arXiv subjects

A. Thiaville

Publications and source records attributed to A. Thiaville.

At least 19 recordsLinked to original sources

arXiv2025

Crossover from Universal Depinning to Free Domain-Wall Dynamics in Ultrathin Iron Garnet Films

Magnetic domain walls display universal, disorder-controlled elastic dynamics at low drive, and texture-governed free motion at high drive. Here, we establish the crossover mechanism between these two regimes. Using experiments in ultrathin epitaxial iron garnet films and Landau-Lifshitz-Gilbert simulations, including disorder, thermal, and internal texture effects, we uncover a disorder- and temperature-dependent precessional flow that bridges pinned and free dynamics. We further demonstrate that the exceptionally low pinning in garnets arises from the weak coupling between domain walls and disorder, together with a correlation length that exceeds the wall width.

cond-mat.other↗

arXiv2025

Dzyaloshinskii-Moriya interaction in Fe5GeTe2 epitaxial thin films

Van der Waals ferromagnets, such as Fe5GeTe2, offer a promising platform for spintronic devices based on chiral magnetic textures, provided a significant Dzyaloshinskii-Moriya interaction (DMI) can be induced to stabilise the textures. Here, we directly measure DMI in epitaxial Fe5GeTe2 thin films using Brillouin light scattering spectroscopy and observe a consistent DMI (D=0.04 mJ/m2) across various thicknesses. Its weak thickness dependence, combined with the nominally symmetric film interfaces, suggests a bulk origin. Although we do not determine the microscopic mechanism, our findings are compatible with ab initio calculations linking DMI to partial ordering of Fe split sites. Additionally, we find a low magnetic dissipation (alpha<0.02). The observed DMI, which could be further enhanced by optimising the Fe site ordering, combined with low dissipation, makes Fe5GeTe2 a strong candidate for exploring the dynamics of chiral magnetic textures in two-dimensional materials.

cond-mat.mtrl-sci↗

arXiv2024

Spin-Wave-Assisted Thermal Reversal of Epitaxial Perpendicular Magnetic Nanodots

The magnetic susceptibility of self-organized two-dimensional Co nanodots on Au(111) has been measured as a function of their size in the 2-7~nm diameter range. We show that the activation energy for the thermal reversal displays a power law behavior with the dot volume. Atomic scale simulations based on the Heisenberg hamiltonian show that this behavior is due to a deviation from the macrospin model for dot size as small as 3~nm in diameter. This discrepancy is attributed to finite temperature effects through the thermal excitation of spin-wave modes inside the particles

cond-mat.mes-hall↗

arXiv2021

Magnetic domain wall dynamics in the precessional regime: influence of the Dzyaloshinskii-Moriya interaction

The domain wall dynamics driven by an out of plane magnetic field was measured for a series of magnetic trilayers with different strengths of the interfacial Dzyaloshinskii-Moriya interaction (DMI). The features of the field-driven domain wall velocity curves strongly depend on the amplitude of the HD field stabilising chiral Néel walls. The measured Walker velocity, which in systems with large DMI is maintained after the Walker field giving rise to a velocity plateau up to the Slonczewski field HS, can be easily related to the DMI strength. Yet, when the DMI field HD and the domain wall demagnetising field HDW have comparable values, a careful analysis needs to be done in order to evaluate the impact of the DMI on the domain wall velocity. By means of a one-dimensional model and 2D simulations, we successfully extend this method to explain experimental results to cases where HD and HDW are comparable.

cond-mat.mes-hall↗

arXiv2021

Staggered spin-orbit interaction in a nanoscale device

The coupling of the spin and the motion of charge carriers stems directly from the atomic structure of a conductor. It has become an important ingredient for the emergence of topological matter, and, in particular, topological superconductivity which could host non-abelian excitations such as Majorana modes or parafermions. These modes are sought after mostly in semiconducting platforms which are made of heavy atoms and therefore exhibit naturally a large spin-orbit interaction. Creating domain walls in the spin orbit interaction at the nanoscale may turn out to be a crucial resource for engineering topological excitations suitable for universal topological quantum computing. For example, it has been proposed for exploring exotic electronic states or for creating hinge states. Realizing this in natural platforms remains a challenge. In this work, we show how this can be alternatively implemented by using a synthetic spin orbit interaction induced by two lithographically patterned magnetically textured gates. By using a double quantum dot in a light material -- a carbon nanotube -- embedded in a microwave cavity, we trigger hopping between two adjacent orbitals with the microwave photons and directly compare the wave functions separated by the domain wall via the light-matter coupling. We show that we can achieve an engineered staggered spin-orbit interaction with a change of strength larger than the hopping energy between the two sites.

