arXiv subjects

Andrei Kirilyuk

Publications and source records attributed to Andrei Kirilyuk.

At least 19 recordsLinked to original sources

arXiv2026

Ferroelastic domain switching by ultrafast photoinduced strain

The crystal lattice underpins the fundamental properties of condensed matter, with ferroic order emerging sensitively from atomic coordination. Manipulating the lattic therefore promises a direct way to switch ferroics between their states. Infrared excitation provides an efficient pathway to drive lattice motion and generate transient crystal deformations and strains. Ferroelastics constitute a uniquely direct platform for such control, their order parameter being strain itself. However, whether ultrafast laser-induced lattice distortions can switch ferroelastic order remains unknown. Here we use ultrafast pump-probe microscopy to demonstrate that a single high-amplitude infrared pulse induces strain within the first nanosecond, followed by ferroelastic domain switching several nanoseconds later. The spatial distribution follows that expected from the photoinduced strain field, while their temporal evolution is closely coupled to the strain dynamics. Our observations identify transient strain as the driving field for ferroelastic switching and suggest a general lattice-mediated pathway for controlling ferroic order using infrared light.

cond-mat.mtrl-sci↗

arXiv2026

Single-pulse strain-induced precessional dynamics of magnetization in Co-doped iron garnet

Ultrafast control of magnetization through lattice excitation provides a route to manipulating magnetic order on short timescales, yet the role of transient strain in driving magnetization dynamics remains poorly understood. Here, single-shot pump-probe magneto-optical microscopy is used to resolve the structural and magnetic responses of cobalt-doped yttrium iron garnet to individual 5-ps mid-infrared pulses. The excitation generates a localized strain field together with an outward-propagating elastic wave. Concurrently, the magnetic contrast decreases following excitation and subsequently reverses on a timescale of approximately 1.5-2 ns before recovering to its initial state. The structural and magnetic responses exhibit closely correlated wavelength and pulse-energy dependences, indicating a common excitation pathway. Micromagnetic simulations incorporating transient strain reproduce the precessional reorientation of the magnetization within individual domains while largely preserving the labyrinthine domain morphology. These results identify transient lattice deformation as the link between single-pulse mid-infrared excitation and reversible precessional magnetization dynamics in Co-doped yttrium iron garnet.

cond-mat.mtrl-sci↗

arXiv2026

Optical switching of antiferromagnetic domains by nonreciprocal heat current

What distinguishes front from back? In physics, such directionality emerges only when an underlying symmetry is broken. Antiferromagnets that inherently break both space-inversion and time-reversal symmetries provide a striking example, exhibiting nonreciprocal optical responses that depend on the direction of light propagation. Beyond distinguishing antiferromagnetic domains, we show that this nonreciprocity can deterministically create them. Using mid-infrared light, we demonstrate deterministic switching of antiferromagnetic domains in the magnetoelectric antiferromagnet LiFePO4, where illumination from opposite sides selectively stabilizes opposite domain states. Remarkably, the switching persists over a broad wavelength range rather than being confined to a narrow transition-specific spectral region, overcoming the spectral and material constraints of resonance-based optical switching schemes. The broadband switching originates from the material's intrinsic nonreciprocity through optically generated heat currents. Our results establish nonreciprocity as a general principle for deterministically controlling symmetry-broken phases with light.

cond-mat.str-el↗

arXiv2026

Photoinduced strain and polarization switching in barium titanate in the far-infrared spectral range

Short mid-infrared laser pulses efficiently facilitate ultrafast manipulation of ferroic order parameters, including full reversal of magnetization or ferroelectric polarization, with the invoked mechanisms relating to the properties of polar phonons in ionic crystals. Much less is known, however, about the behaviour of such order parameters in response to an excitation in the far-infrared range, where phonons are more collective and less polar. Here we investigate transient crystallographic strains and polarization switching in ferroelectric barium titanate (BaTiO3) driven by an excitation in the frequency range of 5-8 THz, or wavelengths of 35-60 um. We find that switching persists in a large part of this range, but is governed primarily by optical absorption rather than by the longitudinal optical phonons or epsilon-near-zero conditions that dominate in the mid-infrared regime.

