Tailorable multiferroic tunnel junctions from all-van der Waals multilayer stacking.

Multiferroic tunnel junctions (MFTJs) represent a class of multistate, non-volatile spintronic devices, in which electron tunnelling can be manipulated by switching long-range lattice and spin orders. In contrast to conventional oxide-based MFTJs, MFTJs constructed from two-dimensional van der Waals (vdW) crystals promise minimal defect concentration in the constituents and at interfaces, which may allow for probing intrinsic tunnelling physics and the development of high-performance devices. Here we construct Fe3GeTe2/CuInP2S6/Fe3GeTe2 all-vdW MFTJs by assembling multilayer flakes of ferromagnetic Fe3GeTe2 electrodes and a ferroelectric CuInP2S6 spacer. These MFTJs exhibit four non-volatile resistance states featuring sizable tunnelling magnetoresistance of ∼102% and tunnelling electroresistance of ∼104%. To tune the properties of the vdW MFTJ, we make use of the flexibility in material choice offered by vdW heterostructure devices; we use Fe3GeTe2/Fe5GeTe2 asymmetric electrodes to boost the tunnelling electroresistance by 103%, we integrate In2Se3 as a ferroelectric with a smaller bandgap to enhance the ON-state current density by 104% to 104 A cm-2 and we use Fe3GaTe2 electrodes to demonstrate room temperature operation. Furthermore, when we combine the asymmetric ferromagnetic electrodes with the small-bandgap ferroelectric spacer to construct Fe3GeTe2/In2Se3/Fe5GeTe2 MFTJs, we simultaneously realized tunnelling electroresistance of 106% and an ON-state current density of 104 A cm-2, both two orders of magnitude higher than the highest values achieved with conventional oxide-based MFTJs. In the future, our all-vdW MFTJs with the tailorability of all functional layers may make it possible to investigate fundamental aspects of interlayer tunnelling and enable the design of functional magnetoelectric nanodevices.