arXiv subjects

André Thiaville

Publications and source records attributed to André Thiaville.

At least 19 recordsLinked to original sources

arXiv2026

Reprogrammable magnonic logic in a multiferroic heterostructure via magnetoelectric coupling

The realization of fully reconfigurable, voltage-controlled, and programmable on-chip magnonic devices is essential to fully harness the potential of spin waves for signal processing, logic and neuromorphic computing. Yet, existing demonstrations of electrical tuning of magnonic responses are either volatile, current-driven and thus energy-inefficient, or rely on local strain modification limiting their scalability for wafer-scale integration. Here, we address this challenge using a BiFeO3/La0.67Sr0.33MnO3 multiferroic thin film heterostructure. We show that ferroelectric domain engineering in BiFeO3 enables deterministic tuning of the magnon dispersion of La0.67Sr0.33MnO3, producing frequency shifts up to $\sim 150 MHz$ and allowing reconfigurable waveguiding. Micro-focused Brillouin light scattering directly images these effects, revealing electrically defined magnonic waveguides and spatially programmable dispersion. Compared to conventional approaches, this method provides non-volatile and reversible control. Furthermore, using an inverse-design simulation code, we demonstrate the capability of our platform to perform advanced magnonic functions such as frequency demultiplexing. Our results open a new avenue for using magnetoelectric heterostructures for magnonic logic, with further applicability to reservoir and neuromorphic computing and AI driven magnonic devices.

cond-mat.mes-hall↗

arXiv2025

Experimental determination and micromagnetic analysis of spin wave modes in cylindrical nanowires

We report an experimental study of spin wave modes in individual cylindrical nanowires, a textbook situation of confined spin waves in 3D nanomagnetism. We observe discrete modes of thermal spin waves with micro-Brillouin light scattering, whose frequencies $f$ shift to higher values as the applied longitudinal induction magnetic field $B_z$ increases. Micromagnetic simulations allowed us to associate every $f(B_z)$ curve to a given spatial mode, labeled with radial and azimuthal indices $\ell$ and $m$.

cond-mat.mes-hall↗

arXiv2025

Effects of antiferromagnetic coupling and pinning on domain wall dynamics in synthetic ferrimagnets

Domain wall (DW) dynamics in antiferromagnetic (AFM) systems offer the advantages over their ferromagnetic counterparts of having faster and more energy efficient manipulation due to the absence of net magnetization, leading to reduced magnetic crosstalk and improved performance in spintronic devices. A comprehensive analysis of DW dynamics across regimes such as creep, depinning, and flow is well established in ferromagnetic systems but remains lacking in AFM-coupled systems. In this study, we explore the nature of DW dynamics in synthetic ferrimagnetic multilayers composed of Pt|Co|Tb|Al for different Tb thickness, focusing on the underlying pinning parameters, and on the different regimes of DW dynamics driven by spin-orbit torques (SOTs). We find that due to the AFM coupling between Co and Tb, the magnetic moment of Tb increases with Tb thickness resulting in a reduced saturation magnetization and an enhanced depinning field. The DW disorder interaction is found to vary weakly with the AFM coupling between Co and Tb, while the complete withdrawal of the Tb layer strongly increases the anisotropy and the DW pinning. Furthermore, we propose a novel approach to measure effective SOTs by comparing depinning transitions in current and field-induced DW motion. This research reveals new insights into DW dynamics in coupled AFM systems, highlighting enhancements in mobility through optimized SOTs and pinning landscapes.

cond-mat.other↗

arXiv2024

Interfacial spin-orbitronic effects controlled with different oxidation levels at the Co|Al interface

Perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interactions are key interactions in modern spintronics. These interactions are thought to be dominated by the oxidation of the Co|Al interface in the archetypal Platinum-Cobalt-Aluminum oxide system. Here, we observe a double sign change in the anisotropy and about threefold variation in interfacial chiral interaction, influenced not only by the oxidation, but also by the metallic Al thickness. Contrary to previous assumptions about negligible spin-orbit effects at light metal interfaces, we not only observe strong PMA with fully oxidized Al, decreasing and turning negative (in-plane) with less oxygen at the Co|Al interface, we also observe that the magnetic anisotropy reverts to positive (out-of-plane) values at fully metallic Co|Al interface. These findings suggest modification in Co d band via Co|Al orbital hybridization, an effect supported by X-ray absorption spectroscopy and ab initio theory calculations, highlighting the key impact of strain on interfacial mechanisms at fully metallic Co|Al interface.

