Alexey V. Ognev

• Professor
• Professor at Far Eastern Federal University

The phenomenon of shape anisotropy predominantly constitutes the principal factor influencing effective anisotropy, serving as a significant determinant of the magnetic characteristics of one-dimensional ferromagnetic nanostructures, materials that hold substantial promise for a diverse array of applications in the domains of electronics and biomed...

The development of spintronic emitters of broadband THz pulses relies on designing heterostructures where processes of laser-driven spin current generation and subsequent spin-to-charge current conversion are the most efficient. An interface between ferromagnetic and nonmagnetic layers in the emitter is one of the critical elements. Here, we study...

The utilization of ferrimagnets in spintronic applications purportedly offers the potential for high-speed and energy-efficient switching of magnetic states, coupled with their notable stability. This collection of characteristics is commonly observed in ferrimagnetic materials that are in close proximity to states of magnetic or angular momentum c...

The potential to produce nanostructures with intricate shapes in large quantities holds promise for a range of applications in the fields of nanoelectronics and biomedicine. Here a method for fabricating jellyfish‐like Ni nanowires (JFNWs) using bilayered nanoporous anodic alumina templates with through pores of varying diameters in each layer is p...

The T-type CoFeB/spacer/CoFeB structure is a promising candidate for the development of perpendicular spin–orbit torque (SOT) magnetic random-access memory and other SOT devices. It consists of an in-plane magnetized layer, a perpendicularly magnetized layer, and a non-magnetic metal spacer that induces interlayer exchange coupling. By engineering...

Multilayered metallic nanostructures are promising for the fabrication of spin valves based on the giant magnetoresistive effect and for studies of the nature of topological magnetism, aimed at the development of new nanoscale data storage and transfer devices, e.g. those based on magnetic skyrmions. It is still an important task to develop methods...

The development of telecommunication technologies has increased the relevance of remote-control tasks, including the use of methods of increased accuracy for critical areas. Depending on the application field, remote control or monitoring devices can be equipped with various types of sensors, including inertial measurement units (IMU). By combining...

In this work we demonstrate the fabrication protocol of 2D-magnetoplasmonic crystals consisting of permalloy column arrays. Dependences of morphological, magnetic, optical, and magneto-optical properties of 2D-magnetoplasmonic crystals on the e-beam exposition dose are studied. Proposed protocol is suitable for the fabrication of 2D-structures with...

The study of magnetic films grown on the oxidized silicon surface is of interest from the point of view of creating ” ferromagnetic metal/dielectric“ tunnel contacts and implementing the transport of spin-polarized electrons. In this work, textured polycrystalline magnetite films were prepared by reactive deposition of iron onto a SiO2/Si(001) surf...

Multilayer metallic nanostructures are promising not only for the creation of spin valves based on the giant magnetoresistance effect, but also for studying the nature of topological magnetism aiming to creation, for example, new nanoscale devices for storing and transmitting data based on magnetic skyrmions. Actual problem remains the development...

Magnetic nanoparticles with capacity for surface functionalisation have potential applications in water purification and biomedicine. Here, a simple co-precipitation technique was used to synthesize mesoporous ferrite nanoparticles in the presence of cetyltrimethylammonium bromide (CTAB) micellular surfactant. The as-synthesized ferrite nanoparticl...

Nano- and microstructures based on ferrimagnets can demonstrate high efficiency and dynamics of current-induced magnetization switching combined with high stability of spin textures such as bubble domains and skyrmions, which are of practical importance for the development of spintronics and spin-orbitronics. This set of features is usually associa...

High phase and structural sensitivity of magnetic properties strongly impacts the fabrication quality of the permanent magnets, therefore revealing effects of synthesis conditions on physico-chemical characteristics of magnetic materials is of paramount importance for optimization of magnet production especially in case when non-conventional techni...

The possibility of effective solidification of spent sorbents containing radioactive cesium by spark plasma sintering (SPS) technology for their safe and long-term disposal was studied. The kinetics of consolidation spent sorbent based on magnetic zeolite after adsorption saturation with cesium (∼23 wt. %) under SPS conditions in the range of 700–9...

Neodymium-iron-boron magnetic oxide powders synthesized by sol–gel Pechini method were studied by using X-ray photoelectron spectroscopy (XPS) and quantum chemical modeling. The powder structure was examined by using X-ray diffraction (XRD) and modeled by using density functional theory (DFT) approximation. The electronic structures of the core and...

Recently, an ultimate diode effect, a superconducting diode where an electric current shows the superconducting state in one direction and the normal state in the other direction, has been discovered in a noncentrosymmetric Nb/V/Ta superlattice. Here, we report that the polarity of the superconducting diode shows a sign reversal as a magnetic field...

