arXiv subjects

Ivan Soldatov

Publications and source records attributed to Ivan Soldatov.

8 recordsLinked to original sources

arXiv2026

Sculpting Spin-Wave Landscapes via Curvature of 2D Magnonic Crystals

Engineering the dispersion relation is one of the key ingredients enabling the application of spin waves in computational elements. One way to engineer the spin-wave band structure is to create an artificial magnonic crystal, which can be used to design specific band gaps or dispersion branches. However, creating a two-dimensional magnonic crystal usually requires removing material, which dramatically decreases the decay lengths of spin waves. Here, we present a method to manipulate the demagnetizing field landscape by utilizing large-area curvilinear nanotemplates consisting of three-dimensional nanopyramids arranged in a square lattice with a period of 400 nm. In a 50-nm-thick Permalloy film grown on these curvilinear templates, we experimentally observe a complete in-plane band gap together with flat-band modes that exhibit strong real-space localization of the spin waves in the pyramid valleys. Micro-focused Brillouin light scattering measurements corroborate the numerically predicted dispersion and reveal the possibility of opening and closing this gap by varying the external magnetic field. Our results establish three-dimensional-templated continuous films as a versatile platform for two-dimensional signal processing and magnonic computing elements.

cond-mat.mes-hall↗

arXiv2024

Spatial mapping of magnetization fluctuations via time-lapse Kerr microscopy

Combining wide-field magneto-optical Kerr microscopy with a time-lapse analysis scheme allows investigating magnetization fluctuations with high spatial as well as temporal resolution. We here use this technique to study magnetization fluctuations in a thin ferromagnetic film prepared into a quasi-equilibrium magnetic state via a dedicated field sweep protocol. Our experiments reveal spatially localized noise hotspots distributed across the sample surface within the magnetic domains in the quasi-equilibrium state. The spatial density of the noise hot spots is very similar at different low magnetic field strengths, as expected from the fluctuation-dissipation theorem. The measurement scheme thus opens the way for the spatially resolved investigation of quasi-equilibrium noise processes in magnetic materials.

cond-mat.mes-hall↗

arXiv2024

Transition from ferromagnetic to noncollinear to paramagnetic state with increasing Ru concentration in FeRu films

The structural and magnetic properties of sputter-deposited Fe$_{100-x}$Ru$_x$ films were studied for $x \leq 50$. The crystal structure of Fe$_{100-x}$Ru$_x$ is shown to be predominantly body-centered cubic for $x<13$ and to undergo a gradual transition to hexagonal close-packed in the concentration range $13 \lesssim x \lesssim 20$. Magnetic measurements indicate that the addition of Ru induces a noncollinear magnetic order in the body-centered cubic FeRu alloys, while the hexagonal close-packed FeRu alloys exhibit paramagnetic behavior. Increasing the Ru concentration in body-centered cubic FeRu alloys decreases the size of magnetic domains, approaching the size of magnetic grains. A simple atomistic model was used to show that antiferromagnetic coupling of Fe atoms across Ru atoms can be responsible for inducing noncollinear order in the FeRu cubic structures. Magnetic multilayer structures used in thin-film magnetic devices make extensive use of both Fe and Ru layers. Our results reveal that the presence of even a small amount of Ru in Fe influences the magnetic order of Fe, which could impact the performance of these devices.

cond-mat.mtrl-sci↗

arXiv2024

Single-crystalline YIG flakes with uniaxial in-plane anisotropy and diverse crystallographic orientations

We study Y3Fe5O12 (YIG) flakes that we produce via mechanical cleaving and exfoliation of YIG single crystals. By characterizing their structural and magnetic properties, we find that these YIG nanoflakes have surfaces oriented along unusual crystallographic axes and uniaxial in-plane magnetic anisotropy due to their shape, both of which are not commonly available in YIG thin films. These physical properties, combined with the possibility of picking up the YIG flakes and stacking them onto flakes of other van der Waals materials or pre-patterned electrodes or waveguides, open unexplored possibilities for magnonics and for the realization of novel YIG-based heterostructures and devices.

cond-mat.mtrl-sci↗

arXiv2023

Antiskyrmions and their electrical footprint in crystalline mesoscale structures of Mn$_{1.4}$PtSn