cond-mat.mes-hall↗

arXiv2020

Strength and length-scale of the interaction between domain walls and pinning disorder in thin ferromagnetic films

We explore the magnetic-field-driven motion of domain walls with different chiralities in thin ferromagnetic films made of Pt/Co/Pt, Au/Co/Pt, and Pt/Co/Au. From the analysis of domain wall dynamics, we extract parameters characterizing the interaction between domain walls and weak pinning disorder of the films. The variations of domain wall structure, controlled by an in-plane field, are found to modify the characteristic length-scale of pinning in strong correlation with the domain wall width, whatever its chirality and the interaction strength between domain walls and pinning defects. These findings should be also relevant for a wide variety of elastic interfaces moving in weak pinning disordered media.

cond-mat.mes-hall↗

arXiv2019

Study of the velocity plateau of Dzyaloshinskii domain walls

We study field-driven domain wall (DW) velocities in asymmetric multilayer stacks with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction (DMI), both experimentally and by micromagnetic simulations. Using magneto-optical Kerr microscopy under intense and nanoseconds-long fields, we show that DWs in these films propagate at velocities up to hundreds of m/s and that, instead of the expected decrease of velocity after the Walker field, a long plateau with constant velocity is observed, before breakdown. Both the maximum speed and the field extent of the velocity plateau strongly depend on the values of the spontaneous magnetization and the DMI strength, as well as on the magnetic anisotropy. Micromagnetic simulations reproduce these features in sufficiently wide strips, even for perfect samples. A physical model explaining the microscopic origin of the velocity plateau is proposed.

cond-mat.mes-hall↗

arXiv2019

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures has emerged as a powerful tool to generate complex magnetic textures, interconvert charge and spin under applied current, and control magnetization dynamics. Current-induced spin-orbit torques mediate the transfer of angular momentum from the lattice to the spin system, leading to sustained magnetic oscillations or switching of ferromagnetic as well as antiferromagnetic structures. The manipulation of magnetic order, domain walls and skyrmions by spin-orbit torques provides evidence of the microscopic interactions between charge and spin in a variety of materials and opens novel strategies to design spintronic devices with potentially high impact in data storage, nonvolatile logic, and magnonic applications. This paper reviews recent progress in the field of spin-orbitronics, focusing on theoretical models, material properties, and experimental results obtained on bulk noncentrosymmetric conductors and multilayer heterostructures, including metals, semiconductors, and topological insulator systems. Relevant aspects for improving the understanding and optimizing the efficiency of nonequilibrium spin-orbit phenomena in future nanoscale devices are also discussed.

cond-mat.mes-hall↗

arXiv2019

Synthetic spin orbit interaction for Majorana devices

The interplay of superconductivity with a non-trivial spin texture holds promises for the engineering of non-abelian Majorana quasi-particles. A wide class of systems expected to exhibit exotic correlations are based on nanoscale conductors with strong spin-orbit interaction, subject to a strong external magnetic field. The strength of the spin-orbit coupling is a crucial parameter for the topological protection of Majorana modes as it forbids other trivial excitations at low energy. The spin-orbit interaction is in principle intrinsic to a material. As a consequence, experimental efforts have been recently focused on semiconducting nano-conductors or spin-active atomic chains contacted to a superconductor. Alternatively, we show how both a spin-orbit and a Zeeman effect can be autonomously induced by using a magnetic texture coupled to any low dimensional conductor, here a carbon nanotube. Transport spectroscopy through superconducting contacts reveals oscillations of Andreev like states under a change of the magnetic texture. These oscillations are well accounted for by a scattering theory and are absent in a control device with no magnetic texture. A large synthetic spin-orbit energy of about 1.1 meV, larger than the intrinsic spin orbit energy in many other platforms, is directly derived from the number of oscillations. Furthermore, a robust zero energy state, the hallmark of devices hosting localized Majorana modes, emerges at zero magnetic field. Our findings synthetize all the features for the emergence of Majorana modes at zero magnetic field in a controlled, local and autonomous fashion. It could be used for advanced experiments, including microwave spectroscopy and braiding operations, which are at the heart of new schemes of topological quantum computation.

