arXiv subjects

Sylvie Migot

Publications and source records attributed to Sylvie Migot.

8 recordsLinked to original sources

arXiv2026

Epitaxial $\mathrm{Co_2MnSi}$ with intrinsic magnetocrystalline anisotropy as a route to bias-field-free nonlinear half-metal magnonics at the nanoscale

Half-metallic Heusler compounds like $\mathrm{Co_2MnSi}$ allow to bridge magnonic and spintronic functionality for hybrid unconventional computing approaches with sought-after properties like 100% spin polarization and associated low Gilbert damping $α\leq 10^{-3}$. However, the desirable material parameters are inherently tied to the crystal lattice with a particularly critical dependence on structural order in $\mathrm{Co_2MnSi}$. To date, the successful fabrication of nanoscale devices with robust structural integrity remains yet a challenge, and consequently the impact of the material parameters on the resulting nonlinear spin-wave dynamics remains largely unexplored. Here, we report on a study of linear and nonlinear spin-wave dynamics in transversally magnetized $\mathrm{Co_2MnSi}$ waveguides with impeccable crystalline ordering. We show that epitaxial, $\mathrm{L2}_1$-ordered $\mathrm{Co_2MnSi}$ exhibits an intrinsic cubic anisotropy with first- and second-order contributions, stabilizing a magnetization alignment along the crystal $\langle110\rangle$ directions. We confirm the implication of an unaffected crystal structure resulting in preserved magnetic properties in the patterned structures. Herein, the persistent magnetocrystalline anisotropy reshapes the spin-wave dispersion which yields a first-order nonlinear instability suppression range extending over several GHz - even for vanishing bias fields. Moreover, the intrinsic magnetocrystalline anisotropy can be exploited to counteract shape demagnetization for a stabilized low bias field operation in the favourable Damon-Eshbach geometry with high group velocities and decay lengths. Together with the proven half-metallicity and ultralow Gilbert damping, this research establishes $\mathrm{Co_2MnSi}$ as a robust, scalable platform towards bias-field-free nonlinear half-metal magnonics.

cond-mat.mes-hall↗

arXiv2026

Grain boundary defects induced Tc increment in MnSi

The rapid advancement of digital technologies necessitates significant progress in functional materials, which are often derived from scarce elements and involve complex manufacturing processes. Additionally, the trend towards miniaturization in high-tech devices has heightened the demand for extremely small components with tailored functionalities. In the domains of ferromagnetic materials, the market is mostly dominated by rare-earth elements-based structures, which are also limited in abundance. In this work, we focus on the microstructure and properties of MnSi. It is a ferromagnetic material with a relatively low Curie temperature (TC) of 30 K. However, our study demonstrates that Tc can be increased by a factor of 4 through careful control of the crystal size. MnSi thin films were synthesized by combining two non-equilibrium techniques: magnetron sputtering and laser annealing. Laser annealing provoked the crystallinity evolution, by heat accumulation, of the barely crystallized films deposited by magnetron sputtering. The laser beam scanning parameters were adjusted to achieve different fluence values, pulse numbers, and pulse frequencies at each point of the film. Films with a crystal size of around 20 nm exhibited a TC of up to 120 K. These properties were obtained under conditions of low fluence and a high number pulse. Local laser impacts were applied to as-deposited samples, enabling spatially controlled crystallization. The interface between the poorly and well-crystallized regions was showcased using high-resolution transmission electron microscopy (HR-TEM). A spatial resolution of approximately 100 μm was achieved. These results demonstrate the strong potential of laser annealing as a versatile and promising approach for the fabrication of miniaturized devices.

cond-mat.mtrl-sci↗

arXiv2023

Room Temperature Spin to Charge Conversion in Amorphous Topological Insulating Gd-Alloyed BixSe1-x/CoFeB Bilayers

