanometer-thick magnetic films

It is generally believed that the magneto-optical Faraday effect appears in the the bulk of a magnetic material and its sign is fully determined by the sign of the non-diagonal permittivity element. Here we reveal an additional contribution to the Faraday effect from the film interfaces. It becomes notable for films with a thickness of a few tens of nanometers. As a result, in the absorption band of the film a novel feature of the Faraday effect is experimentally observed and numerically confirmed: sign of the Faraday rotation at a fixed wavelength becomes dependent on the film thickness and therefore is ambiguously related to the sign of the gyration and magnetization of the film. We elaborated an analytical model taking into account an interplay between the bulk and surface contributions which nicely describes the experimental data. Moreover, the Faraday rotation coming purely from interfaces without any bulk contribution is demonstrated. Possible applications of the observed unusual Faraday rotation behavior include hardware data encryption and other devices performing polarization control at nanoscale.

physics.optics↗

arXiv2025

Thermally-controlled magnetooptical metasurface for tunable Faraday rotation

We present novel type of tunable magneto-optical metasurfaces performing Faraday rotation, the sign and value of which are not fixed after the structure fabrication but can be tuned in a wide range via heating of the metasurface. We demonstrate both experimentally and theoretically that the Faraday rotation angle is enhanced in the vicinity of the magnetodipole and electrodipole Mie resonances and can be changed in a wide range from -0.3 degrees to +0.1 degrees for the same metasurface at fixed wavelength of incident light under the temperature changes from the 294~K to 488~K. Such thermal heating can be performed by an external control laser. As laser radiation can be focused at the spots of $~\sim 1μ$m diameter, the magneto-optical response can also be tuned locally. Thus one may obtain the inhomogeneous magnetooptically-induced polarization rotation distributions across the metasurface by the creation of the laser beam patterns with the desired intensity profiles. Another possibility opened by the proposed merasurface is self-modulation of polarization of laser light performed depending on its intensity.

physics.optics↗

arXiv2024

Asymmetric Faraday effect caused by a break of spatial symmetry

It is widely known that the magneto-optical Faraday effect is linear in magnetization, and therefore the Faraday angles for the states with opposite magnetizations are of opposite sign but equal in modulus. Here we demonstrate that under certain spatial symmetry-breaking conditions, an asymmetric Faraday effect (AFE) arises, meaning that the Faraday angles for opposite magnetic states differ not only in sign but in absolute value as well. Experimental investigations of AFE are performed in a one-dimensional all-garnet magnetophotonic crystal, where AFE appears in the vicinity of the cavity resonance for an oblique incidence of light with an inclined light polarization plane. The magnitude of the observed asymmetry between Faraday rotations for the two opposite magnetizations is very large and reaches 30$\%$ of the absolute value of the Faraday effect. We confirm the generality of the suggested effect by the numerical analysis of several different configurations in which AFE arises. The discovered AFE is of prime importance for nanoscale magnonics and optomagnetism.

physics.optics↗

arXiv2023

Unconventional spin dynamics in the non-collinear phase of a ferrimagnet

Ferrimagnets containing several partially compensated magnetic sublattices are considered the most promising materials for all-optical data storage and for ultrafast communications based on spin waves. There are two magnetic phases of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics in ferrimagnets has been studied mostly in the collinear state without paying much attention to the kind of the magnetic phase. Here we investigate laser induced ultrafast spin dynamics in a rare-earth iron garnet film in the noncollinear phase as well. We identify a crucial influence of the magnetic phase on the excited spin modes which allowed us to discover several prominent effects previously overlooked. In particular, the non-collinearity makes the quasi-antiferromagnetic mode sensitive to the external magnetic field and brings its frequency close to the frequency of the quasiferromagnetic mode. The latter maximizes near the magnetization compensation point and vanishes towards the collinear phase. Spectacularly, at the phase transition the quasiferromagnetic mode becomes soft and its amplitude significantly increases reaching 7°. This opens new opportunities for the ultrafast control of spins in ferrimagnets for nonthermal data storage and data processing.

cond-mat.mtrl-sci↗

arXiv2022

Birefringence-mediated enhancement of the magneto-optical activity in anisotropic magnetic crystals

Optical anisotropy is usually treated as an unfavorable condition for the magneto-optical measurements since it is known to diminish the Faraday rotation concerning the case of the isotropic medium. Here we show that the situation could be quite opposite: a phenomenon of birefringence mediated enhancement of the magneto-optical activity appears if the incident light polarization and angle of incidence are set properly. The present study relies on the experimental, analytical, and numerical studies of iron borate $\mathrm{FeBO_3}$ crystals. We demonstrate a significant increase of the magneto-optical activity resulting in nearly $100\%$ magneto-optical light modulation magnitude. The approach applies to other types of birefringent crystals with the magneto-optical response that makes it crucial for various practical applications, including magneto-optical microscopy, pump-probe studies, and others.

