Alexandra M Kalashnikova

Ioffe Institute | ioffe

Exchange interactions determine the correlations between microscopic spins in magnetic materials. Probing the dynamics of these spin correlations on ultrashort length and time scales is, however, rather challenging, since it requires simultaneously high spatial and high temporal resolution. Recent experimental demonstrations of laser-driven two-mag...

Nonreciprocity, i.e. inequivalence in amplitudes and frequencies of spin waves propagating in opposite directions, is a key property underlying functionality in prospective magnonic devices. Here we demonstrate experimentally and theoretically a simple approach to induce frequency nonreciprocity in a magnetostatically coupled ferromagnetic bilayer...

Low-energy magnonic logic circuits are an actively developing field of modern magnetism. The potential benefits of magnonics for data processing are vitally dependent on units based on nonreciprocal propagation of spin waves, in analogy to semiconductor diodes and transistors in electronics. In this paper, we suggest the approach to realize nonreci...

Ultrafast photo-induced phase transitions occurring under the impact of femtosecond laser pulses provide versatile opportunities for switching solids between distinctly-different crystalline, electronic, and magnetic states and thus modify their functional properties in a significant way. In this paper, we report on the laser-induced spin reorienta...

Exchange interactions determine the correlations between microscopic spins in magnetic materials. Probing the dynamics of these spin correlations on ultrashort length and time scales is, however rather challenging, since it requires simultaneously high spatial and high temporal resolution. Recent experimental demonstrations of laser-driven two-magn...

Coherent THz optical lattice and hybridized phonon‐magnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS3. We investigate the laser‐driven lattice and spin dynamics in a bulk crystal as well as in a 380 nm‐thick exfoliated flake as a function of the excitation photon energy, sample temperat...

Magnetization dynamics of bismuth-substituted yttrium iron-gallium garnet film (Y3−zBiz)[Fe2−xGax][Fe3−yGay]O12 has been studied using a terahertz pump–optical probe spectroscopy. Two magnetic modes are observed whose frequencies intersect at a magnetization compensation point. The experimental dependence of the excited modes on terahertz pulse pol...

Ultrafast photo-induced phase transitions occurring under the impact of femtosecond laser pulses provide versatile opportunities to switch solids between distinctly-different crystalline, electronic, and spin states and thus modify their functional properties in a significant manner. In this paper, we report on the laser-induced spin reorientation...

Nonreciprocity, i.e. inequivalence in amplitudes and frequencies of spin waves propagating in opposite directions, is a key property underlying functionality in prospective magnonic devices. Here we demonstrate experimentally and theoretically a simple approach to induce frequency nonreciprocity in a magnetostatically coupled ferromagnetic bilayer...

Low-energy magnonic logic circuits are an actively developing field of modern magnetism. The potential benefits of magnonics for data processing are vitally dependent on units based on non-reciprocal propagation of spin waves in analogy to semiconductor diodes and transistors in electronics. In this article, we suggest the approach to realize non-r...

The piezomagnetic effect manifests itself in emergence of a net magnetic moment in a mechanically-stressed magnetically ordered material. Up to now, this effect was theoretically analyzed and experimentally studied for the case of static or low frequency deformations of antiferromagnets, and in our brief overview we present the recent progress in e...

In this work, we tackle the problem of the spatially selective optical excitation of spin dynamics in structures with multiple magnetic layers. The 120 fs circularly polarized laser pulses were used to launch magnetization precession in an all-dielectric magneto-photonic crystals (MPC) formed by magnetic layers sandwiched between and inside two mag...

Magnetic tunnel junction (MTJ) is a leading contender for next generation high-density nonvolatile memory technology. Fast and efficient switching of MTJs between different resistance states is a challenging problem, which can be tackled by using an unconventional stimulus-a femtosecond laser pulse. Herein, we report an experimental study of the la...

Magneto-optics was established almost two centuries ago by M. Faraday, who discovered the influence of magnetic field on light polarization [Diary, 1845]. We would like to present this special issue dedicated to the state-of-art in magnetophotonic materials and their applications.