cond-mat.mes-hall↗

arXiv2018

Current-induced nucleation and dynamics of skyrmions in a Co-based Heusler alloy

We demonstrate room-temperature stabilization of dipolar magnetic skyrmions with diameters in the range of $100$ nm in a single ultrathin layer of the Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy magnetometer operating in the photoluminescence quenching mode. We first demonstrate skyrmion nucleation by spin-orbit torque and show that its efficiency can be significantly improved using tilted magnetic fields, an effect which is not specific to Heusler alloys and could be advantageous for future skyrmion-based devices. We then show that current-induced skyrmion motion remains limited by strong pinning effects, even though CFA is a magnetic material with a low magnetic damping parameter.

cond-mat.mtrl-sci↗

arXiv2017

Skyrmion morphology in ultrathin magnetic films

Nitrogen-vacancy magnetic microscopy is employed in quenching mode as a non-invasive, high resolution tool to investigate the morphology of isolated skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to be strongly affected by local pinning effects and magnetic field history. Micromagnetic simulations including static disorder, based on a physical model of grain-to-grain thickness variations, reproduce all experimental observations and reveal the key role of disorder and magnetic history in the stabilization of skyrmions in ultrathin magnetic films. This work opens the way to an in-depth understanding of skyrmion dynamics in real, disordered media.

cond-mat.mtrl-sci↗

arXiv2017

Making the Dzyaloshinskii-Moriya interaction visible

Brillouin light spectroscopy is a powerful and robust technique for measuring the interfacial Dzyaloshinskii-Moriya interaction in thin films with broken inversion symmetry. Here we show that the magnon visibility, i.e. the intensity of the inelastically scattered light, strongly depends on the thickness of the dielectric seed material - SiO$_2$. By using both, analytical thin-film optics and numerical calculations, we reproduce the experimental data. We therefore provide a guideline for the maximization of the signal by adapting the substrate properties to the geometry of the measurement. Such a boost-up of the signal eases the magnon visualization in ultrathin magnetic films, speeds-up the measurement and increases the reliability of the data.

cond-mat.mtrl-sci↗

arXiv2017

The interfacial nature of proximity induced magnetism and the Dzyaloshinskii-Moriya interaction at the Pt/Co interface

The Dzyaloshinskii-Moriya interaction (DMI) has been shown to stabilise Neél domain walls in magnetic thin films, allowing high domain wall velocities driven by spin current effects. DMI occurs at the interface between ferromagnetic and heavy metal layers with strong spin-orbit coupling, but details of the interaction remain to be understood and the role of proximity induced magnetism (PIM) in the heavy metal is unknown. We report interfacial DMI and PIM in Pt determined as a function of Au and Ir spacer layers in Pt/Co/Au,Ir/Pt. The length-scale for both interactions is sensitive to sub-nanometre changes in the spacer thickness, and they correlate over sub mono-layer spacer thicknesses, but not for thicker spacers. The spacer layer thickness dependence of the Pt PIM for both Au and Ir shows a rapid monotonic decay, while the DMI changes rapidly but has a two-step approach to saturation and continues to change, even after the PIM is lost.

cond-mat.mtrl-sci↗

arXiv2016

Path to collapse for an isolated Néel skyrmion

A path method is implemented in order to precisely and generally describe the collapse of isolated skyrmions in a Co/Pt(111) monolayer, on the basis of atomic scale simulations. Two collapse mechanisms with different energy barriers are found. The most obvious path, featuring a homogeneous shrinking gives the largest energy, whereas the lowest energy barrier is shown to comply with the outcome of Langevin dynamics under a destabilizing field of 0.25 T, with a lifetime of 20~ns at around 80~K. For this lowest energy barrier path, skyrmion destabilization occurs much before any topology change, suggesting that topology plays a minor role in the skyrmion stability. On the contrary, an important role appears devoted to the Dzyaloshinskii-Moriya interaction, establishing a route towards improved skyrmion stability.

cond-mat.mes-hall↗

arXiv2016

Direct measurement of interfacial Dzyaloshinskii-Moriya interaction in X/CoFeB/MgO heterostructures with a scanning-NV magnetometer

