arXiv subjects

C. Guillemard

Publications and source records attributed to C. Guillemard.

3 recordsLinked to original sources

arXiv2023

Large-area synthesis of ferromagnetic Fe$_{5-x}$GeTe$_{2}$/graphene van der Waals heterostructures with Curie temperature above room temperature

Van der Waals (vdW) heterostructures combining layered ferromagnets and other two-dimensional (2D) crystals are promising building blocks for the realization of ultra-compact devices with integrated magnetic, electronic and optical functionalities. Their implementation in various technologies depends strongly on the development of a bottom-up scalable synthesis approach allowing to realize highly uniform heterostructures with well-defined interfaces between different 2D layered materials. It also requires that each material component of the heterostructure remains functional, which ideally includes ferromagnetic order above room temperature for 2D ferromagnets. Here, we demonstrate large-area growth of Fe$_{5-x}$GeTe$_{2}$/graphene heterostructures achieved by vdW epitaxy of Fe$_{5-x}$GeTe$_{2}$ on epitaxial graphene. Structural characterization confirmed the realization of a continuous vdW heterostructure film with a sharp interface between Fe$_{5-x}$GeTe$_{2}$ and graphene. Magnetic and transport studies revealed that the ferromagnetic order persists well above 300 K with a perpendicular magnetic anisotropy. In addition, epitaxial graphene on SiC(0001) continues to exhibit a high electronic quality. These results represent an important advance beyond non-scalable flake exfoliation and stacking methods, thus marking a crucial step toward the implementation of ferromagnetic 2D materials in practical applications.

cond-mat.mtrl-sci↗

arXiv2020

Engineering Co$_2$MnAl$_x$Si$_{1-x}$ Heusler compounds as a model system to correlate spin polarization, intrinsic Gilbert damping and ultrafast demagnetization

Engineering of magnetic materials for developing better spintronic applications relies on the control of two key parameters: the spin polarization and the Gilbert damping responsible for the spin angular momentum dissipation. Both of them are expected to affect the ultrafast magnetization dynamics occurring on the femtosecond time scale. Here, we use engineered Co2MnAlxSi1-x Heusler compounds to adjust the degree of spin polarization P from 60 to 100% and investigate how it correlates with the damping. We demonstrate experimentally that the damping decreases when increasing the spin polarization from 1.1 10-3 for Co2MnAl with 63% spin polarization to an ultra-low value of 4.10-4 for the half-metal magnet Co2MnSi. This allows us investigating the relation between these two parameters and the ultrafast demagnetization time characterizing the loss of magnetization occurring after femtosecond laser pulse excitation. The demagnetization time is observed to be inversely proportional to 1-P and as a consequence to the magnetic damping, which can be attributed to the similarity of the spin angular momentum dissipation processes responsible for these two effects. Altogether, our high quality Heusler compounds allow controlling the band structure and therefore the channel for spin angular momentum dissipation.

cond-mat.mtrl-sci↗

arXiv2018

Charge-spin current conversion in high quality epitaxial Fe/Pt systems: isotropic spin Hall angle along different in-plane crystalline directions

We report the growth of MgO[001]//Fe(6 nm)/MgO(7 nm) and MgO[001]//Fe(6 nm)/Pt(6 nm) by molecular beam epitaxy and show that the full characterization by spin-orbit ferromagnetic resonance (SO-FMR) allows the determination of magnetic anisotropies as by classical FMR-only studies. The spin mixing conductance of epitaxial Fe/Pt interface was measured to be (1.5 +- 0.5)x10^19 m^2, and the effective spin Hall angle (SHA), was estimated at different in-plane crystalline directions. It was found that SHA is the same in all directions. When taking into account high enough excitation frequencies to achieve uniform precession of magnetization, the effective spin hall angle for epitaxial Pt in Fe/Pt is 0.051 +- 0.005. We address about the proper conditions to determine those relevant spintronics parameters.

cond-mat.mtrl-sci↗