arXiv subjects

E. A. Karashtin

Publications and source records attributed to E. A. Karashtin.

8 recordsLinked to original sources

arXiv2026

Transformation of the gyrotropic mode spectrum of the FM / AFM disk via vortex imprinting

We experimentally investigate the magnetic gyrotropic mode in a system of vortex ferromagnetic (FM) nanooscillator exchange coupled to an antiferromagnetic (AFM) layer. The micron-sized disks formed from the $Ni_{80}Fe_{20}$ (12 nm) / $Ir_{80}Mn_{20}$ (5 nm) FM/AFM heterostructure are prepared so that the vortex magnetic state is imprinted into the AFM layer. We apply a magnetic resonance force microscopy (MRFM) method to locally study magnetic oscillations in single FM/AFM disks. We show that the gyrotropic mode frequency is significantly (approximately four times) shifted to the high frequency range compared to a similar structure consisting of a single ferromagnetic disk. Upon applying an in-plane magnetic field, we observe a strong peak at a double frequency which was previously predicted in theory. This shows that nonlinearity in vortex dynamics is strongly enhanced in the FM/AFM system under investigation. Thus the magnetic imprinting technology reveals great potential for future application in high-frequency spintronic devices.

cond-mat.other↗

arXiv2026

Spintronic THz emitters based on NiCu alloys

We study THz emission from ferromagnet / nonmagnetic material (FM/NM) spintronic nanostructures in which the $Ni_xCu_{1-x}$ alloy with different $x$ is used as an FM, an NM, or both layers. The stoichiometric composition of the NiCu alloys standing at two positions (we denote it as [FM] or [PM]) is chosen so that it is ferromagnetic at room temperature in the case it is used as the FM layer, and is paramagnetic at room temperature for the NM layer. Besides, we choose the nickel ratio $x$ close to each other for both [FM] and [PM] types of the alloy (the difference is only $10\%$). We show that although NiCu[PM] does not contain heavy metal it acts as an effective converter of spin current into the electric one in our structure showing only 2.8 times smaller efficiency than Pt. Besides, the NiCu[FM] alloy, despite having quite small Curie temperature (approximately $65 ^\circ C$), acts as an effective spin source having the efficiency only 2 times smaller than Co in similar structures. This shows up the importance of boundary matching in the spintronic THz sources. Our NiCu-based THz sources reveal a possibility of effective thermally induced control of emission of THz radiation due to a unique combination of high emission rate and relatively small Curie temperature.

cond-mat.other↗

arXiv2022

Extrinsic tunnel Hall effect in CoFeB/MgO/Pt junctions

The Hall effect that occurs when current flows through a CoFeB/MgO/Pt tunnel junction is investigated. It is shown that the transverse voltage in Pt electrode is nonlinear on a DC voltage applied to the tunnel junction. It has both linear (odd) and quadratic (even) parts. The linear part contains well-known contributions of the anomalous Hall effect in the ferromagnetic electrode, inverse spin-hall effect in platinum and others. The quadratic part is a phenomenon caused by the spin-orbit scattering of electrons in an external electric field induced by a voltage applied to the barrier. This field reaches values of $10^9$ V/m which is close to internal atomic fields. The magnitude of both effects decreases as thickness of Pt electrode is increased due to shunting effects.

cond-mat.other↗

arXiv2019

Diode effect in the lateral spin valve

We propose a possible experimental setup for nonreciprocal electron transport in a lateral spin valve due to noncoplanar distribution of magnetic moment (and field) in the system. Some metals (Al, Cu) and semiconductors (GaAs, InSb etc.) demonstrate spin accumulation even at room temperatures due to large spin flip lengths (0.3--2.0 $μm$). The Hanle precession was observed in lateral spin valves based on such materials and two parallel magnetic electrodes. We provide theoretical estimations which show that the nonreciprocal effect in a configuration with non-parallel magnetic electrodes is of the same order of value as the effect that arise due to Hanle precession. This makes it possible to observe the nonreciprocal electron transport as a manifestation of the noncommutativity of spin-1/2 algebra for them in the proposed system. Such property of noncoplanar magnetic system has a potential of application in a noncoplanar type of spintronic devices.

cond-mat.mes-hall↗

arXiv2018

Optical second harmonic generation from interfaces between heavy and ferromagnetic metals

Surfaces and interfaces of magnetic nanostructures can reveal rather interesting and unusual properties that differ substantially from those of bulky materials. Here we apply the surface-sensitive method of optical second harmonic generation (SHG) for the studies of magnetization induced effects that appear in the nonlinear reflection from interfaces between ferromagnetic (Co) and heavy metals (Pt, Ta, W, Au, Ag, Cu). We demonstrate the appearance of magnetization induced variation in the p-polarized SHG intensity in the geometry of the longitudinal magneto-optical Kerr effect that is forbidden for homogeneous magnetic structures. This confirms the existence of chiral magnetic states at heavy metal/ferromagnet interfaces that appear due to the surface-induced Dzyaloshinskii-Moriya interaction. The related nonlinear chiroptical effect in the SHG intensity is proportional to the dc flexo-electric polarization that is shown to exist for chiral magnetic states at the considered interfaces.

cond-mat.mes-hall↗

arXiv2017

Spin current and second harmonic generation in non-collinear magnetic systems: the hydrodynamic model

We report a theoretical study of the second harmonic generation in a noncollinearly magnetized conductive medium with equilibrium spin current. The hydrodynamic model is used to unravel the mechanism of a novel effect of the double frequency signal generation due to the spin current. According to our calculations, this second harmonic response appears due to the "non-adiabatic" spin polarization of the conduction electrons induced by the oscillations in the non-uniform magnetization forced by the electric field of the electromagnetic wave. Together with the linear velocity response this leads to the generation of the double frequency spin current. This spin current is converted to the electric current via the inverse Spin Hall effect, and the double-frequency electric current emits the second harmonic radiation.

cond-mat.other↗

arXiv2016

Interlayer interaction in multilayer CoPt/Co structures

We report a study of interlayer exchange interaction in multilayer CoPt/Co structures consisting of periodic CoPt multilayer film with an "easy axis" anisotropy and thick Co layer with an "easy plane" anisotropy separated by Pt spacer with variable thickness. The magnetooptical Kerr effect (MOKE) and ferromagnetic resonance (FMR) measurements show up the essentially non-collinear state of magnetic moments of the layers and strong exchange coupling between CoPt and Co subsystems. The estimation of effective anisotropy and exchange coupling in a simple model based on the Landau-Lifshitz-Gilbert equation describing magnetization dynamics was performed.

cond-mat.mes-hall↗

arXiv2012

Non-reciprocal light scattering by lattice of magnetic vortices

We report on experimental study of optical properties of two-dimensional square lattice of triangle Co and CoFe nanoparticles with a vortex magnetization distribution. We demonstrate that intensity of light scattered in diffraction maxima depends on the vorticity of the particles magnetization and it can be manipulated by applying an external magnetic field. The experimental results can be understood in terms of phenomenological theory.

cond-mat.mes-hall↗