Disordered topological insulator (TI) films have gained intense interest by benefiting from both the TIs exotic transport properties and the advantage of mass production by sputtering. Here, we report on the clear evidence of spin-charge conversion (SCC) in amorphous Gd-alloyed BixSe1-x (BSG)/CoFeB bilayers fabricated by sputtering, which could be related to the amorphous TI surface states. Two methods have been employed to study SCC in BSG/CoFeB(5 nm) bilayers with different BSG thicknesses. Firstly, spin pumping is used to generate a spin current in CoFeB and to detect SCC by inverse Edelstein effect. The maximum SCC efficiency (SCE) is measured as large as 0.035 nm in a 6 nm thick BSG sample, which shows a strong decay when tBSG increases due to the increase of BSG surface roughness. The second method is the THz time-domain spectroscopy, which reveals a small tBSG dependence of SCE, validating the occurrence of a pure interface state related SCC. Furthermore, our angle-resolved photoemission spectroscopy data show dispersive two-dimensional surface states that cross the bulk gap until to the Fermi level, strengthening the possibility of SCC due to the amorphous TI states. Our studies provide a new experimental direction towards the search for topological systems in the amorphous solids.

cond-mat.mtrl-sci↗

arXiv2022

One-Step Formation of Plasmonic Cu Nanodomains in p-Type Cu$_2$O Matrix Films for Enhanced Photoconversion of n-ZnO/p-Cu$_2$O Heterojunctions

Plasmonic Cu nanoparticles were in-situ grown into a Cu$_2$O semiconductor matrix by using reactive magnetron sputtering and adjusting the amount of oxygen available during the synthesis in order to prevent the oxidation of part of copper atoms landed on the film surface. Varying only the oxygen flowrate (OFR) and using a single Cu target it was possible to observe the evolution in the simultaneous formation of metallic Cu and Cu$_2$O phases for oxygen-poor conditions. Suchformation is accompanied by the development of the surface plasmon band (SPB) corresponding to Cu, as evidenced by UV-Vis spectrophotometry and spectroscopic ellipsometry. The bandgap values of the elaborated composites containing embedded Cu plasmonic nanodomains were lower than the bandgap of single-phased Cu$_2$O films, likely due to the higher defect density associated to the nanocrystalline nature of films, promoted by the presence of metallic Cu. The resistivity of the thin films increased with more oxidative deposition conditions and was associated to an increase in Cu$_2$O/Cu ratio and smaller and more isolated Cu particles, as evidenced by high resolution transmission electron microscopy and X-ray diffraction. Photoconversion devices based on the studied nanocomposites were characterized by I-V and spectral photocurrent measurements, showing an increase in the photocurrent density under light illumination as consequence of the plasmonic particles excitation leading to hot carrier's injection in the nearby ZnO and Cu$_2$O semiconductors.

physics.app-ph↗

arXiv2022

Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques

Spintronics is showing promising results in the search for new materials and effects to reduce energy consumption in information technology. Among these materials, ferrimagnets are of special interest, since they can produce large spin currents that trigger the magnetization dynamics of adjacent layers or even their own magnetization. Here, we present a study of the generation of spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice magnetization is dominant at room temperature. Magnetic properties such as the saturation magnetization are deduced from magnetometry measurements while damping constant is estimated from spin-torque ferromagnetic resonance (ST-FMR). We show that the overall damping-like (DL) and field-like (FL) effective fields as well as the associated spin Hall angles can be reliably obtained by performing the dependence of ST-FMR by an added dc current. The sum of the spin Hall angles for both the spin Hall effect (SHE) and the spin anomalous Hall effect (SAHE) symmetries are: $θ_{DL}^{SAHE} + θ_{DL}^{SHE}=-0.15 \pm 0.05$ and $θ_{FL}^{SAHE} + θ_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find that $θ_{DL}^{SHE}$ is positive and dominated by the negative $θ_{DL}^{SAHE}$. The present study paves the way for tuning the different symmetries in spin conversion in highly efficient ferrimagnetic systems.

