arXiv subjects

Alexey V. Kimel

Publications and source records attributed to Alexey V. Kimel.

12 recordsLinked to original sources

arXiv2026

Double-pulse control of all optical magnetization reversal in Tb/Co multilayers

Recent experiments have shown that femtosecond laser pulse with a Gaussian intensity profile can induce magnetization reversal in Tb/Co multilayers with a ring-shaped switching pattern within the laser-irradiated area. Here, we investigate the ultrafast magnetization dynamics leading to such a ring-shaped switching by using double-pulse laser excitation. The laser pulses cause heat-induced quenching and subsequent recovery of the magnetic anisotropy in the multilayers and drive the precessional magnetization switching in the magnetic multilayers. By adjusting the delay between the two pump pulses, we demonstrate that the recovery process can be manipulated and show, experimentally and numerically, that this allows control over the final magnetic domain pattern.

cond-mat.mtrl-sci↗

arXiv2026

Engineering photomagnetism in collinear van der Waals antiferromagnets

Achieving efficient ultrafast optical control of antiferromagnetic spin dynamics is a central goal for next-generation high-speed THz spintronic and magnonic devices. Resonant optical pumping of crystal-field-split d-d orbital multiplets in magnetic TM ions directly modulates exchange and spin-orbit interactions, inducing large-amplitude coherent spin precession. However, such effects are limited to a handful of systems and there is no general strategy to enhance d-d photomagnetism in antiferromagnets. Here, we demonstrate the engineering of photomagnetism via TM-ion doping in collinear van der Waals antiferromagnets. In Mn$_{1-x}$Ni$_x$PS$_3$, small amounts of Ni$^{2+}$ activate a strong photomagnetic response while largely preserving the Néel ground state. Even 10% Ni boosts the response by more than an order of magnitude compared to pure MnPS$_3$, with resonant pumping of Ni$^{2+}$ d-d transitions driving large-amplitude coherent spin precession and providing helicity-dependent phase control. Tuning the pump energy across the full Mn$_{1-x}$Ni$_x$PS$_3$ composition range shows that Ni excitations remain effective across competing Néel and zig-zag antiferromagnetic states while supporting tunable-frequency coherent spin precession. These results establish TM-ion doping as a versatile strategy to harness orbital multiplet excitations for ultrafast, low-dissipation spin control in van der Waals antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2025

X-ray View of Light-Induced Spin Reorientation in TmFeO$_{3}$: Direct Observation of a 90$^\circ$ Néel Vector Rotation

Using time-resolved X-ray magnetic linear dichroism in reflection, we provide a direct probe of the Néel vector dynamics in TmFeO$_3$ on a ultrafast timescale. Our measurements reveal that, following optical excitation, the Néel vector undergoes a spin reorientation transition primarily within the a-c plane, completing a full 90° rotation within approximately 20 ps. This study highlights the ability to probe dynamics of antiferromagnets at its intrinsic timescale in reflection geometry, paving the way for investigations of a wide range of antiferromagnets grown on application relevant substrates.

cond-mat.mtrl-sci↗

arXiv2024

Magnetization reversal of a ferromagnetic Pt/Co/Pt film by helicity dependent absorption of visible to near-infrared laser pulses

The practical difficulty in distinguishing the impact of magnetic circular dichroism and the inverse Faraday effect fuels intense debates over which mechanism predominantly drives the process of helicity dependent all-optical switching of magnetization in ferromagnets. Here, we quantitatively measure the efficiency of the switching process in a Pt/Co/Pt multilayered stack using visible- to near-infrared optical pulses. We find that the switching efficiency increases by a factor of 8.6 upon increasing the pumping wavelength from 0.5 $ μ$m to 1.1 $ μ$m, becoming 100 % efficient at even longer wavelengths up to 2.0 $ μ$m. Our experimental results can be successfully explained by the phenomenon of magnetic circular dichroism, making a significant step towards resolving the long-standing controversy over the origin of the all-optical process of magnetization reversal in ferromagnets.

cond-mat.mtrl-sci↗

arXiv2024

Separating terahertz spin and charge contributions from ultrathin antiferromagnetic heterostructures

Femtosecond laser excitation of nanometer thin heterostructures comprising a heavy metal and a magnetically ordered material is known to result in the emission of terahertz radiation. However, the nature of the emitted radiation from heavy metal~/~antiferromagnet heterostructures has sparked debates and controversies in the literature. Here, we unambiguously separate spin and charge contributions from Pt~/~NiO heterostructures by introducing an unprecedented methodology combining high external magnetic fields with a symmetry analysis of the emitted terahertz polarization. We observe two distinct mechanisms of terahertz emission which we identify as optical difference frequency generation and ultrafast laser-induced quenching of the magnetization. We emphasize the absence of spin transport effects and signatures of coherent magnons. Overall, our work provides a general experimental methodology to separate spin and charge contributions to the laser-induced terahertz emission from heterostructures comprising a magnetically ordered material thus holding great potential for advancing terahertz spintronics and establishing terahertz orbitronics.