physics.optics↗

arXiv2021

Optical excitation and probing of the antiferromagnetic modes with non-uniform in-depth distribution in birefringent antiferromagnetic crystals

Optical pump-probe setups are commonly used for excitation and investigation of the spin dynamics in various types of magnetic materials. However, usually the spatially homogeneous excitation is considered. In the present study we describe an approach for optical excitation of the nonuniform THz spin dynamics and for probing its spatial distribution inside a magnetic crystal. We propose to illuminate a crystal with laser pulses of properly adjusted polarization to benefit from a strong optical birefringence inherent to the crystal. It results in an unusual behavior of the effective magnetic field generated by the pulses due to the inverse Faraday effect and the peculiar sign-changing dependence of the direct Faraday effect inside the crystal. The study is performed exemplary for yttrium orthoferrite crystal although the proposed approach is applicable for various magnetic materials with optical anisotropy.

physics.optics↗

arXiv2020

Nanophotonic structures with optical surface modes for tunable spin current generation

Heat generated by spin currents in spintronics-based devices is typically much less than that generated by charge current flows in conventional electronic devices. However, the conventional approaches for excitation of spin currents based on spin-pumping and spin Hall effect are limited in efficiency which restricts their application for viable spintronic devices. We propose a novel type of photonic-crystal (PC) based structures for efficient and tunable optically-induced spin current generation via the Spin Seebeck and inverse spin Hall effects. It is experimentally demonstrated that optical surface modes localized at the PC surface covered by ferromagnetic layer and materials with giant spin-orbit coupling (SOC) notably increase the efficiency of the optically-induced spin current generation and provides its tunability by modifying light wavelength or angle of incidence. Up to 100% of the incident light power can be transferred to heat within the SOC layer and, therefore, to spin current. Importantly, high efficiency becomes accessible even for ultra-thin SOC layers. Moreover, surface patterning of the PC-based spintronic nanostructure allows local generation of spin currents at the pattern scales rather than diameter of the laser beam.

cond-mat.mes-hall↗

arXiv2020

Layer-Selective Magnetization Switching in the Chirped Photonic Crystal with GdFeCo

Here we propose a magnetophotonic structure for the layer-selective magnetization switching with ultrashort laser pulses of different wavelengths. It is based on a chirped magnetophotonic crystal (MPC) containing magnetic GdFeCo and nonmagnetic dielectric layers. At each operating wavelength the laser pulses heat up to necessary level only one GdFeCo layer that leads to its magnetization reversal without any impact on the magnetization of the other layers. Moreover, magneto-optical reading of the MPC magnetization state is discussed. Lateral dimensions of the considered MPC can be made small enough to operate as a unit cell for data storage.

physics.optics↗

arXiv2020

Vector magneto-optical magnetometer based on the resonant all-dielectric gratings with highly anisotropic iron-garnet films

A sensitive vector magnetometry with high spatial resolution is important for various practical applications, such as magnetocardiography, magnetoencephalography, explosive materials detection and many others. We propose a magnetometer based on the magnetic iron-garnet film possessing a very high magnetic anisotropy, placed in the rotating external magnetic field. Each of the measured magnetic field spatial components produces different temporal harmonics in the out-of-plane magnetization dependence. The dielectric resonant grating placed on the top of an ultrathin film enhanced the magneto-optical response 10 times which makes it possible to achieve 10 times higher spatial resolution in the perpendicular to the film direction. The reported magneto-optical magnetometer allows one to measure simultaneously all three spatial components of the magnetic field with high spatial resolution and sensitivity up to 100 pT/Hz$^{1/2}$.

physics.app-ph↗

arXiv2019

High-Q surface electromagnetic wave resonance excitation in magneto-photonic crystals for super-sensitive detection of weak light absorption in near-IR

Mid-infrared spectrum can be recorded from almost any material making the mid-infrared spectroscopy an extremely important and widely used sample characterization and analytical technique. However, sensitivity photoconductive detectors operate primarily in the near-infrared (NIR) but not in the mid-infrared making the NIR more favorable for accurate spectral analysis. Although absorption cross-section of vibrational modes in near-infrared is orders of magnitude smaller compared to the fundamental vibrations in mid-infrared, different concepts were proposed to increase the detectability of weak molecular transitions overtones. Yet, the contribution of magneto-photonic structures in near-infrared absorption effect has never been explored so far. Here we propose high-Q magneto-photonic structures for a super-sensitive detection of weak absorption resonances in near-infrared. We analyze the contributions of both magnetic and non-magnetic photonic crystal (PC) configurations to the detection of weak molecular transitions overtones. Our results constitute an important step towards development of highly sensitive spectroscopic tools based on high-Q magneto-photonic sensors.

physics.optics↗