Magnetic Memory Cells The dense packing of magnetic memory cells under the influence of magnetostatic fields can change the overall ability of the device to store information. In article number 2203555, Young Keun Kim, Alexander S. Samardak, and co‐workers consider 3D magnetic geometry by employing Fe/Au barcode nanowire arrays. Complex magnetostat...

Metallic barcode nanowires (BNWs) composed of repeating heterogeneous segments fabricated by template‐assisted electrodeposition can offer extended functionality in magnetic, electrical, mechanical, and biomedical applications. The authors consider such nanostructures as a 3D system of magnetically interacting elements with magnetic behavior strong...

Metallic barcode nanowires (BNWs) composed of repeating heterogeneous segments fabricated by template-assisted electrodeposition can offer extended functionality in magnetic, electrical, mechanical, and biomedical applications. We can consider such nanostructures as a three-dimensional system of magnetically interacting elements with magnetic behav...

Tuning magnetic properties of perpendicularly magnetized system is technologically important and have application in modern spintronics devices. In this article, we have considered TbFe based perpendicular trilayer magnetic system by inserting a nonmagnetic spacer layer in between. A systematic variation in thickness of non-magnetic Ti spacer (S) i...

The Dzyaloshinskii–Moriya interaction (DMI) is an antisymmetric exchange in magnetic structures with broken inversion symmetry. In magnetic heterostructures, the bulk DMI may co-exist with the conventional interfacial DMI contributing to the chiral magnetic behavior of the system. Here, we report the enhancement of DMI in Pt/Co heterostructures whe...

The diode effect is fundamental to electronic devices and is widely used in rectifiers and a.c.–d.c. converters. At low temperatures, however, conventional semiconductor diodes possess a high resistivity, which yields energy loss and heating during operation. The superconducting diode effect (SDE)1–8, which relies on broken inversion symmetry in a...

This paper focuses on the investigation of magnetic properties of Ni nanowire arrays synthesized using Al 2 O 3 porous templates with different durations of first anodization. It has been shown that the diameter of the pores in the template is increasing with an increase in the first anodization time up to 2 hours, and the interpore distance become...

Perpendicularly magnetized structures that are switchable using a spin current under field-free conditions can potentially be applied in spin-orbit torque magnetic random-access memory (SOT-MRAM). Several structures have been developed; however, new structures with a simple stack structure and MRAM compatibility are urgently needed. Herein, a typic...

Technological conditions under which a two-phase epitaxial thin film of Co is formed on a stepped surface of Si(111)-5.55×5.55-Cu with a buffer layer of Cu(111) and an ordered array of single-crystal nanostrips of hcp-Co with sharp interphase boundaries growing by self-organization were determined. The crystal structure of epitaxial thin films and...

Hard magnetic Nd-(Fe,Co)-B powders prepared by ball milling from melt-spun ribbons are investigated. The effect of doping by 1 wt% Cu on magnetic properties is shown. Furthermore, the thermal stability of the Nd-(Fe,Co)-B powder with Cu doping is studied. The structure and morphology of the powders are observed. The contribution of the Nd2(Fe, Co)1...

The diode effect is fundamental to electronic devices and is widely used in rectifiers and AC-DC converters. At low temperatures, however, conventional semiconductor diodes possess a high resistivity, which yields energy loss and heating during operation. The superconducting diode effect (SDE), which relies on broken inversion symmetry in a superco...

Perpendicularly magnetized structures that are switchable using a spin current under field-free conditions can potentially be applied in spin-orbit torque magnetic random-access memory (SOT-MRAM). Several structures have been developed; however, new structures with a simple stack structure and MRAM compatibility are urgently needed. Herein, a typic...

Understanding the nature of recently discovered spin-orbital induced phenomena and a definition of a general approach for "ferromagnet/heavy-metal" layered systems to enhance and manipulate spin-orbit coupling, spin-orbit torque, and the Dzyaloshinskii-Moriya interaction (DMI) assisted by atomic-scale interface engineering are essential for develop...

Deterministic magnetization switching driven by current-induced spin–orbit torque (SOT) without an external magnetic field has potential applications in magnetic random access memory. Here, we realized the field-free magnetization switching in a T-type structure (CoFeB/W/CoFeB), where the two CoFeB layers have perpendicular magnetic anisotropy and...

In this work, we examine the temperature dependence of magnetic domain wall (DW) creep motion in ferrimagnetic Tb/CoFeB/MgO microwires by using a real-time DW detection method. By measuring the field-dependent DW velocity at various temperatures, the creep-scaling constant and the characteristic velocity were evaluated from the creep-scaling analys...