cond-mat.mtrl-sci↗

arXiv2023

Driving skyrmions in flow regime in synthetic ferrimagnets

Despite significant advances in the last decade regarding the room temperature stabilization of skyrmions or their current induced dynamics, the impact of local material inhomogeneities still remains an important issue that impedes to reach the regime of steady state motion of these spin textures. Here, we study the spin-torque driven motion of skyrmions in synthetic ferrimagnetic multilayers with the aim of achieving high mobility and reduced skyrmion Hall effect. We consider Pt|Co|Tb multilayers of various thicknesses with antiferromagnetic coupling between the Co and Tb magnetization. The increase of Tb thickness in the multilayers allows to reduce the total magnetic moment and increases the spin-orbit torques allowing to reach velocities up to 400 m.s-1 for skyrmions with diameters of about 160 nm. We demonstrate that due to reduced skyrmion Hall effect, combined with the edge repulsion of the magnetic track making the skyrmions moving along the track without any transverse deflection. Further, by comparing the field-induced domain wall motion and current-induced skyrmion motion, we demonstrate that the skyrmions at the largest current densities present all the characteristics of a dynamical flow regime.

cond-mat.mtrl-sci↗

arXiv2023

Evidence of Strong Dzyaloshinskii-Moriya Interaction at the Cobalt/Hexagonal Boron Nitride Interface

The Dzyaloshinskii-Moriya interaction (DMI) and perpendicular magnetic anisotropy (PMA) were measured on four series of Co films (1-2.2 nm thick) grown on Pt or Au and covered with h-BN or Cu. Clean h-BN/Co interfaces were obtained by exfoliating h-BN and transferring it onto the Co film in situ in the ultra-high-vacuum evaporation chamber. By comparing h-BN and Cu-covered samples, the DMI induced by the Co/h-BN interface was extracted and found to be comparable in strength to that of the Pt/Co interface, one of the largest known values. The strong observed DMI despite the weak spin-orbit interaction in h-BN supports a Rashba-like origin in agreement with recent theoretical results. Upon combination of it with Pt/Co in Pt/Co/h-BN heterostructures, even stronger PMA and DMI are found which stabilizes skyrmions at room temperature and a low magnetic field.

cond-mat.mtrl-sci↗

arXiv2023

From Early Theories of Dzyaloshinskii-Moriya Interactions in Metallic Systems to Today's Novel Roads

Since the early 1960's, the discovery of Dzyaloshinskii-Moriya interaction (DMI) helped to explain the physical mechanisms behind certain magnetic phenomena, such as net moment in antiferromagnets, or enhanced anisotropy field from heavy metals impurity in dilute Cu:Mn alloy. Since the researchers unveil the key role that DMI plays in stabilizing chiral Neel type magnetic domain wall and magnetic skyrmions, the studies on DMI have received growing interest. Governed by spin-orbit coupling (SOC) and various types of inversion symmetry breaking (ISB) in magnetic systems, DMI drives the forming of distinct morphologies of magnetic skyrmions. Our aim is to briefly introduce the research history of DMI and its significance in the field of modern spintronics.

cond-mat.mtrl-sci↗

arXiv2023

Improving Néel domain walls dynamics and skyrmion stability using He ion irradiation

Magnetization reversal and domain wall dynamics in Pt/Co/AlOx trilayers have been tuned by He+ ion irradiation. Fluences up to 1.5x10$^{15}$ ions/cm$^2$ strongly decrease the perpendicular magnetic anisotropy (PMA), without affecting neither the spontaneous magnetization nor the strength of the Dzyaloshinskii-Moriya interaction (DMI). This confirms the robustness of the DMI interaction against interfacial chemical intermixing, already predicted by theory. In parallel with the decrease of the PMA in the irradiated samples, a strong decrease of the depinning field is observed. This allows the domain walls to reach large maximum velocities with lower magnetic fields with respect to those needed for the pristine films. Decoupling PMA from DMI can therefore be beneficial for the design of low energy devices based on domain wall dynamics. When the samples are irradiated with larger He+ fluences, the magnetization gets close to the out-of-plane/in-plane reorientation transition where 100nm size magnetic skyrmions are stabilized. We observe that as the He+ fluence increases, the skyrmion size decreases while these magnetic textures become more stable against the application of an external magnetic field.

cond-mat.mtrl-sci↗

arXiv2023

Field-free switching of perpendicular magnetization in an ultrathin epitaxial magnetic insulator