The Dzyaloshinskii-Moriya Interaction (DMI) has recently attracted considerable interest owing to its fundamental role in the stabilization of chiral spin textures in ultrathin ferromagnets, which are interesting candidates for future spintronic technologies. Here we employ a scanning nano-magnetometer based on a single nitrogen-vacancy (NV) defect in diamond to locally probe the strength of the interfacial DMI in CoFeB/MgO ultrathin films grown on different heavy metal underlayers X=Ta,TaN, and W. By measuring the stray field emanating from DWs in micron-long wires of such materials, we observe deviations from the Bloch profile for TaN and W underlayers that are consistent with a positive DMI value favoring right-handed chiral spin structures. Moreover, our measurements suggest that the DMI constant might vary locally within a single sample, illustrating the importance of local probes for the study of magnetic order at the nanoscale.

cond-mat.mes-hall↗

arXiv2016

Very large domain wall velocities in Pt/Co/Gd trilayers with Dzyaloshinskii-Moriya interaction

We carried out measurements of domain wall (DW) velocities driven by magnetic field pulses in symmetric Pt/Co/Pt and asymmetric Pt/Co/AlOx, Pt/Co/GdOx and Pt/Co/Gd trilayers with ultrathin Co layers and perpendicular magnetic anisotropy. In agreement with theoretical models, the maximum observed velocity is much larger in the asymmetric samples, where the interfacial Dzyaloshinskii-Moriya interaction (DMI) stabilises chiral Néel walls, than in the symmetric stack. In addition, in Pt/Co/Gd very large DW speeds (up to 600 m/s) are obtained, 2.5 times larger than in samples with oxidised Gd. Magnetic measurements reveal that this may be explained by the anti-parallel coupling between the magnetic moments of Gd and Co at the Gd/Co interface, leading to a decrease of the total magnetisation. In quantitative agreement with analytical models, in all samples the maximum observed DW speed scales as D=Ms, where D is the strength of the DMI and Ms the spontaneous magnetisation.

cond-mat.mes-hall↗

arXiv2015

Velocity asymmetry of Dzyaloshinskii domain walls in the creep and flow regimes

We have carried out measurements of domain wall dynamics in a Pt/Co/GdOx(t) wedge sample with perpendicular magnetic anisotropy. When driven by an easy-axis field Hz in the presence of an in-plane field Hx, the domain wall expansion along x is anisotropic, as expected for samples presenting Dzyaloshinskii-Moriya interaction. In the creep regime, the sign and the value of the domain wall velocity asymmetry changes along the wedge. We show that in our samples the domain wall speed vs. Hx curves in the creep regime cannot be explained simply in terms of the variation of the domain wall energy with Hx, as suggested by previous works. For this reason the strength and the sign of the Dzyaloshinskii-Moriya interaction (DMI) cannot be extracted from these measurements. To obtain reliable information on the DMI strength using magnetic field-induced domain wall dynamics, measurements have been performed with high fields, bringing the DW close to the flow regime of propagation. In this case, the large values of DMI are coherent with those obtained from current-driven domain wall dynamics.

cond-mat.mtrl-sci↗

arXiv2014

The nature of domain walls in ultrathin ferromagnets revealed by scanning nanomagnetometry

The recent observation of current-induced domain wall (DW) motion with large velocity in ultrathin magnetic wires has opened new opportunities for spintronic devices. However, there is still no consensus on the underlying mechanisms of DW motion. Key to this debate is the DW structure, which can be of Bloch or Néel type, and dramatically affects the efficiency of the different proposed mechanisms. To date, most experiments aiming to address this question have relied on deducing the DW structure and chirality from its motion under additional in-plane applied fields, which is indirect and involves strong assumptions on its dynamics. Here we introduce a general method enabling direct, in situ, determination of the DW structure in ultrathin ferromagnets. It relies on local measurements of the stray field distribution above the DW using a scanning nanomagnetometer based on the Nitrogen-Vacancy defect in diamond. We first apply the method to a Ta/Co40Fe40B20(1 nm)/MgO magnetic wire and find clear signature of pure Bloch DWs. In contrast, we observe left-handed Néel DWs in a Pt/Co(0.6 nm)/AlOx wire, providing direct evidence for the presence of a sizable Dzyaloshinskii-Moriya interaction (DMI) at the Pt/Co interface. This method offers a new path for exploring interfacial DMI in ultrathin ferromagnets and elucidating the physics of DW motion under current.

cond-mat.mes-hall↗