The paper describes the method for producing WC-10wt%Co hard alloy with 99.6% of the theoretical density and a Vickers hardness of ~1400 HV 0.5. Experimental data on densification dynamics, phase composition, morphology, mechanical properties, and grain size distribution of WC-10%wtCo using spark plasma sintering (SPS) within the range of 1000–1200...

The fabrication approach of a magnonic crystal with a step-like hysteresis behavior based on a uniform non-monotonous iron layer made by shadow deposition on a preconfigured substrate is reported. The origin of the step-like hysteresis loop behavior is studied with local and integral magnetometry methods, including First-Order Reversal Curves (FORC...

Spark Plasma Sintering (SPS), also known as pulsed electric current sintering (PECS) or field assisted sintering technology (FAST), belongs to a class of powder metallurgy methods. Investigations of the effect of thermal, electric and electromagnetic fields arising under the conditions of spark plasma sintering of ceramic materials on their final c...

In conventional Kerr and Faraday microscopy, the sample is illuminated with plane-polarized light, and a magnetic domain contrast is generated by an analyzer making use of the Kerr or Faraday rotation. Here, we demonstrate possibilities of analyzer-free magneto-optical microscopy based on magnetization-dependent intensity modulations of the light....

This work deals with the investigation and optimization of the crystalline phases, magnetic properties, chemical composition and morphology of Nd-(Fe1-xCox)-B oxide magnetic particles (where x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, and 0.5) synthesized by Pechini method that can be used as a precursor for the production of Nd2(Fe,Co)14B hard magnetic...

In conventional Kerr- and Faraday microscopy the sample is illuminated with plane-polarised light and a magnetic domain contrast is generated by an analyser making use of the Kerr- or Faraday rotation. In this paper we demonstrate possibilities of analyser-free magneto-optical microscopy based on magnetisation-dependent intensity modulations of the...

We show that a trilayer magnetic structure, consisting of a heavy metal (Platinum) as a buffer, an ultrathin ferromagnet (Cobalt) as a functional layer, and an antiferromagnetic insulator (Nickel oxide, NixOy) as a capping, is a host of intriguing physical phenomena desirable for spintronics. X-ray photoelectron spectroscopy revealed changes in the...

Gradual magnetization switching driven by spin–orbit torque (SOT) is preferred for neuromorphic computing in a spintronic manner. Here we have applied focused ion beam to selectively illuminate patterned regions in a Pt/Co/MgO strip with perpendicular magnetic anisotropy, soften the illuminated areas, and realize the gradual switching by a SOT-driv...

To stabilize nontrivial spin textures, e.g., skyrmions or chiral domain walls in ultrathin magnetic films, an additional degree of freedom, such as the interfacial Dzyaloshinskii–Moriya interaction (IDMI), must be induced by the strong spin-orbit coupling (SOC) of a stacked heavy metal layer. However, advanced approaches to simultaneously control t...

Magnetic skyrmions are stable spin textures with quasi-particle behavior and attract significant interest in fundamental and applied physics. The metastability of magnetic skyrmions at zero magnetic field is particularly important to enable, for instance, a skyrmion racetrack memory. Here, the results of the nucleation of stable skyrmions and forma...

Nanoparticles of Nd(Fe1-xCox)B with Co concentrations ranging from x = 0 to 0.5 were prepared using a modified Pechini-type sol-gel method. We have shown the influence of Co on the morphology and size of nanoparticles, as well as on elements distribution in nanostructures. It was found that nanoparticles with increased content of Fe and Co were for...

Continuous switching driven by spin-orbit torque (SOT) is preferred to realize neuromorphic computing in a spintronic manner. Here we have applied focused ion beam (FIB) to selectively illuminate patterned regions in a Pt/Co/MgO strip with perpendicular magnetic anisotropy (PMA), soften the illuminated areas and realize the continuous switching by...

The cobalt (Co)–tungsten (W) alloys exhibit unique combinations of mechanical and magnetic properties, biocompatibility, resistance against corrosion, wear, and high-temperature, which makes them desirable materials for various practical applications. A nanoporous template with incorporated Co–W alloy nanowires is a soft magnetic composite, whose d...

The study describes direct precipitation, original template, and additional thermal reduction methods for the synthesis of materials based on cobalt oxides and their composites, promising as magnetic sorbents for the selective extraction and preconcentration of uranium(VI) from aqueous media. The thermal decomposition of intermediates and the phase...

To stabilize the non-trivial spin textures, e.g., skyrmions or chiral domain walls in ultrathin magnetic films, an additional degree of freedom such as the interfacial Dzyaloshinskii-Moriya interaction (IDMI) must be induced by the strong spin-orbit coupling (SOC) of a stacked heavy metal layer. However, advanced approaches to simultaneously contro...

