arXiv subjects

Matthias Küß

Publications and source records attributed to Matthias Küß.

6 recordsLinked to original sources

arXiv2026

Phase-resolved imaging of coherent phonon-magnon coupling

We use a direct phase-resolved optical technique to study the coherence of spin waves (SWs) that are driven by surface acoustic waves (SAWs) via resonant magnetoelastic coupling. For this, we employ a piezoelectric lithium tantalate (LiTaO$_{3}$) substrate, equipped with micropatterned interdigital transducers for SAW excitation, which interact with SWs in a 5 nm thin and 20 $μ$m wide Co$_{40}$Fe$_{40}$B$_{20}$-waveguide. We detect the SAW and the SW using a phase-locked micro-focused optical polarization detection experiment and use the characteristic polarization dependence to separate the SAW and SW signals. Our measurements directly image the resonant and coherent excitation of the SW by the SAW.

cond-mat.mes-hall↗

arXiv2026

Magnetically Programmable Surface Acoustic Wave Filters: Device Concept and Predictive Modeling

Filtering surface acoustic wave (SAW) signals of specified frequencies depending on the strength of an external magnetic field in a magnetostrictive material has garnered significant interest due to its potential scientific and industrial applications. Here, we propose a device that achieves selective SAW attenuation by instead programming its internal magnetic state. To this end, we perform micromagnetic simulations for the magnetoelastic interaction of the Rayleigh SAW mode with spin waves (SWs) in exchange-decoupled Co/Ni islets on a piezoelectric LiTaO$_3$ substrate. Due to the islets exhibiting perpendicular magnetic anisotropy, the stray-field interaction between them leads to a shift in the SW dispersion depending on the magnetic alignment of neighboring islets. This significantly changes the efficiency of the magnetoelastic interaction at specified frequencies. We predict changes in SAW transmission of 52.0 dB/mm at 3.8 GHz depending on the state of the device. For the efficient simulation of the device, we extend a prior energy conservation argument based on analytical solutions of the SW to finite-difference numerical calculations, enabling the modeling of arbitrary magnetization patterns like the proposed islet-based design.

cond-mat.mes-hall↗

arXiv2026

Hematite Thin Films Grown on Z-Cut and Y-Cut Lithium Niobate Piezoelectric Substrates by Pulsed Laser Deposition

Altermagnets are a newly identified class of materials that combine advantageous characteristics of both ferro- and antiferromagnets, making them highly promising for spintronic applications. Hematite has recently been identified as an altermagnetic material and exhibits several noteworthy properties, including a high Néel temperature, a temperature dependent spin reorientation transition (SRT) at the Morin temperature ($T_\mathrm{M}$), and low magnetic damping. In this work, we demonstrate the epitaxial growth of hematite thin films on y- and z-cut lithium niobate (LiNbO$_3$) substrates using pulsed laser deposition (PLD). LiNbO$_3$ as piezoelectric substrate is of particular interest as it enables the efficient excitation of surface acoustic waves (SAWs) with interdigital transducers. The different substrate cuts allow for different orientations of the Néel vector. Films grown on y-cut LiNbO3 are single-crystalline and single-phase, while those deposited on z-cut LiNbO$_3$ exhibit two distinct in-plane (ip) domains rotated 60° relative to each other. On both substrates, the hematite thin films exhibit a temperature dependent SRT which allows the antiferromagnetic Néel vector to be controlled. This study paves the way for the development of high-quality piezoelectric/altermagnetic hyprids for magnonics and spintronics.

cond-mat.mtrl-sci↗

arXiv2025

Modeling Magnetoelastic Wave Interactions in Magnetic Films and Heterostructures: A finite-difference approach

The (inverse) magnetostrictive effect in ferromagnets couples the magnetic properties to the mechanical stress, allowing for an interaction between the magnetic and mechanical degrees of freedom. In this work, we present a time-integration scheme for the self-consistent simulation of coupled magnetoelastic dynamics within the framework of finite-difference micromagnetism. The proposed implementation extends the Landau-Lifshitz-Gilbert equation by a strain-induced effective field and concurrently solves the elastic equation of motion, while correctly incorporating stress and strain discontinuities at material interfaces. We then present a comprehensive set of examples, ranging from static stress configurations over material boundaries to simulations of surface acoustic wave attenuation in magnetically structured thin and thick films. These computational experiments both validate the implementation and underscore the importance of properly handling jump and boundary conditions in magnon-phonon interaction studies.

physics.comp-ph↗

arXiv2023

Coherent phonon-magnon interactions detected by micro-focused Brillouin light scattering spectroscopy

We investigated the interaction of surface acoustic waves and spin waves with spatial resolution by micro-focused Brillouin light scattering spectroscopy in a Co$_{40}$Fe$_{40}$B$_{20}$ ferromagnetic layer on a LiNbO$_{3}$-piezoelectric substrate. We experimentally demonstrate that the magnetoelastic excitation of magnons by phonons is coherent by studying the interfering BLS-signals of the phonons and magnons during their conversion process.We find a pronounced spatial dependence of the phonon annihilation and magnon excitation which we map as a function of the magnetic field. The coupling efficiency of the surface acoustic waves (SAWs) and the spin waves (SWs) is characterized by a magnetic field dependent decay of the SAWs amplitude.

physics.app-ph↗

arXiv2020

Nonreciprocal Dzyaloshinskii-Moriya magnetoacoustic waves

We study the interaction of surface acoustic waves with spin waves in ultra-thin CoFeB/Pt bilayers. Due to the interfacial Dzyaloshinskii-Moriya interaction (DMI), the spin wave dispersion is non-degenerate for oppositely propagating spin waves in CoFeB/Pt. In combination with the additional nonreciprocity of the magnetoacoustic coupling itself, highly nonreciprocal acoustic wave transmission through the magnetic film is observed. We systematically characterize the magnetoacoustic wave propagation in a thickness series of CoFeB($d$)/Pt samples as a function of magnetic field magnitude and direction, and at frequencies up to 7 GHz. We quantitatively model our results to extract the strength of the DMI and magnetoacoustic driving fields.

cond-mat.mes-hall↗