We present an experimental study of ultrafast optical excitation of magnetostatic surface spin wave (MSSW) packets and their spectral properties in thin films of pure iron. As the packets leave the excitation area and propagate in space, their spectra evolve non-trivially. Particularly, low or high frequency components are suppressed at the border...

Excitation, detection, and control of coherent THz magnetic excitation in antiferromagnets are challenging problems that can be addressed using ever shorter laser pulses. We study experimentally excitation of magnetic dynamics at THz frequencies in an antiferromagnetic insulator CoF 2 by sub-10 fs laser pulses. Time-resolved pump-probe polarimetric...

Employing short laser pulses with a duration below 100 fs for changing magnetic state of magnetically-ordered media has developed into a distinct branch of magnetism femtomagnetism which aims at controlling magnetization at ultimately short timescales. Among plethora of femtomagnetic phenomena, there is a class related to impact of femtosecond puls...

A coherent THz optical lattice mode is triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS$_3$. The 380 nm thick exfoliated flake was placed on a substrate and laser-driven lattice and spin dynamics were investigated as a function of the excitation photon energy and sample temperature. The pump-probe spec...

We present the experimental study of ultrafast optical excitation of surface magnetostatic spin wave (MSSW) packets and their spectral properties in thin films of pure iron. As the packets leave the excitation area and propagate in space, their spectra evolve non-trivially. Particularly, low or high frequency components are suppressed at the border...

The rate and pathways of relaxation of a magnetic medium to its equilibrium following excitation with intense and short laser pulses are the key ingredients of ultrafast optical control of spins. Here we study experimentally the evolution of the magnetization and magnetic anisotropy of thin films of a ferromagnetic metal galfenol (Fe0.81Ga0.19) res...

The rate and pathways of relaxation of a magnetic medium to its equilibrium following excitation with intense and short laser pulses are the key ingredients of ultrafast optical control of spins. Here we study experimentally the evolution of the magnetization and magnetic anisotropy of thin films of a ferromagnetic metal galfenol (Fe$_{0.81}$Ga$_{0...

We present a concept of a tunable optical excitation of spin waves and filtering their spectra in a ferromagnetic film with 180° Néel domain wall. We show by means of micromagnetic simulation that the fluence of the femtosecond laser pulse and its position with respect to the domain wall affect the frequencies of the excited spin waves, and the pre...

We present a concept of a tunable optical excitation of spin waves and filtering their spectra in a ferromagnetic film with 180∘ Néel domain wall. We show by means of micromagnetic simulation that the fluence and position of the femtosecond laser pulse affect the frequencies of the excited spin waves, and the presence of the domain wall plays cruci...

Excitation, detection and control of coherent THz magnetic excitation in antiferromagnets are challenging problems which can be addressed using ever shorter laser pulses. We study experimentally excitation of magnetic dynamics at THz frequencies in an antiferromagnetic insulator CoF$_2$ by sub-10 fs laser pulses. Time-resolved pump-probe polarimetr...

We use a picosecond ultrasonic technique to evaluate the photoelastic parameters at the wavelength of 1028 nm in epitaxial vanadium dioxide (VO2) nanolayers grown on c-cut sapphire substrates. In the experiments, we monitor the picosecond evolution of the reflectivity of VO2 in insulating and metallic phases under the impact of a picosecond longitu...

We study experimentally the influence of the laser-induced temperature gradient on the parameters of propagating magnetostatic surface waves in thin film of the ferromagnetic metallic alloy Galfenol Fe 0.81 Ga 0.19 . The material has a pronounced magnetocrystalline anisotropy and exhibits the long-distance propagation of magnetostatic surface waves...

Using a magneto-optical pump-probe technique with micrometer spatial resolution, we show that magnetization precession can be launched in individual magnetic domains imprinted in a Co40Fe40B20 layer by elastic coupling to ferroelectric domains in a BaTiO3 substrate. The dependence of the precession parameters on the strength and orientation of the...

