Spin current has different symmetries. In 5d transition metals with a cubic structure, we find the orthogonal or “conventional” spin Hall effect (SHE) symmetry as in Pt, Ta, and W [1]. Here, when a charge current Jc is injected along x, the transverse spin current Js generated along z transports electrons with y spin polarization [1]. In magnetic materials, Js might transport electrons with spin polarization parallel to their magnetization. However, if they have strong spin-orbit coupling, Js with the orthogonal SHE symmetry also survives. We have shown that for GdFeCo [2].

In the first part of my talk, I will present results on a new heterostructure combining 2D materials such as graphene (Gr) and 3D materials such as Fe and Pt. Through spin pumping ferromagnetic resonance, we show a record efficiency for charge current production at room temperature in Fe/Gr/Pt. The gain is 34 times over Fe/Pt. The charge current production is anisotropic, following the hexagonal symmetry of Gr. The experimental results are supported by first-principles calculations [3].

In the second part, I will present results with the van der Waals topological semimetal  NbIrTe₄, which has an orthorhombic crystallographic structure and a missing reflection plane. This allows the production of spin current along z with spin polarization also along z. The bulk topological Weyl semimetal nature of NbIrTe₄, characterized by its Weyl cone, significantly enhances the out-of-plane (OOP) spin Berry curvature, enabling an unprecedented OOP spin Hall conductivity exceeding 10⁵ ℏ/2e⋅Ω^-1m^-1. This enhancement enables efficient and field-free spin-orbit torque switching of perpendicular magnetization with a low current density of 1.4 MA/cm². The improved spin Hall conductivity reduces the overall power consumption by more than two orders of magnitude compared to existing systems, such as heavy metals [4].

Thanks to H2020-RISE ULTIMATE-I (ID 101007825), ERC CoG MAGNETALLIEN (ID 101086807) projects for financial support and to all collaborators [1-5].

References:

[1]          J.-C. Rojas-Sánchez and A. Fert, Phys Rev. Applied 11, 054049 (2019)
[2]          D. Céspedes-Berrocal, et al. Advanced Materials 33, 2007047 (2021)
[3]          A. Anadón, et al. Adv. Materials 37, 241854 (2025)
[4]          W. Yang, et al. https://arxiv.org/abs/2504.05280