Versatile spin-orbit-torque switching is potentially useful for spin logics and neuromorphic computing. Using two orthogonal spin-orbit torques, we nonvolatilely switch the magnetization of a Pt/Co/MgO crossbar with perpendicular magnetic anisotropy among multistates such as the spin-up, spin-down, and spin-random states. By electrical methods, we...

Magnetoplasmonic crystals consisted of the combination of noble and ferromagnetic thin films deposited on diffraction gratings represent a special class of nanostructures that can utilize the magneto-optical Kerr effect enhanced by surface plasmon-polaritons excitation for the probing of an external DC magnetic field. Optical and magneto-optical pr...

Recent development of the magnetic material engineering led to achievement of the systems with a high interfacial Dzyaloshinskii-Moriya interaction (DMI). As a result, the formation of non-collinear magnetic soliton states or nonreciprocal spin wave dynamics is achievable. Typically used materials are based on bi-layers Heavy Metal/Ferromagnet, e.g...

This paper presents results of the application of Ti/ta-C films to micro drilling operation for machining. Tetrahedral amorphous carbon (ta-C) films were successfully deposited on WC-Co substrates by a filtered cathodic vacuum arc (FCVA) system. The mechanical and flexion properties of Ti/ta-C films were systematically investigated. The experimenta...

The reliable estimation of the spin-orbital-torque (SOT) efficiency in ferromagnetic multilayers with small coercive force is a nontrivial task, but extremely demanded for implementation of current-induced magnetization reversal memory cells. Here, we report on results of an experimental study of current-induced magnetization reversal of the Ru/Co/...

Magnetoresistive (MR) sensors have been identified as promising candidates for the development of high-performance magnetometers due to their high sensitivity, low cost, low power consumption, and small size. The rapid advance of MR sensor technology has opened up a variety of MR sensor applications. These applications are in different areas that r...

We investigate magnetic properties of nickel nanoparticles electrodeposited on TiO 2 nanotubes by different techniques including direct current (DC) and cyclic voltammetry (CV) deposition. TiO 2 nanotubes were fabricated by anodic oxidation from an organic electrolyte under constant voltage on Ti substrates. Using scanning and transmission electron...

Magnetoplasmonic crystals represent a special class of hybrid structures consisting of one-dimensional periodic diffraction grating combined with a ferromagnetic layer. Magnetoplasmonic crystals are functional materials, which can be used for high precision magnetic sensors, given that their magneto-optical activity is enhanced by the plasmon reson...

An experimental study of current-induced magnetization reversal of the Ru/Co/Ru and Ru/Co/Ru/W structures was carried out. In the considered structures, due to the small value of the coercive force comparable in magnitude to the Oersted field and the SOT effect field, magnetization reversal is carried out by moving a domain wall parallel to the dir...

Mesoporous magnetic materials have found interesting potential applications in electrochemical energy harvesting and energy-efficient magnetic actuation device applications. Here we report on the electrodeposition and magnetic properties of mesoporous nickel films from lyotropic liquid crystal (LLC) templates formed by cetyltrimethylammoniumbromide...

The lateral motion of a magnetic skyrmion, arising because of the skyrmion Hall effect, imposes a number of restrictions on the use of this spin state in the racetrack memory. A skyrmionium is a more promising spin texture for memory applications, since it has zero total topological charge and propagates strictly along a nanotrack. Here, the stabil...

Helicity, a natural property of macro-, micro-, and nano-objects, potentially offers a new dimension to mechanical and electromagnetic applications for creating emerging nanodevices, such as nanorobots, nanomagnets, nanosensors, and high-density magnetic memory. Helical magnetic nanosprings are unique objects with remarkable magnetic properties, in...

We experimentally study the structure and dynamics of magnetic domains in synthetic antiferromagnets based on Co/Ru/Co films. Dramatic effects arise from the interaction among the topological defects comprising the dual domain walls in these structures. Under applied magnetic fields, the dual domain walls propagate following the dynamics of bi-mero...

Operating modes of terahertz (THz) generators with “rod–film” magnetic junctions formed by a Fe rod with one pointed end with a diameter of 10–50 nm and various nanometer-thick (single-layer and multilayer) Со films are studied. It is demonstrated that the efficiency of the THz radiation increases (due to an increase in the current density) if the...

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) generally arises in "heavy metal/ferromagnet" (HM/FM) heterostructures due the strong spin-orbit coupling in HM and plays a crucial role in nucleation of Dzyaloshinskii domain walls and skyrmions that can be efficiently moved by spin-orbit torques. Here, we study iDMI in W/CoFeB/MgO/Ta films...

An enhancement of the spin-orbit effects arising on an interface between a ferromagnet (FM) and a heavy metal (HM) is possible through the strong breaking of the structural inversion symmetry in the layered films. Here, we show that an introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular ma...