arXiv subjects

V. T. Pham

Publications and source records attributed to V. T. Pham.

5 recordsLinked to original sources

arXiv2023

Electrical measurement of the Spin Hall Effect isotropy in a ferromagnet

The spin-dependent transport properties of paramagnetic metals are roughly invariant under rotation. By contrast, in ferromagnetic materials the magnetization breaks the rotational symmetry, and thus the spin Hall effect is expected to become anisotropic. Here, using a specific design of lateral spin valves, we measure electrically the spin Hall Effect anisotropy in NiCu and NiPd, both in their ferromagnetic and paramagnetic phases. We show that the appearance of the ferromagnetic order does not lead to a sizeable anisotropy of the spin charge interconversion in these materials.

cond-mat.mtrl-sci↗

arXiv2019

Spin dependent transport characterization in metallic lateral spin valves using 1D and 3D modeling

We present the analysis of the spin signals obtained in NiFe based metallic lateral spin valves. We exploit the spin dependent diffusive equations in both the conventional 1D analytic modeling as well as in 3D Finite Element Method simulations. Both approaches are used for extracting the spin diffusion length $l_{sf}^{N}$ and the effective spin polarization $P_{eff}$ in Py/Al, Py/Cu and Py/Au based lateral nano-structures at both $300\,K$ and $77\,K$. Both the analytic modeling and 3D Finite Element Method simulations give consistent results. Combination of both models provides a powerful tool for reliable spin transport characterization in all metallic spin valves and gives an insight into the spin/charge current and spin accumulations 3D distributions in these devices. We provide the necessary ingredients to develop the 3D finite element modeling of diffusive spin transport.

cond-mat.mtrl-sci↗

arXiv2018

Cross-shaped nanostructures for the study of spin to charge interconversions using spin-orbit coupling in non-magnetic materials

Several spin-orbit effects allow performing spin to charge inter-conversion: the spin Hall effects, the Rashba effect, or the spin-momentum locking in topological insulators. Here we focus on how the detection of this inter-conversion can be made electrically, using three different cross-shaped nanostructures. We apply these measurement configurations to the case of the spin Hall effect in Pt, using CoFe electrodes to detect and inject spins. Both the direct and inverse spin Hall effect can be detected, with a spin Hall signal up to two order of magnitude higher than that of nonlocal measurements in metallic lateral spin valves, and with a much simpler fabrication protocol. We compare the respective signal amplitude of the three proposed geometries. Finally, comparison of the observed spin signals with finite element method calculations allows extracting the spin Hall angle and the spin diffusion length of Pt.

cond-mat.mtrl-sci↗

arXiv2017

Large enhancement of the spin Hall effect in Au by scattering with side-jump on Ta impurities

We present measurements of the Spin Hall Effect (SHE) in AuW and AuTa alloys for a large range of W or Ta concentrations by combining experiments on lateral spin valves and Ferromagnetic-Resonance/spin pumping technique. The main result is the identification of a large enhancement of the Spin Hall Angle (SHA) by the side-jump mechanism on Ta impurities, with a SHA as high as + 0.5 (i.e $50\%$) for about 10\% of Ta. In contrast the SHA in AuW does not exceed + 0.15 and can be explained by intrinsic SHE of the alloy without significant extrinsic contribution from skew or side-jump scattering by W impurities. The AuTa alloys, as they combine a very large SHA with a moderate resistivity (smaller than $85\,μΩ.cm$), are promising for spintronic devices exploiting the SHE.

cond-mat.mtrl-sci↗

arXiv2012

Fixed point forms of the parallel symmetric sandpile model

This paper presents a generalization of the sandpile model, called the parallel symmetric sandpile model, which inherits the rules of the symmetric sandpile model and implements them in parallel. In this new model, at each step the collapsing of the collapsible columns happens at the same time and one collapsible column is able to collapse on the left or on the right but not both. We prove that the set of forms of fixed points of the symmetric sandpile model is the same as the one of that model using parallel update scheme by constructing explicitly the way (in the parallel update scheme) to reach the form of an arbitrary fixed point of the sequential model.

cs.DM↗