cond-mat.mtrl-sci↗

arXiv2025

Photo-induced switching of magnetisation in the epsilon-near-zero regime

The possibility of controlling spins using ultrashort light and strain pulses has triggered intense discussions about the mechanisms responsible for magnetic re-ordering. All-optical magnetisation switching can be achieved through ultrafast heat-driven demagnetisation or transient modifications of magnetic anisotropy. During the phononic switching of magnetic dielectrics, however, mid-infrared optical excitations can modify the crystal environment via both the thermal quenching of anisotropy and the generation of strain respectively, with the relative distinction between these thermal and non-thermal processes remaining an open question. Here, we examine the effect of mid-infrared pulses tuned to the frequency of optical phonon resonances on the labyrinthine domain structure of a cobalt-doped yttrium iron garnet film. We find that the labyrinthine domains are transformed into stable parallel stripes, and quantitative micromagnetic calculations demonstrate this stems predominantly from a partial quenching of the anisotropy. Contrary to conventional wisdom, however, we find that this heat-facilitated process of magnetisation switching is spectrally strongest not at the maximum of absorbed optical energy but rather at the epsilon-near-zero points. Our results reveal that the epsilon-near-zero condition provides an alternative pathway for laser-driven control of magnetisation, even when the underlying mechanism is primarily thermal.

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

Disentangling thermal birefringence and strain in the all-optical switching of ferroelectric polarization

Recent works have demonstrated that the optical excitation of crystalline materials with intense narrow-band infrared pulses, tailored to match the frequencies at which the crystal's permittivity approaches close to zero, can drive a permanent reversal of magnetic and ferroelectric ordering. However, the physical mechanism that microscopically underpins this effect remains unclear, as well as the precise role of laser-induced heating and macroscopic strains. Here, we explore how infrared pulses can simultaneously give rise to strong temperature-dependent birefringence and strain in ferroelectric barium titanate. We develop a model of these two coexisting effects, allowing us to use polarization microscopy to disentangle them through their spatial distributions, temporal evolutions and spectral dependencies. We experimentally observe strain-induced patterns that are an order of magnitude larger than that which can be accounted for by laser-induced heating alone, suggesting that non-thermal effects must also play a role. Our results reveal the distinct fingerprints of heat- and strain-induced birefringence, shedding new light on the process of all-optical switching of order parameters in the epsilon-near-zero regime.

cond-mat.mtrl-sci↗

arXiv2023

Epsilon-near-zero regime as the key to ultrafast control of functional properties of solids

Strong light-matter interaction constitutes the bedrock of all photonic applications, empowering material elements with the ability to create and mediate interactions of light with light. Amidst the quest to identify new agents facilitating such efficient light-matter interactions, a class of promising materials have emerged featuring highly unusual properties deriving from their dielectric constant ε being equal, or at least very close, to zero. Works so far have shown that the enhanced nonlinear optical effects displayed in this 'epsilon-near-zero' (ENZ) regime makes it possible to create ultrafast albeit transient optical switches. An outstanding question, however, relates to whether one could use the amplification of light-matter interactions at the ENZ conditions to achieve permanent switching. Here, we demonstrate that an ultrafast excitation under ENZ conditions can induce permanent all-optical reversal of ferroelectric polarization between different stable states. Our reliance on ENZ conditions that naturally emerge from the solid's ionic lattice, rather than specific material properties, suggests that the demonstrated mechanism of reversal is truly universal, being capable of permanently switching order parameters in a wide variety of systems.

