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.