Tunable long-range spin transport in a van der Waals Fe₃GeTe₂/WSe₂/Fe₃GeTe₂ spin valve

The seamless integration of two-dimensional (2D) ferromagnetic materials with similar or dissimilar materials can widen the scope of low-power spintronics. In this regard, a vertical van der Waals (vdW) heterostructure of 2D ferromagnets with semiconducting transition metal dichalcogenides (TMDCs) forms magnetic junctions with exceptional stability and electrical control. Interestingly, 2D metallic Fe₃GeTe₂ (FGT) reveals above room temperature Curie temperatures and has large magneto anisotropy due to spin-orbit coupling. In addition, it also possesses topological states and a large Berry curvature. Herein, we designed the FGT/WSe₂/FGT vdW heterostructure with a uniform and sharp interface so that FGT could maintain its inherent electronic properties. Also, the uniform thickness of the barrier provides a smooth flow of spins through the junctions as tunneling exponentially decays with an increasing barrier thickness. However, strong energy-dependent spin polarization is crucial for achieving optimum spin valve properties, such as large tunneling magnetoresistance (TMR) along with the manipulation of the magnitude and sign reversal. We have observed a shifting of high-energy localized minority spin states toward low-energy regions, which causes spin polarization fluctuation between -42.5% and 41% over a wide range of bias voltage. This leads to a negative TMR% of ∼-100% at 0.1 V Å^-1 and also a large positive TMR% at 0.2 V Å^-1 and -0.4 V Å^-1. Besides, the system exhibits a highly tunable large anomalous Hall conductivity (AHC) of 626 S cm^-1. Interestingly, such unprecedented electronic behaviour with large and switchable spin polarization, anomalous Hall conductivity and TMR can be incorporated into MTJ devices, which provide electrical control and long-range spin transport. Additionally, the system emerges as a standout candidate in low-power spintronic devices (e.g., MRAM and magnetic sensors) owing to its distinctive energy-dependent electronic structure with a wide range of external bias.