Half-Metallic Transport and Spin-Polarized Tunneling through the van der Waals Ferromagnet Fe₄GeTe₂

We examine the coherent spin-dependent transport properties of the van der Waals (vdW) ferromagnet Fe₄GeTe₂ using density functional theory combined with the nonequilibrium Green's function method. Our findings reveal that the conductance perpendicular to the layers is half-metallic, meaning that it is almost entirely spin-polarized. This property persists from the bulk to a single layer, even under significant bias voltages and with spin-orbit coupling. Additionally, using dynamical mean field theory for quantum transport, we demonstrate that electron correlations are important for magnetic properties but minimally impact the conductance, preserving almost perfect spin-polarization. Motivated by these results, we then study the tunnel magnetoresistance (TMR) in a magnetic tunnel junction consisting of two Fe₄GeTe₂ layers with the vdW gap acting as an insulating barrier. We predict a TMR ratio of ∼500%, which can be further enhanced by increasing the number of Fe₄GeTe₂ layers in the junction.