arXiv subjects

Yuri Dahnovsky

Publications and source records attributed to Yuri Dahnovsky.

5 recordsLinked to original sources

arXiv2026

Skyrmion Phase Control by Magnetic Dipole-Dipole Interaction and Electric Field in Centrosymmetric Materials

Establishing precise control over the helicity and spatial configuration of magnetic skyrmions will be essential to realize their promise in classical, analog and quantum computation applications. In this work, we explore the role of magnetic dipole-dipole interactions, external electric fields, and magnetic fields in controlling these parameters within a triangular lattice centrosymmetric skyrmion host. We demonstrate that dipole-dipole interactions strongly favor Bloch helicity. Notably, a zero magnetic field skyrmion phase appears upon raising the dipole-dipole coupling strength, with substantial potential for cost-effective quantum device applications. We also report the emergence of a meron/antimeron lattice phase, in the absence of any Dzyaloshinskii-Moriya interaction. In contrast, applied electric fields stabilize high density N\'eel skyrmion crystals. The interplay between dipole-dipole interactions and external electric fields creates a continuous transition between the two skyrmion types, rather than an abrupt switch. Applied electric fields can therefore be used as a continuous tuning mechanism for skyrmion helicity, and hence a control handle for tuning two-level systems in skyrmion qubits.

cond-mat.str-el↗

arXiv2024

Tunneling current-controlled spin states in few-layer van der Waals magnets

Effective control of magnetic phases in two-dimensional magnets would constitute crucial progress in spintronics, holding great potential for future computing technologies. Here, we report a new approach of leveraging tunneling current as a tool for controlling spin states in CrI3. We reveal that a tunneling current can deterministically switch between spin-parallel and spin-antiparallel states in few-layer CrI3, depending on the polarity and amplitude of the current. We propose a mechanism involving nonequilibrium spin accumulation in the graphene electrodes in contact with the CrI3 layers. We further demonstrate tunneling current-tunable stochastic switching between multiple spin states of the CrI3 tunnel devices, which goes beyond conventional bi-stable stochastic magnetic tunnel junctions and has not been documented in two-dimensional magnets. Our findings not only address the existing knowledge gap concerning the influence of tunneling currents in controlling the magnetism in two-dimensional magnets, but also unlock possibilities for energy-efficient probabilistic and neuromorphic computing.

cond-mat.mes-hall↗

arXiv2024

Giant and negative magnetoresistances in conical magnets

We study magnetotransport in conical helimagnet crystals. Spin dependent magnetoresistance exhibits dramatic properties for high and low electron concentrations at different temperatures. For spin up electrons we find negative magnetoresistance despite only considering a single carrier type. For spin down electrons we observe giant magnetoresistance due to depletion of spin down electrons with an applied magnetic field. For spin up carriers, the magnetoresistance is negative, due to the increase in charge carriers with a magnetic field. In addition, we investigate spin dependent Hall effect. If a magnetic field reaches some critical value for spin down electrons, giant Hall resistance occurs, i.e., Hall current vanishes. This effect is explained by the absence of spin down carriers. For spin up carriers, the Hall constant dramatically decreases with field, due to the increase in spin up electron density. Because of the giant spin dependent magnetoresistance and Hall resistivity, conical helimagnets could be useful in spin switching devices.

cond-mat.mes-hall↗

arXiv2022

The theory of transport in helical spin-structure crystals

We study helical structures in spin-spiral single crystals. In the continuum approach for the helicity potential energy the simple electronic band splits into two non-parabolic bands. For the Fermi energy greater than the splitting between the bands, the lower band is described by a surface with a saddle shape in the direction of the helicity axis. Using the Boltzmann equation with the relaxation due to acoustic phonons, we discover the dependence of the current on the angle between the electric field and helicity axis leading to the both parallel and perpendicular to the electric field components in the electroconductivity. In addition, we find that the transition rates depend on an electron spin allowing the transition between the bands. The electric conductivities exhibit nonlinear behaviors with respect to chemical potential. We explain this effect as the interference of the band anisotropy, spin conservation, and interband transitions. The proposed theory with the spherical model in the effective mass approximation for conduction electrons can elucidate nonlinear dependencies that can be identified in experiments. There is the excellent agreement between the theoretical and experimental data for parallel resistivity depending on temperature at the phase transition from helical to ferromagnetic state in a MnP single crystal. In addition, we predict that the perpendicular resistivity abruptly drops to zero in the ferromagnetic phase.

cond-mat.mes-hall↗

arXiv2019

Small Energy Gap Revealed in CrBr3 by Scanning Tunneling Spectroscopy

CrBr$_{3}$ is a layered van der Waals material with magnetic ordering down to the 2D limit. For decades, based on optical measurements, it is believed that the energy gap of CrBr$_{3}$ is in the range of 1.68-2.1 eV. However, controversial results have indicated that the band gap of CrBr$_{3}$ is possibly smaller than that. An unambiguous determination of the energy gap is critical to the correct interpretations of the experimental results of CrBr$_{3}$. Here, we present the scanning tunneling microscopy and spectroscopy (STM/S) results of CrBr$_{3}$ thin and thick flakes exfoliated onto pyropytic graphite (HOPG) surfaces and density functional theory (DFT) calculations to reveal the small energy gap (peak-to-peak energy gap to be 0.57 eV $\pm$ 0.04 eV; or the onset signal energy gap to be 0.29 $\pm$ 0.05 eV from dI/dV spectra). Atomic resolution topography images show the defect-free crystal structure and the dI/dV spectra exhibit multiple peak features measured at 77 K. The conduction band - valence band peak pairs in the multi-peak dI/dV spectrum agree very well with all reported optical transitions. STM topography images of mono- and bi-layer CrBr$_{3}$ flakes exhibit edge degradation due to short air exposure (~15 min) during sample transfer. The unambiguously determined small energy gap settles the controversy and is the key in better understanding CrBr$_{3}$ and similar materials.

cond-mat.mtrl-sci↗