cond-mat.mes-hall↗

arXiv2021

Large perpendicular magnetic anisotropy in Ta/CoFeB/MgO on full coverage monolayer MoS2 and first principle study of its electronic structure

Perpendicularly magnetized spin injector with high Curie temperature is a prerequisite for developing spin optoelectronic devices on 2D materials working at room temperature (RT) with zero applied magnetic field. Here, we report the growth of Ta/CoFeB/MgO structures with a large perpendicular magnetic anisotropy (PMA) on full coverage monolayer (ML) MoS2. A large perpendicular interface anisotropy energy of 0.975mJ/m2 has been obtained at the CoFeB/MgO interface, comparable to that observed in magnetic tunnel junction systems. It is found that the insertion of MgO between the ferromagnetic metal (FM) and the 2D material can effectively prevent the diffusion of the FM atoms into the 2D material. Moreover, the MoS2 ML favors a MgO(001) texture and plays a critical role to establish the large PMA. First principle calculations on a similar Fe/MgO/MoS2 structure reveal that the MgO thickness can modify the MoS2 band structure, from an indirect bandgap with 7ML-MgO to a direct bandgap with 3ML-MgO. Proximity effect induced by Fe results in a splitting of 10meV in the valence band at the Γ point for the 3ML-MgO structure while it is negligible for the 7ML-MgO structure. These results pave the way to develop RT spin optoelectronic devices on 2D transition-metal dichalcogenide materials.

cond-mat.mtrl-sci↗

arXiv2020

Current-induced spin torques on single GdFeCo magnetic layers

Spintronics exploits spin-orbit coupling (SOC) to generate spin currents, spin torques, and, in the absence of inversion symmetry, Rashba, and Dzyaloshinskii-Moriya interactions (DMI). The widely used magnetic materials, based on 3d metals such as Fe and Co, possess a small SOC. To circumvent this shortcoming, the common practice has been to utilize the large SOC of nonmagnetic layers of 5d heavy metals (HMs), such as Pt, to generate spin currents by Spin Hall Effect (SHE) and, in turn, exert spin torques on the magnetic layers. Here, we introduce a new class of material architectures, excluding nonmagnetic 5d HMs, for high-performance spintronics operations. We demonstrate very strong current-induced torques exerted on single GdFeCo layers due to the combination of large SOC of the Gd 5d states, and inversion symmetry breaking mainly engineered by interfaces. These "self-torques" are enhanced around the magnetization compensation temperature (close to room temperature) and can be tuned by adjusting the spin absorption outside the GdFeCo layer. In other measurements, we determine the very large emission of spin current from GdFeCo. This material platform opens new perspectives to exert "self-torques" on single magnetic layers as well as to generate spin currents from a magnetic layer.

cond-mat.mes-hall↗

arXiv2020

Temperature dependence of transport mechanisms in organic multiferroic tunnel junctions

Organic multiferroic tunnel junctions (OMFTJs) with multi-resistance states have been proposed and drawn intensive interests due to their potential applications, for examples of memristor and spintronics based synapse devices. The ferroelectric control of spin-polarization at ferromagnet (FM)/ferroelectric organic (FE-Org) interface by electrically switching the ferroelectric polarization of the FE-Org has been recently realized. However, there is still a lack of understanding of the transport properties in OMFTJs, especially the interplay between the ferroelectric domain structure in the organic barrier and the spin-polarized electron tunneling through the barrier. Here, we report on a systematic study of the temperature dependent transport behavior in La0.6Sr0.4MnO3/PVDF/Co OMFTJs. It is found that the thermal fluctuation of the ferroelectric domains plays an important role on the transport properties. When T>120K, the opposite temperature dependence of resistance for in up and down ferroelectric polarization states results in a rapid diminishing of tunneling electroresistance (TER). These results contribute to the understanding of the transport properties for designing high performance OMFTJs for memristor and spintronics applications.

cond-mat.mtrl-sci↗