Tunable multiple nonvolatile resistance states in a MnSe-based van der Waals multiferroic tunnel junction

Two-dimensional (2D) van der Waals (vdW) multiferroic tunnel junctions (MFTJs) composed of a ferromagnetic metal and a ferroelectric barrier have controllable thickness and clean interface and can realize the coexistence of tunneling magnetoresistance (TMR) and tunneling electroresistance (TER). Therefore, they have enormous potential application in nonvolatile multistate memories. Here, using first principles combined with non-equilibrium Green's function method, we have systematically investigated the spin-dependent transport properties of Fe₃GeTe₂/MnSe/Fe₃GeTe₂ vdW MFTJs with various numbers of barrier layers. By controlling the polarization orientation of the ferroelectric barrier MnSe and the magnetization alignment of the ferromagnetic electrodes Fe₃GeTe₂, the MnSe-based MFTJs exhibit four nonvolatile resistance states, with the TMR (TER) becoming higher and reaching a maximum of 1.4 × 10⁶% (4114%) as the MnSe layers increase from a bilayer to a tetralayer. Using asymmetric Cu and Fe₃GeTe₂ as the electrodes, the TER can be further improved from 349% to 618%. Moreover, there is a perfect spin filtering effect in these MFTJs. This work demonstrates the potential applications of MnSe-based devices in multistate nonvolatile memories and spin filters, which will stimulate experimental studies on layer-controllable spintronic devices.