Using a magneto-optical pump-probe technique with micrometer spatial resolution we show that magnetization precession can be launched in individual magnetic domains imprinted in a $\mathrm{Co_{40}Fe_{40}B_{20}}$ (CoFeB) layer by elastic coupling to ferroelectric domains in a BaTiO$_{3}$ substrate. The dependence of the precession parameters on exte...

Picosecond strain pulses are a versatile tool for investigation of mechanical properties of meso- and nano-scale objects with high temporal and spatial resolutions. Generation of such pulses is traditionally realized via ultrafast laser excitation of a light-to-strain transducer involving thermoelastic, deformation potential, or inverse piezoelectr...

We report on experimental picosecond acoustic studies of an ultrafast photoinduced insulator-to-metal and structural transition in VO 2 nanostructures epitaxially grown on Al 2 O 3 substrates with different orientations. Applying a pump-probe technique with combined excitation of a sample with picosecond strain and femtosecond laser pulses we demon...

In this work, CeF3 crystal with maximum diameter of 35 mm was successfully grown with the Bridgman-Stockbarger (BS) method. The crystal diffraction peaks match well with the standard pattern of CeF3 (PDF#01-089-0967), which proofs that obtained samples are of high purity. The transmittance of CeF3 crystal is relatively high in the UV-NIR region and...

The ability to switch ferroics (ferro-, ferri-, antiferromagnets, ferroelectrics, multiferroics) between two stable bit states is one of the keystones of modern data storage technology. Due to many new ideas, originating from fundamental research during the last 50 years, this technology has developed in a breath-taking fashion. Finding a conceptua...

We suggest a model of synthetic ferrimagnetic semiconductor structure based on GaAs-AlGaAs quantum well doped by two Mn delta-layers. The coupling between the delta-layers is mediated by extra holes, and can be switched between ferro- and antiferromagnetic one by gating the structure. A proper choice of Mn concentrations in the delta-layers and of...

Using time-resolved magneto-optical pump-probe technique we demonstrate excitation of magnetization precession in a single crystalline bulk magnetite Fe 3 O 4 below and in the vicinity of the Verwey and spin-reorientation (SR) phase transitions. Pronounced temperature dependence of the precession amplitude is observed suggesting that the excitation...

Using a time-resolved optically pumped scanning-optical-microscopy technique, we demonstrate the laser-driven excitation and propagation of spin waves in a 20-nm film of a ferromagnetic metallic alloy Galfenol epitaxially grown on a GaAs substrate. In contrast to previous all-optical studies of spin waves, we employ laser-induced thermal changes of...

We suggest a model of synthetic ferrimagnetic semiconductor structure based on GaAs-AlGaAs quantum well doped by two Mn delta-layers. The coupling between the delta-layers is mediated by extra holes, and can be switched between ferro- and antiferromagnetic one by gating the structure. A proper choice of Mn concentrations in the delta-layers and of...

Using a time-resolved optically-pumped scanning optical microscopy technique we demonstrate the laser-driven excitation and propagation of spin waves in a 20-nm film of a ferromagnetic metallic alloy Galfenol epitaxially grown on a GaAs substrate. In contrast to previous all-optical studies of spin waves we employ laser-induced thermal changes of m...

Strain engineering is a powerful technology that exploits the stationary external or internal stress of specific spatial distribution for controlling the fundamental properties of condensed materials and nanostructures. This advanced technique modulates in space the carrier density and mobility, the optical absorption, and in strongly correlated sy...

Demands for miniaturization, increasing the operation speed and energy efficiency of electronic devices led to the emergence and rapid development of spin electronics, or spintronics. Several areas of experimental and theoretical research are considered, in which the Ioffe Institute is actively involved. We discuss current progress in developing se...

Strain engineering is a powerful technology which exploits stationary external or internal stress of specific spatial distribution for controllingthe fundamental properties ofcondensed materials and nanostructures. This advanced technique modulates in space the carrier density and mobility, the optical absorption and, in strongly correlated systems...

The excitation of four coherent phonon modes of different symmetries are realized in copper metaborate CuB$_2$O$_4$ via impulsive stimulated Raman scattering (ISRS). The phonons are detected by monitoring changes in the linear optical birefringence using the polarimetric detection (PD) technique. We compare the results of the ISRS-PD experiment to...

