arXiv subjects

N. Yu. Frolov

Publications and source records attributed to N. Yu. Frolov.

4 recordsLinked to original sources

arXiv2026

Propagation of laser-generated GHz surface acoustic wavepackets in FeRh/MgO(001) below and above the antiferromagnetic-ferromagnetic phase transition

Magnetoacoustic devices that harness the strong coupling between acoustic waves and magnons have emerged as a promising platform for energy-efficient spintronics. Laser-generated pulsed surface acoustic waves (SAWs) are particularly attractive for such applications, offering broadband frequency content up to the gigahertz (GHz) range, remote excitation without lithographic patterning, and surface localization for efficient on-chip integration. In this work, we present a comprehensive experimental study of laser-generated SAW pulses in the Fe49Rh51/MgO(001) system. A thin film of the near-equiatomic FeRh alloy serves both as an opto-acoustic transducer and as a mechanical load that modulates SAW propagation. The antiferromagnetic to ferromagnetic phase transition in FeRh, occurring slightly above room temperature, is accompanied by abrupt changes in its elastic properties, enabling controlled modification of the SAW excitation efficiency and dispersion characteristics by tuning the sample temperature and laser fluence. Using 160 fs laser pulses for excitation and time-resolved Sagnac interferometry for detection, we evaluated key SAW parameters, including amplitude, spectral content, phase and group velocities, and their in-plane anisotropy. Particular emphasis is placed on the dispersion relation and its anisotropy, which govern the coherent interaction between phonons and magnons and are determined primarily by the FeRh film.

cond-mat.mtrl-sci↗

arXiv2025

Laser-generated GHz surface acoustic waves with tunable amplitude during the magnetostructural phase transition in FeRh thin films

Laser-generated surface acoustic waves (SAW) facilitate efficient information processing in modern spintronics and magnonics. The ability to tune the SAW parameters such as amplitude is crucial to achieve acoustic control over magnonic properties. Such tunability can be achieved in phasechanging magnetic materials that accommodate both spin waves and SAWs. A promising material is the FeRh alloy, a metallic antiferromagnet at room temperature that undergoes a phase transition to the ferromagnetic state accompanied by a crystal lattice expansion at 370 K. This transition can also be induced by femtosecond laser pulses. In this paper, we use the phase transition in a 60 nm Fe49Rh51 film to optically generate pulses of Gigahertz quasi-Rayleigh SAWs. We detect them via the photoelastic effect and show that the lattice transformation during the phase transition is a dominant strain-generation mechanism for above-threshold excitation. The weight of this contribution rises as the sample is heated closer to the AFM-FM transition temperature and 'switches off' when heated above it, allowing for control of the SAW amplitude. A model based on thermodynamic parameters of Fe49Rh51 shows that the lattice transformation occurring within 95 ps effectively contributes to SAW generation happening on a comparable timescale, while non-equilibrium fast kinetics of the phase transition does not.

cond-mat.mtrl-sci↗

arXiv2025

Surface acoustic wave enabled all-optical determination of the interlayer elastic constants of van der Waals interface

Understanding the properties of two-dimensional materials interfaces with the substrate is necessary for device applications. Surface acoustic wave propagation through the layered material flake on a substrate could provide unique information on the transverse rigidity of the flake-to-substrate interaction. We generate ultrasonic waves by a focused femtosecond laser pulse at the surface of the model system -- fused silica with h-BN flake transferred above. Using an all-optical spatially resolved pump-probe interferometric technique, we measure the spatial dependencies of the surface vertical velocity profiles. Our measurements reveal the appearance of the surface acoustic wave dispersion in the hBN flake region compared to fused silica surface. Multilayer modeling allows us to gain access to longitudinal and shear elastic coupling constants $c^*_{33}$ and $c^*_{44}$ between hexagonal BN and substrate.

cond-mat.mtrl-sci↗

arXiv2021

3D Hypersound Microscopy of Van der Waals Heterostructures

We employ here a picosecond ultrasonic technique to study Van der Waals heterostructures. Temporal variation of the reflection coefficient of the Al film that covers Van der Waals hBN/WSe$_2$/hBN heterostructures on a sapphire substrate after the femtosecond laser pulse excitation is carefully measured using an interferometric technique with spatial resolution. The laser pulse generates a broadband sound wave packet in aluminum film propagating perpendicular to the plane direction and partially reflecting from the heterostructural interfaces. The demonstrated technique has enough sensitivity to resolve a WSe$_2$ monolayer embedded in hBN. We apply a multilayered model of the optical and acoustical response that allows to evaluate the mechanical parameters, in particular, rigidity of interfaces, inaccessible from the other measurements. Mapping of the Fourier spectra of the response clearly visualizes different composition regions and can therefore serve as an acoustic tomography tool. Our findings demonstrate almost zero acoustic phonon dissipation below 150 GHz at the interfaces and in the layers that makes Van der Waals heterostructures perspective for nano-acoustical applications.

cond-mat.mes-hall↗