Negative-to-Positive Tunnel Magnetoresistance in van der Waals Fe3GeTe2/Cr2Ge2Te6/Fe3GeTe2 Junctions

The emergent van der Waals magnetic material is a promising component for spintronic devices with novel functionalities. Here, we report a transition of negative-to-positive magnetoresistance in Fe3GeTe2/Cr2Ge2Te6/Fe3GeTe2 van der Waals all-magnetic tunnel junctions with increasing the applied bias voltage. A negative magnetoresistance is observed first in Fe3GeTe2/Cr2Ge2Te6/Fe3GeTe2 tunnel junctions, where the resistance with antiparallel aligned magnetization of two Fe3GeTe2 electrodes is lower than that with parallel alignment, which is due to the opposite spin polarizations of two Fe3GeTe2 electrodes. With the bias voltage increasing, the spin polarization of the biased Fe3GeTe2 electrode is changed so that the spin orientations of two Fe3GeTe2 electrodes are the same. Our experimental observations are supported by the calculated spin-dependent density of states for Fe3GeTe2 electrodes under a finite bias. The significantly bias voltage-dependent spin transport properties in van der Waals magnetic tunnel junctions open a promising route for designing electrical controllable spintronic devices based on van der Waals magnets.