Efficient spin filtering through Fe$_4$GeTe$_2$-based van der Waals heterostructures

Abstract: Utilizing ab initio simulations, we study the spin-dependent electronic transport characteristics within Fe$_4$GeTe$_2$-based van der Waals heterostructures. The electronic density of states for both free-standing and device-configured Fe$_4$GeTe$_2$ (F4GT) confirms its ferromagnetic metallic nature and reveals a weak interface interaction between F4GT and PtTe$_2$ electrodes, enabling efficient spin filtering. We observe a decrease in the magnetic anisotropy energy of F4GT in the device configuration, indicating reduced stability of magnetic moments and heightened sensitivity to external conditions. The transmission eigenstates of PtTe$_2$/ monolayer F4GT/PtTe$_2$ heterostructures demonstrate interference patterns affected by relative phases and localization, notably different in the spin-up and spin-down channels. The ballistic transport through a double-layer F4GT with a ferromagnetic configuration sandwiched between two PtTe$_2$ electrodes is predicted to exhibit an impressive spin polarization of 97$\%$ with spin-up electrons exhibiting higher transmission probability than spin-down electrons. Moreover, we investigate the spin transport properties of Fe$_4$GeTe$_2$/GaTe/Fe$_4$GeTe$_2$ van der Waals heterostructures sandwiched between PtTe$_2$ electrodes to explore their potential as magnetic tunnel junctions (MTJs) in spintronic devices. The inclusion of GaTe as a 2D semiconducting spacer between F4GT layers results in a tunnel magnetoresistance (TMR) of 487$\%$ at low bias and decreases with increasing bias voltage. In general, our findings underscore the potential of F4GT / GaTe / F4GT heterostructures to advance spintronic devices based on van der Waals materials.