Speaker
Description
Recent advances in van der Waals (vdW) ferromagnets have opened innovative avenues for spintronic device design. In this work, we present a comprehensive theoretical investigation of coherent spin-dependent transport in the FGT family of vdW ferromagnets. Using density functional theory combined with the non-equilibrium Green's function method, we demonstrate that charge transport perpendicular to the layers exhibits robust half-metallicity driven by its intrinsic electronic structure [1]. Remarkably, this behavior persists from the bulk down to a single layer, remaining resilient under significant bias voltages and in the presence of spin-orbit coupling. We further analyze the tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions composed of various FGT combinations, where the vdW gap serves as the insulating barrier. Notably, a maximum TMR ratio of 800% is achieved in an Fe$_3$GaTe$_2$ bilayer system, and is further enhanced by incorporating additional layers.
Expanding our study to include dynamical effects via an extended dynamical mean field theory approach [2], we examine the influence of electronic correlations in Fe$_4$GeTe$_2$. While transport remains largely coherent at low bias, above ~0.5 V, spin-down Fe $3d$ states enter the bias window, triggering inelastic scattering and destroying coherence. This results in broadened spectral features and enhanced density of states near the Fermi level. A current decomposition confirms a growing incoherent contribution beyond this threshold.
References
[1] A. Halder, D. Nell, A. Sihi, A. Bajaj, S. Sanvito, and A. Droghetti, Half-Metallic Transport and Spin-Polarized Tunneling through the van der Waals Ferromagnet Fe4GeTe2, Nano Lett. 24, 9221 (2024).
[2] D. Nell, S. Sanvito, I. Rungger, and A. Droghetti, Effect of dynamical electron correlations on the tunnelling magnetoresistance of Fe/MgO/Fe(001) junctions, Phys. Rev. B 111, (2025).