cond-mat.mtrl-sci↗

arXiv2022

Dynamic complex opto-magnetic holography

Computer-generated holograms with their animated, three-dimensional appearance have long appealed to our imagination as the path towards truly immersive displays with bi-directional natural parallax. Impressive progress in updateable 3-D imagery has been achieved with liquid crystal modulators and high-resolution, but quasi-static holograms are being recorded in photosensitive materials. However, the memory requirements and computational loads of real-time, large-area holography will be hard to tackle for several decades to come with the current paradigm based on a matrix calculations and bit-plane writing. Here, we experimentally demonstrate a conceptually novel, holistic approach to serial computation and repeatable writing of computer-generated dynamic holograms without Fourier transform, using minimal amounts of computer memory. We use the ultrafast opto-magnetic recording of holographic patterns in a ferrimagnetic film with femtosecond laser pulses, driven by on-the-fly hardware computation of a single holographic point. The intensity-threshold nature of the magnetic medium allows sub-diffraction-limited, point-by-point toggling of arbitrarily localized magnetic spots on the sample, according to the proposed circular detour-phase encoding, providing complex modulation and symmetrical suppression of upper diffractive orders and conjugated terms in holographically reconstructed 3-D images.

physics.optics↗

arXiv2022

Strongly nonlinear antiferromagnetic dynamics in high magnetic fields

Antiferromagnetic (AFM) materials possess a well-recognized potential for ultrafast data processing thanks to their intrinsic ultrafast spin dynamics, absence of stray fields, and large spin transport effects. The very same properties, however, make their manipulation difficult, requiring frequencies in THz range and magnetic fields of tens of Teslas. Switching of AFM order implies going into the nonlinear regime, a largely unexplored territory. Here we use THz light from a free electron laser to drive antiferromagnetic NiO into a highly nonlinear regime and steer it out of nonlinearity with magnetic field from a 33-Tesla Bitter magnet. This demonstration of large-amplitude dynamics represents a crucial step towards ultrafast resonant switching of AFM order.

cond-mat.mtrl-sci↗

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↗

arXiv2021

Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling

The quest to improve density, speed and energy efficiency of magnetic memory storage has led to exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy-funneling plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film. We demonstrate how Ag nanoring-shaped antennas under resonant optical femtosecond pumping reduce the overall magneto-optical response due to demagnetization in the underlying films up to three times compared to non-resonant illumination. We attribute such substantial reduction to the nanoscale confinement of the demagnetization process. This is qualitatively supported by the electromagnetic simulations that strongly evidence the optical energy-funneling to the nanoscale from the nanoantennas into the ferrimagnetic film. This is the first and defining step for reaching deterministic ultrafast all-optical magnetization switching at the nanoscale in such systems, opening a route to develop nanoscale ultrafast magneto-optics.

physics.optics↗

arXiv2021

All-optical spin switching probability in [Tb/Co] multilayers

Since the first experimental observation of all-optical switching phenomena, intensive research has been focused on finding suitable magnetic systems that can be integrated as storage elements within spintronic devices and whose magnetization can be controlled through ultra-short single laser pulses. We report here atomistic spin simulations of all-optical switching in multilayered structures alternating n monolayers of Tb and m monolayers of Co. By using a two temperature model, we numerically calculate the thermal variation of the magnetization of each sublattice as well as the magnetization dynamics of [Tbn/Com] multilayers upon incidence of a single laser pulse. In particular, the condition to observe thermally-induced magnetization switching is investigated upon varying systematically both the composition of the sample (n,m) and the laser fluence. The samples with one monolayer of Tb as [Tb1/Co2] and [Tb1/Co3] are showing thermally induced magnetization switching above a fluence threshold. The reversal mechanism is mediated by the residual magnetization of the Tb lattice while the Co is fully demagnetized in agreement with the models developed for ferrimagnetic alloys. The switching is however not fully deterministic but the error rate can be tuned by the damping parameter. Increasing the number of monolayers the switching becomes completely stochastic. The intermixing at the Tb/Co interfaces appears to be a promising way to reduce the stochasticity. These results predict for the first time the possibility of TIMS in [Tb/Co] multilayers and suggest the occurrence of sub-picosecond magnetization reversal using single laser pulses.

physics.app-ph↗

arXiv2020

Magnetic and all-optical switching properties of amorphous Tb$_x$Co$_{100-x}$ alloys