Skyrmionic materials hold the potential for future information technologies, such as racetrack memories. Key to that advancement are systems that exhibit high tunability and scalability, with stored information being easy to read and write by means of all-electrical techniques. Topological magnetic excitations such as skyrmions and antiskyrmions, give rise to a characteristic topological Hall effect. However, the electrical detection of antiskyrmions, in both thin films and bulk samples has been challenging to date. Here, we apply magneto-optical microscopy combined with electrical transport to explore the antiskyrmion phase as it emerges in crystalline mesoscale structures of the Heusler magnet Mn$_{1.4}$PtSn. We reveal the Hall signature of antiskyrmions in line with our theoretical model, comprising anomalous and topological components. We examine its dependence on the vertical device thickness, field orientation, and temperature. Our atomistic simulations and experimental anisotropy studies demonstrate the link between antiskyrmions and a complex magnetism that consists of competing ferromagnetic, antiferromagnetic, and chiral exchange interactions, not captured by micromagnetic simulations.

cond-mat.mtrl-sci↗

arXiv2023

Modification of three-magnon splitting in a flexed magnetic vortex

We present an experimental and numerical study of three-magnon splitting in a micrometer-sized magnetic disk with the vortex state strongly deformed by static in-plane magnetic fields. Excited with a large enough power at frequency $f_\mathrm{RF}$, the primary radial magnon modes of a cylindrical magnetic vortex can decay into secondary azimuthal modes via spontaneous three-magnon splitting. This nonlinear process exhibits selection rules leading to well-defined and distinct frequencies $f_\mathrm{RF}/2\pm Δf$ of the secondary modes. Here, we demonstrate that three-magnon splitting in vortices can be significantly modified by deforming the magnetic vortex with in-plane magnetic fields, leading to a much richer three-magnon response. We find that, with increasing field, an additional class of secondary modes is excited which are localized to the highly-flexed regions adjacent to the displaced vortex core. While these modes satisfy the same selection rules of three-magnon splitting, they exhibit a much lower three-magnon threshold power compared to regular secondary modes of a centered vortex. The applied static magnetic fields are small ($\simeq$ 10 mT), providing an effective parameter to control the nonlinear spectral response of confined vortices. Our work expands the understanding of nonlinear magnon dynamics in vortices and advertises these for potential neuromorphic applications based on magnons.

cond-mat.mes-hall↗

arXiv2020

Topological Hall effect arising from the mesoscopic and microscopic non-coplanar magnetic structure in MnBi

The topological Hall effect (THE), induced by the Berry curvature, which originates from non-zero scalar spin chirality, is an important feature for mesoscopic topological structures, such as skyrmions. However, the THE might also arise from other microscopic non-coplanar spin structures in the lattice. Thus, the origin of the THE inevitably needs to be determined to fully understand skyrmions and find new host materials. Here, we examine the Hall effect in both bulk- and micron-sized lamellar samples of MnBi. The sample size affects the temperature and field range in which the THE is detectable. Although bulk sample exhibits the THE only upon exposure to weak fields in the easy-cone state, in thin lamella the THE exists across a wide temperature range and occurs at fields near saturation. Our results show that both the non-coplanar spin structure in the lattice and topologically non-trivial skyrmion bubbles are responsible for the THE, and that the dominant mechanism depends on the sample size. Hence, the magnetic phase diagram for MnBi is strongly size-dependent. Our study provides an example in which the THE is simultaneously induced by two mechanisms, and builds a bridge between mesoscopic and microscopic magnetic structures.

cond-mat.mes-hall↗

arXiv2016

Selective sensitivity in Kerr microscopy

A new technique for contrast separation in wide-field magneto-optical Kerr microscopy is introduced. Utilizing the light from eight light emitting diodes, guided to the microscope by glass fibers and being switched synchronously with the camera exposure, domain images with orthogonal in-plane sensitivity can be displayed simultaneously at real-time and images with pure in-plane or polar contrast can be obtained. The benefit of this new method of contrast separation is demonstrated for permalloy films, a NdFeB sinter magnet, and a cobalt crystal. Moreover, the new technique is shown to strongly enhance the sensitivity of Kerr microscopy by eliminating parasitic contrast contributions occurring in conventional setups. A doubling of the in-plane domain contrast and a sensitivity to Kerr rotations as low as 0.6~mdeg is demonstrated

physics.ins-det↗