cond-mat.mes-hall↗

arXiv2023

Impulsive Fermi magnon-phonon resonance in antiferromagnetic $CoF_{2}$

Understanding spin-lattice interactions in antiferromagnets is one of the most fundamental issues at the core of the recently emerging and booming fields of antiferromagnetic spintronics and magnonics. Recently, coherent nonlinear spin-lattice coupling was discovered in an antiferromagnet which opened the possibility to control the nonlinear coupling strength and thus showing a novel pathway to coherently control magnon-phonon dynamics. Here, utilizing intense narrow band terahertz (THz) pulses and tunable magnetic fields up to 7 T, we experimentally realize the conditions of the Fermi magnon-phonon resonance in antiferromagnetic $CoF_{2}$. These conditions imply that both the spin and the lattice anharmonicities harvest energy transfer between the subsystems, if the magnon eigenfrequency $f_{m}$ is twice lower than the frequency of the phonon $2f_{m}=f_{ph}$. Performing THz pump-infrared probe spectroscopy in conjunction with simulations, we explore the coupled magnon-phonon dynamics in the vicinity of the Fermi-resonance and reveal the corresponding fingerprints of an impulsive THz-induced response. This study focuses on the role of nonlinearity in spin-lattice interactions, providing insights into the control of coherent magnon-phonon energy exchange.

cond-mat.mes-hall↗

arXiv2021

Terahertz-Light Driven Coupling of Antiferromagnetic Spins to Lattice

Understanding spin-lattice coupling represents a key challenge in modern condensed matter physics, with crucial importance and implications for ultrafast and 2D-magnetism. The efficiency of angular momentum and energy transfer between spins and the lattice imposes fundamental speed limits on the ability to control spins in spintronics, magnonics and magnetic data storage. We report on an efficient nonlinear mechanism of spin-lattice coupling driven by THz light pulses. A nearly single-cycle THz pulse resonantly interacts with a coherent magnonic state in the antiferromagnet CoF2 and excites the Raman-active THz phonon. The results reveal the unique functionality of antiferromagnets allowing ultrafast spin-lattice coupling using light.

cond-mat.str-el↗

arXiv2021

Efficient all-optical helicity dependent switching of spins in a Pt/Co/Pt film by a dual-pulse excitation

All-optical helicity dependent switching (AO-HDS), deterministic control of magnetization by circularly polarized laser pulses, allows to efficiently manipulate spins without the need of a magnetic field. However, AO-HDS in ferromagnetic metals so far requires many laser pulses for fully switching their magnetic states. Using a combination of a short, 90-fs linearly polarized pulse and a subsequent longer, 3-ps circularly polarized pulse, we demonstrate that the number of pulses for full magnetization reversal can be reduced to 4 pulse pairs in a single stack of Pt/Co/Pt. The obtained results suggest that the dual-pulse approach is a potential route towards realizing efficient AO-HDS in ferromagnetic metals.

cond-mat.mtrl-sci↗

arXiv2020

Femtosecond Photocurrents at the Pt/FeRh Interface

Femtosecond laser excitation of FeRh/Pt bilayers launches an ultrafast pulse of electric photocurrent in the Pt-layer and thus results in emission of electromagnetic radiation in the THz spectral range. Analysis of the THz emission as a function of polarization of the femtosecond laser pulse, external magnetic field, sample temperature and sample orientation shows that photocurrent can emerge due to vertical spin pumping and photo-induced inverse spin-orbit torque at the FeRh/Pt interface. The vertical spin pumping from FeRh to Pt does not depend on the polarization of light and originates from ultrafast laser-induced demagnetization of the ferromagnetic phase of FeRh. The photo-induced inverse spin-orbit torque at the FeRh/Pt interface can be described in terms of a helicity-dependent effect of circularly polarized light on the magnetization of the ferromagnetic FeRh and subsequent generation of a photocurrent.

cond-mat.mes-hall↗

arXiv2016

Mechanism of all-optical control of ferromagnetic multilayers with circularly polarized light

Time-resolved imaging reveals that the helicity dependent all-optical switching (HD-AOS) of Co/Pt ferromagnetic multilayers proceeds by two stages. First one involves the helicity independent and stochastic nucleation of reversed magnetic domains. At the second stage circularly polarized light breaks the degeneracy between the magnetic domains and promotes the preferred direction of domain wall (DW) motion. The growth of the reversed domain from the nucleation cite, for a particular helicity, leads to full magnetic reversal. This study demonstrates a novel mechanism of HD-AOS mediated by the deterministic displacement of DWs.

cond-mat.mtrl-sci↗

arXiv2014

Nanoscale confinement of all-optical switching in TbFeCo using plasmonic antennas

All-optical switching (AOS) of magnetic domains by femtosecond laser pulses was first observed in the transition metal-rare earth (TM-RE) alloy GdFeCo1-5; this phenomenon demonstrated the potential for optical control of magnetism for the development of ever faster future magnetic recording technologies. The technological potential of AOS has recently increased due to the discovery of the same effect in other materials, including RE-free magnetic multilayers6,7. However, to be technologically meaningful, AOS must compete with the bit densities of conventional storage devices, restricting optically-switched magnetic areas to sizes well below the diffraction limit. Here, we demonstrate reproducible and robust all-optical switching of magnetic domains of 53 nm size in a ferrimagnetic TbFeCo alloy using gold plasmonic antenna structures. The confined nanoscale magnetic reversal is imaged around and beneath plasmonic antennas using x-ray resonant holographic imaging. Our results demonstrate the potential of future AOS-based magnetic recording technologies.

cond-mat.mes-hall↗

arXiv2012

Optical energy optimization at the nanoscale by near-field interference

Employing plasmonic antennas for subdiffraction focusing of light on recording media requires to take into account the complete structure of the medium, including dielectric cover layers. We find, with finite difference time domain simulations, that optical energy transfer to the magnetic recording layer is most efficient for an off-resonant antenna. Furthermore, we show that the focal spot in the magnetic film is well below the diffraction limit, making nanoscale all-optical magnetic data recording achievable.

physics.optics↗