For energy efficient and fast magnetic memories, switching of perpendicular magnetization by the spin-orbit torque (SOT) appears as a very promising solution, even more using magnetic insulators that suppress electrical shunting. This SOT switching generally requires the assistance of an in-plane magnetic field to break the symmetry. Here, we present experiments demonstrating the field-free SOT switching of perpendicularly magnetized layers of the thulium iron garnet (Tm_{3}Fe_{5}O_{12}) magnetic insulator. The polarity of the switching loops, clockwise (CW) or counter-clockwise (CCW), is determined by the direction of the initial current pulses, in contrast with field-assisted switchings in which this polarity is controlled by the direction of the field. After an independent determination of Dzyaloshinskii-Moriya interaction (DMI), we relate the field free switching to the interplay of SOT and DMI and the polarity of the loops to the imprint of a Néel domain wall induced by the first pulse, in agreement with Kerr imaging. Our observation and interpretation of field-free electrical switching of a magnetic insulator is an important milestone for future low power spintronic devices.

physics.app-ph↗

arXiv2023

Driving skyrmions with low threshold current density in Pt/CoFeB thin film

Magnetic skyrmions are topologically stable spin swirling particle like entities which are appealing for next generation spintronic devices. The expected low critical current density for the motion of skyrmions makes them potential candidates for future energy efficient electronic devices. Several heavy metal/ferromagnetic (HM/FM) systems have been explored in the past decade to achieve faster skyrmion velocity at low current densities. In this context, we have studied Pt/CoFeB/MgO heterostructures in which skyrmions have been stabilized at room temperature (RT). It has been observed that the shape of the skyrmions are perturbed even by the small stray field arising from low moment magnetic tips while performing the magnetic force microscopy (MFM), indicating presence of low pinning landscape in the samples. This hypothesis is indeed confirmed by the low threshold current density to drive the skyrmions in our sample, at velocities of few 10m/s.

cond-mat.mtrl-sci↗

arXiv2022

Revealing nanoscale disorder in W/CoFeB/MgO ultra-thin films using domain wall motion

Disorder in ultra-thin magnetic films can significantly hinder domain wall motion. One of the main issues on the path towards efficient domain wall based devices remains the characterization of the pinning landscape at the nanoscale. In this paper, we study domain wall motion in W/CoFeB/MgO thin films with perpendicular magnetic anisotropy crystallized by annealing at 400$^{\circ}$C and a process based on He$^{+}$ irradiation combined with elevated temperatures. Magnetic properties are similar for the whole series of samples, while the magnetic domain wall mobility is critically improved in the irradiated samples. By using an analytical model to extract nanoscale pinning parameters, we reveal important variations in the disorder of the crystallized samples. This work offers a unique opportunity to selectively analyze the effects of disorder on the domain wall dynamics, without the contribution of changes in the magnetic properties. Our results highlight the importance of evaluating the nanoscale pinning parameters of the material when designing devices based on domain wall motion, which in return can be a powerful tool to probe the disorder in ultra-thin magnetic films.

cond-mat.mtrl-sci↗

arXiv2021

Element-selective modulation of interfacial Dzyaloshinskii-Moriya interaction in Pt|Co|Metal based multilayers

Despite a decade of research, the precise mechanisms occurring at interfaces underlying the Dzyaloshinskii-Moriya interaction (DMI), and thus the possibility of fine-tuning it, are not yet fully identified. In this study, we investigate the origin of the interfacial DMI, aiming at disentangling how independent are the interfaces around the ferromagnetic layer, and what are their relative contributions to the effective DMI amplitude. For this purpose, we have grown and investigated a large variety of systems with a common structure Pt$|$Co$|M$ with $M =$ Ni, Pd, Ru, Al, Al$|$Ta and MoSi. We explore the correlation between the effective interfacial DMI, and different intrinsic properties of metals, namely atomic number, electronegativity and work function difference at the Co$|M$ interfaces. We find a linear relationship between interfacial DMI and the work function difference between the two elements, hence relating the nature of this behavior to the interfacial potential gradient at the metallic interfaces. The understanding of the DMI mechanism is of utmost importance since it opens up the possibility of precisely engineering the magnetic and hence the spintronic properties for future devices.

cond-mat.mtrl-sci↗

arXiv2021

Spin-orbit coupling in single layer ferrimagnets: direct observation of spin-orbit torques and chiral spin textures