Amorphous Tb$_{x}$Co$_{100-x}$ magnetic alloys exhibit a list of intriguing properties, such as perpendicular magnetic anisotropy, high magneto-optical activity and magnetization switching using ultrashort optical pulses. Varying the Tb:Co ratio in these alloys allows for tuning properties such as the saturation magnetic moment, coercive field and the performance of the light-induced magnetization switching. In this work, we investigate the magnetic, optical and magneto-optical properties of various Tb$_{x}$Co$_{100-x}$ thin film alloy compositions. We report on the effect the choice of different seeding layers has on the structural and magnetic properties of Tb$_{x}$Co$_{100-x}$ layers. We also demonstrate that for a range of alloys, deposited on fused silica substrates, with Tb content of 24-30 at.$\%$, helicity dependent all-optical switching of magnetization can be achieved, albeit in a multi-shot framework. We explain this property to arise from the helicity-dependent laser induced magnetization on the Co sublattice due to the inverse Faraday effect. Our study provides an insight into material aspects for future potential hybrid magneto-plasmonic TbCo-based architectures.

physics.app-ph↗

arXiv2018

Frequency and wavenumber selective excitation of spin waves through coherent energy transfer from elastic waves

Using spin-wave tomography (SWaT), we have investigated the excitation and the propagation dynamics of optically-excited magnetoelastic waves, i.e. hybridized modes of spin waves and elastic waves, in a garnet film. By using time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves through coherent-energy transfer between optically-excited pure-elastic waves and spin waves via magnetoelastic coupling. This process realizes frequency and wavenumber selective excitation of spin waves at the crossing of the dispersion relations of spin waves and elastic waves. Finally, we demonstrate that the excitation mechanism of the optically-excited pure-elastic waves, which are the source of the observed magnetoelastic waves, is dissipative in nature.

cond-mat.mtrl-sci↗

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↗

arXiv2016

Magnetism and exchange interaction of small rare-earth clusters; Tb as a representative

Here we follow, both experimentally and theoretically, the development of magnetism in Tb clusters from the atomic limit, adding one atom at a time. The exchange interaction is, surprisingly, observed to drastically increase compared to that of bulk, and to exhibit irregular oscillations as a function of the interatomic distance. From electronic structure theory we find that the theoretical magnetic moments oscillate with cluster size in exact agreement with experimental data. Unlike the bulk, the oscillation is not caused by the RKKY mechanism. Instead, the inter-atomic exchange is shown to be driven by a competition between wave-function overlap of the 5d shell and the on-site exchange interaction, which leads to a competition between ferromagnetic double-exchange and antiferromagnetic super-exchange. This understanding opens up new ways to tune the magnetic properties of rare-earth based magnets with nano-sized building blocks.

physics.atm-clus↗

arXiv2015

All-thermal switching of amorphous Gd-Fe alloys: analysis of structural properties and magnetization dynamics

In recent years, there has been an intense interest in understanding the microscopic mechanism of thermally induced magnetization switching driven by a femtosecond laser pulse. Most of the effort has been dedicated to periodic crystalline structures while the amorphous counterparts have been less studied. By using a multiscale approach, i.e. first-principles density functional theory combined with atomistic spin dynamics, we report here on the very intricate structural and magnetic nature of amorphous Gd-Fe alloys for a wide range of Gd and Fe atomic concentrations at the nanoscale level. Both structural and dynamical properties of Gd-Fe alloys reported in this work are in good agreement with previous experiments. We calculated the dynamic behavior of homogeneous and inhomogeneous amorphous Gd-Fe alloys and their response under the influence of a femtosecond laser pulse. In the homogeneous sample, the Fe sublattice switches its magnetization before the Gd one. However, the temporal sequence of the switching of the two sublattices is reversed in the inhomogeneous sample. We propose a possible explanation based on a mechanism driven by a combination of the Dzyaloshiskii-Moriya interaction and exchange frustration, modeled by an antiferromagnetic second-neighbour exchange interaction between Gd atoms in the Gd-rich region. We also report on the influence of laser fluence and damping effects in the all-thermal switching.

cond-mat.mtrl-sci↗