From two- to multi-state vertical spin valves without spacer layer based on FeGeTe van der Waals homo-junctions.

Different than covalently bonded magnetic multilayer systems, high-quality interfaces without dangling bonds in van der Waals (vdW) junctions of two-dimensional (2D) layered magnetic materials offer opportunities to realize novel functionalities. Here, we report the fabrication of multi-state vertical spin valves without spacer layers by using vdW homo-junctions in which exfoliated FeGeTe nanoflakes act as ferromagnetic electrodes and/or interlayers. We demonstrate the typical behavior of two-state and three-state magnetoresistance for devices with two and three FeGeTe nanoflakes, respectively. Distinct from traditional spin valves with sandwich structures, our novel homo-junction-based spin-valve structure allows the straightforward realization of multi-state magnetic devices. Our work demonstrates the possibility of extend multi-state, non-volatile spin information to 2D magnetic homo-junctions, and it emphasizes the utility of vdW interface as a fundamental building block for spintronic devices.