We demonstrate spin pumping, i.e. the generation of a pure spin current by precessing magnetization, without application of microwave radiation commonly used in spin pumping experiments. We use femtosecond laser pulses to simultaneously launch the magnetization precession in each of two ferromagnetic layers of a Galfenol-based spin valve and monito...

To gain control over magnetic order on ultrafast time scales, a fundamental understanding of the way electron spins interact with the surrounding crystal lattice is required. However, measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. Here, we directly probe the flow of energy an...

In this paper, multiple magnetic transitions of Sm0.5Pr0.5FeO3 single crystal were systematically studied. By substituting Pr³⁺ in SmFeO3, spin reorientation temperature (TSR) was effectively decreased from 450 K–480 K (SmFeO3) to 180 K–220 K (Sm0.5Pr0.5FeO3). When the applied magnetic field is 500 Oe, spin switching was observed at 119 K (Tssw) fo...

We demonstrate spin pumping, i.e. the generation of a pure spin current by precessing magnetization, without application of microwave radiation commonly used in spin pumping experiments. We use femtosecond laser pulses to simultaneously launch the magnetization precession in each of two ferromagnetic layers of a Galfenol-based spin valve and monito...

We report the high resolution resonant inelastic EUV scattering study of quantum Heisenberg antiferromagnet KCoF3. By tuning the EUV photon energy to cobalt M23 edge, a complete set of low energy 3d spin-orbital excitations is revealed. These low-lying electronic excitations are modeled using an extended multiplet-based mean field calculation to id...

In spintronic materials, control and transport of magnetic order require a fundamental understanding of the way spins interact with the surrounding crystal lattice. However, direct measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. Here, we reveal the flow of energy and angular m...

Dynamical strain generated upon excitation of a metallic film by a femtosecond laser pulse may become a versatile tool enabling control of magnetic state of thin _lms and nanostructures via inverse magnetostriction on a picosecond time scale. Here we explore two alternative approaches to manipulate magnetocrystalline anisotropy and excite magnetiza...

Light propagation effects can strongly influence the excitation and the detection of laser-induced magnetization dynamics. We investigated experimentally and analytically the effects of crystallographic linear birefringence on the excitation and detection of ultrafast magnetization dynamics in the rare-earth orthoferrites (Sm0.5Pr0.5)FeO3 and (Sm0....

In the past few years, we have been witnessing an increased interest for studying materials properties under non-equilibrium conditions. Several well established spectroscopies for experiments in the energy domain have been successfully adapted to the time domain with sub-picosecond time resolution. Here we show the realization of high resolution r...

Dynamical strain generated upon excitation of a metallic film by a femtosecond laser pulse may become a versatile tool enabling control of magnetic state of thin films and nanostructures via inverse magnetostriction on a picosecond time scale. Here we explore two alternative approaches to manipulate magnetocrystalline anisotropy and excite magnetiz...

In this work, Sm0.3Tb0.7FeO3 single crystal was successfully grown by optical floating zone method. Sm0.3Tb0.7FeO3 samples with a-, b-, and c-orientation were manufactured by means of Laue photograph. Magnetic properties of Sm0.3Tb0.7FeO3 single crystals are studied over a wide temperature range from 2 to 400 K. Spin reorientation transition from Γ...

Optical second harmonic generation at the photon energy of 2ℏω = 2eV in the model centrosymmetric antiferromagnet NiO irradiated with picosecond terahertz pulses (0.4–2.5 THz) at room temperature is detected. The analysis of experimental results shows that induced optical second harmonic generation at the moment of the impact of a terahertz pulse a...

Spin-lattice coupling is one of the most prominent interactions mediating response of spin ensemble to ultrafast optical excitation. Here we exploit optically generated coherent and incoherent phonons to drive coherent spin dynamics, i.e. precession, in thin films of magnetostrictive metal Galfenol. We demonstrate unambiguously that coherent phonon...

