Spin-dependent transport in Fe 3 GaTe 2 and Fe n GeTe 2 ( n = 3–5) van der Waals ferromagnets for magnetic tunnel junctions

We present a first-principles investigation of the spin-dependent electronic structure and quantum transport properties of the van der Waals (vdW) ferromagnets Fe3GeTe2, Fe4GeTe2, Fe5GeTe2, and Fe3GaTe2, motivated by their growing use as electrodes in vdW magnetic tunnel junctions (MTJs). Using density functional theory combined with the non-equilibrium Green's function formalism within the linear-response regime, we analyze their Fermi surfaces, transmission coefficients, and orbital-resolved densities of states. Our results show that Fe3GeTe2, Fe4GeTe2, and Fe3GaTe2 exhibit a Fermi surface dominated by spin-up states, leading to nearly half-metallic out-of-plane conductance with spin polarizations exceeding 90% in the bulk. Among these compounds, Fe3GaTe2 stands out as the most robust case, with the Fermi energy lying deep within the spin-down transmission gap. For Fe5GeTe2, we compare the crystal structure adopted in previous theoretical studies with the recently reported experimental structure and show that the latter is expected to support a high spin polarization. We further investigate bilayer heterostructures as minimal MTJs, where the vdW gap acts as the tunneling barrier. The high spin polarization of the bulk materials is preserved in these bilayers, resulting in large tunneling magnetoresistance ratios on the order of several hundred percent. These findings underscore the promise of these materials, and in particular of Fe3GaTe2, for spintronics applications.