We demonstrate that effects of spin-orbit coupling and inversion asymmetry exist in a single GdFeCo ferrimagnetic layer, even without a heavy metal interface. We use electric transport measurements to quantify the spin-orbit torques. We measure the Dzyaloshinskii-Moriya interaction using Brillouin light scattering measurement technique, and we observe the resulting chiral magnetic textures using x-ray PEEM microscopy. We attribute these effects to a composition variation along the thickness, that we observed by scanning transmission electron microscopy. We show that these effects can be optimized by varying the GdFeCo thickness or by combining them with interfacial effects.

cond-mat.mtrl-sci↗

arXiv2021

Chiral magnetic domain walls under transverse fields: a semi-analytical model

An analytical model for the domain wall structure in ultrathin films with perpendicular easy axis and interfacial Dzyaloshinskii-Moriya interaction, submitted to an arbitrary in-plane magnetic field, is presented. Its solution is simplified to the numerical minimization of an analytic function of just one variable. The model predictions are compared to numerical micromagnetic simulations, using parameters of existing samples, revealing a very good agreement. Remaining differences are analyzed, and partly corrected. Differences with the predictions of the simplest model, usually found in the literature, in which only the domain wall moment's in-plane orientation can vary, are exemplified. The model allows accurate computations, as a function of in-plane field module and orientation, of the domain wall tension and width, quantities controlling the creep motion of domain walls in such films.

cond-mat.mes-hall↗

arXiv2020

Domain wall propagation by spin-orbit torques in in-plane magnetized systems

The effect of damping-like spin-orbit torque (DL SOT) on magnetic domain walls (DWs) in in-plane magnetised soft tracks is studied analytically and with micromagnetic simulations. We find that DL SOT drives vortex DWs, whereas transverse DWs, the other typical DW structure in soft tracks, propagate only if the Dzyaloshinskii-Moriya interaction (DMI) is present. The SOT drive can add to, and be more efficient than, spin-transfer torque (STT), and so may greatly benefit applications that require in-plane DWs. Our analysis based on the Thiele equation shows that the driving force arises from a cycloidal distortion of the DW structure caused by geometrical confinement or DMI. This distortion is higher, and the SOT more efficient, in narrower, thinner tracks. These results show that the effects of SOT cannot be understood by simply considering the effective field at the center of the structure, an ill-founded but often-used estimation. We also show that the relative magnitude of STT and DL SOT can be determined by comparing the motion of different vortex DW structures in the same track.

cond-mat.mtrl-sci↗

arXiv2020

Current distribution in metallic multilayers from resistance measurements

The in-plane current profile within multilayers of generic structure Ta/Pt/(CoNi)/Pt/Ta is investigated. A large set of samples where the thickness of each layer is systematically varied was grown, followed by the measurement of the sheet resistance of each sample. The data are analyzed by a series of increasingly elaborate models, from a macroscopic engineering approach to mesoscopic transport theory. Non-negligible variations of the estimated repartition of current between the layers are found. The importance of having additional structural data is highlighted.

cond-mat.mtrl-sci↗

arXiv2018

Brownian motion of magnetic domain walls and skyrmions, and their diffusion constants

Extended numerical simulations enable to ascertain the diffusive behavior at finite temperatures of chiral walls and skyrmions in ultra-thin model Co layers exhibiting symmetric - Heisenberg - as well as antisymmetric - Dzyaloshinskii-Moriya - exchange interactions. The Brownian motion of walls and skyrmions is shown to obey markedly different diffusion laws as a function of the damping parameter. Topology related skyrmion diffusion suppression with vanishing damping parameter, albeit already documented, is shown to be restricted to ultra-small skyrmion sizes or, equivalently, to ultra-low damping coefficients, possibly hampering observation.

cond-mat.mes-hall↗

arXiv2018

Velocity enhancement by synchronization of magnetic domain walls

Magnetic domain walls are objects whose dynamics is inseparably connected to their structure. In this work we investigate magnetic bilayers, which are engineered such that a coupled pair of domain walls, one in each layer, is stabilized by a cooperation of Dzyaloshinskii-Moriya interaction and flux-closing mechanism. The dipolar field mediating the interaction between the two domain walls, links not only their position but also their structure. We show that this link has a direct impact on their magnetic field induced dynamics. We demonstrate that in such a system the coupling leads to an increased domain wall velocity with respect to single domain walls. Since the domain wall dynamics is observed in a precessional regime, the dynamics involves the synchronization between the two walls, to preserve the flux closure during motion. Properties of these coupled oscillating walls can be tuned by an additional in-plane magnetic field enabling a rich variety of states, from perfect synchronization to complete detuning.

cond-mat.mes-hall↗