Spin-lattice coupling is one of the most prominent interactions mediating response of spin ensemble to ultrafast optical excitation. Here we exploit optically generated coherent and incoherent phonons to drive coherent spin dynamics, i.e. precession, in thin films of magnetostrictive metal Galfenol. We demonstrate unambiguously that coherent phonon...

Ultrafast optical excitation of a metal ferromagnetic film results in a modification of the magnetocrystalline anisotropy and induces the magnetization precession. We consider two main contributions to these processes: an effect of noncoherent phonons, which modifies the temperature dependent parameters of the magnetocrystalline anisotropy and cohe...

Experimentally observed ultrafast all-optical magnetization reversal in ferrimagnetic metals and heterostructures based on antiferromagnetically coupled ferromagnetic d- and f-metallic layers relies on intricate energy and angular momentum flow between electrons, phonons, and spins. Here we treat the problem of angular momentum transfer in the cour...

In the last decade, a new area of research, referred to as femtomagnetism, has developed within the field of magnetism, which studies the excitation and control of magnetic medium dynamics on time scales comparable to or even much shorter than those of spin-lattice, spin-orbit, and exchange interactions. Among the many femtomagnetic processes studi...

The goal of this work is to define conditions for the most efficient ultrafast optical control of magnetism. Results show that tuning the composition of the GdFeCo alloys towards the magnetization compensation point as well as reducing the sizes of structures allowing one to reduce the energy of the laser pulse required for ultrafast demagnetizatio...

Ultrafast laser-induced control of the magnetic state of media is the one of the most intriguing and controversial fields of the contemporal condensed matter physics. Changing magnetic anisotropy by a femtosecond laser pulse is one of the most versatile approaches for controlling the magnetic state on the subnanosecond time scale. In this paper we...

We develop a microscopic model allowing to explain ultrafast magnetization reversal by a femtosecond laser pulse, which was recently observed in various structures based on antiferromagnetically coupled metallic ferromagnetic subsystems formed by $d$ and $f$ metals. We show that the reversal is supported by a coupling of these subsystems to delocal...

High quality Sm0.7Tb0.3FeO3 single crystal has been grown by the four-mirror floating zone technique. The magnetic properties of Sm0.7Tb0.3FeO3 single crystal were studied in the temperature range from 3 to 400 K. A clear spin reorientation behavior with the gradual transition of the Fe3+ magnetic moment ordering from {Gz,Fx}-type ordering at low t...

We present a femtosecond spectroscopic magneto-optical investigation of the coherent and incoherent spin dynamics in the antiferromagnetic dielectric KNiF3. The pathways of the photoinduced energy flow to spins were controlled by tuning the pump photon energy. In particular, we demonstrate that laser pulses, with photon energy tuned to a nearly-zer...

The ability of a femtosecond laser pulse to manipulate and reverse the magnetization in a ferrimagnetic Gd24Fe66.5Co9.5 thin film was studied experimentally as a function of temperature. For a fixed energy of the laser pulse, the dynamics of magnetization showed different behavior depending on whether the sample temperature was below or above the m...

Bulk holmium iron garnet Ho3Fe5O12 is a cubic ferrimagnet with Curie temperature TC = 567 K and magnetization compensation point in the range 130–140 K. The magneto-optical data are presented for a holmium iron garnet Ho3Fe5O12 film, ∼10 μm thick, epitaxially grown on a (111)-type gadolinium-gallium garnet Gd3Ga5O12 substrate. A specific feature of...

Laser-induced ultrafast demagnetization in ferrimagnetic Gd x Fe 100−x−y Co y thin films was studied experimen-tally as a function of Gd concentration (x = 18, 22, 24, 30%, and y ≈ 9–10%), pump fluence, and sample temperature. The results showed that the conditions for full demagnetization at the ultrafast time scale in Gd x Fe 100−x−y Co y thin me...

Time-resolved magneto-optical imaging of laser-excited rare-earth orthoferrite (SmPr)FeO3 demonstrates that a single 60 fs circularly polarized laser pulse is capable of creating a magnetic domain on a picosecond time scale with a magnetization direction determined by the helicity of light. Depending on the light intensity and sample temperature, p...