arXiv subjects

Aloïs Arrighi

Publications and source records attributed to Aloïs Arrighi.

4 recordsLinked to original sources

arXiv2026

Emergent gold-induced interfacial magnetism in monolayer FePS$_3$

Owing to their atomically clean interfaces and extreme thinness, two-dimensional (2D) materials are ideal hosts for strong proximity effects, whereby contact with an adjacent material reshapes their ground state. Here, we demonstrate such an effect within a hybrid heterostructure, between the 2D antiferromagnet FePS$_3$ and an ultrathin gold film. Rather than a passive support, the latter profoundly changes the nature of the magnetism in the 2D magnet, inducing a sizeable interfacial moment. Large-area flakes from Au-assisted exfoliation, combined with element-selective X-ray absorption mapping, enable a layer-by-layer study from monolayer to bulk, benchmarked against an inert SiO$_2$ substrate reference. At 9 T and 5 K, the monolayer on gold shows a three-fold enhanced X-ray magnetic circular dichroism relative to SiO$_2$, with a $\sim$40% reduction of the orbital-to-spin moment ratio. Resonant inelastic X-ray scattering reveals a collapse of the crystal-field (d-d) excitations and a massive spectral-weight transfer to the charge-transfer region, unveiling the microscopic mechanism behind this change. Supported by atomic multiplet calculations, we identify interfacial charge transfer and Fe 3d-Au hybridization as the origin of these effects, which decay over the first three layers and vanish at the pentalayer, establishing layer number combined with substrate engineering as an atomically precise handle.

cond-mat.mtrl-sci↗

arXiv2025

Laser patterning of the room temperature van der Waals ferromagnet 1$T$-CrTe$_2$

Lamellar crystalline materials, whose layers are bond by van der Waals forces, can be stacked to form ultrathin artificial heterostructures, and in particular vertical magnetic junctions when some of the stacked materials are (ferro)magnetic. Here, using the room temperature van der Waals ferromagnet 1$T$-CrTe$_2$, we report a method for patterning lateral magnetic junctions. Exploiting the heat-induced phase transformation of the material into Cr$_x$Te$_y$ compounds ($x/y>1/2$), we use local laser heating to imprint patterns at the micron-scale. Optimizing laser heat dissipation, we further demonstrate the crucial role of the substrate to control the phase transformation. If plain, unstructured poorly heat-conducting substrates allow for direct writing of magnetic patterns, structured $h$-BN layers can serve as heat stencils to draw potentially thinner patterns. Besides, $h$-BN encapsulation turns out to be heat-protective (in addition from protecting against oxidation as it is generally used for), allowing the demonstration of room temperature ferromagnetism in $<$7~nm-thick 1$T$-CrTe$_2$.

cond-mat.mtrl-sci↗

arXiv2022

A simple KPFM-based approach for electrostatic-free topographic measurements: the case of MoS$_2$ on SiO$_2$

A simple implementation of Kelvin probe force microscopy is reported that enables recording topographic images in the absence of any component of the electrostatic force. Our approach is based on a close loop z-spectroscopy operated in data cube mode. Curves of the tip-sample distance as a function of time are recorded onto a 2D grid. A dedicated circuit holds the KPFM compensation bias and subsequently cut off the modulation voltage during well-defined time-windows within the spectroscopic acquisition. Topographic images are recalculated from the matrix of spectroscopic curves. This approach is applied to the case of transition metal dichalcogenides (TMD) monolayers grown by chemical vapour deposition on silicon oxide substrates. In addition, we check to what extent a proper stacking height estimation can also be performed by recording series of images for decreasing values of the bias modulation amplitude. The outputs of both approaches are shown to be fully consistent. The results exemplify how in the operating conditions of non-contact AFM under ultra-high vacuum, the stacking height values can dramatically be overestimated due to variations in the tip-surface capacitive gradient, even though the KPFM controller nullifies the potential difference. We show that the number of atomic layers of a TMD can be safely assessed, only if the KPFM measurement is performed with a modulated bias amplitude reduced at its strict minimum or, even better, without any modulated bias. Last, the spectroscopic data reveal that defects at the TMD/oxide interface can have a counterintuitive impact on the electrostatic landscape, resulting in an apparent decrease of the measured stacking height by conventional nc-AFM/KPFM compared to non-defective sample areas. Hence, electrostatic free z-imaging proves to be a promising tool to assess the existence of defects in atomically thin TMD layers grown on oxides

cond-mat.mtrl-sci↗

arXiv2018

Strongly anisotropic spin relaxation in graphene/transition metal dichalcogenide heterostructures at room temperature

Graphene has emerged as the foremost material for future two-dimensional spintronics due to its tuneable electronic properties. In graphene, spin information can be transported over long distances and, in principle, be manipulated by using magnetic correlations or large spin-orbit coupling (SOC) induced by proximity effects. In particular, a dramatic SOC enhancement has been predicted when interfacing graphene with a semiconducting transition metal dechalcogenide, such as tungsten disulphide (WS$_2$). Signatures of such an enhancement have recently been reported but the nature of the spin relaxation in these systems remains unknown. Here, we unambiguously demonstrate anisotropic spin dynamics in bilayer heterostructures comprising graphene and WS$_2$. By using out-of-plane spin precession, we show that the spin lifetime is largest when the spins point out of the graphene plane. Moreover, we observe that the spin lifetime varies over one order of magnitude depending on the spin orientation, indicating that the strong spin-valley coupling in WS$_2$ is imprinted in the bilayer and felt by the propagating spins. These findings provide a rich platform to explore coupled spin-valley phenomena and offer novel spin manipulation strategies based on spin relaxation anisotropy in two-dimensional materials.

cond-mat.mes-hall↗