Graphene-induced invertible magnetoresistance in variable phase iron oxides

Iron oxides are one of the oldest magnetic systems in history and have been studied extensively due to their phase-tunable magnetic and electronic properties. The combination of ferrimagnetic half-metallic magnetite (Fe₃O₄) with antiferromagnetic insulating hematite (α-Fe₂O₃) forms a so-called biphase iron oxide (BPIO) system that exhibits highly tunable magnetic and spin-transport properties in terms of phase and volume fraction. In this work, we report the interfacial physics between variations of these iron oxide phases with graphene (Gr) on magnetotransport in these heterostructures. Our experiments reveal that the inclusion of graphene in these heterostructures induces an inversion in the sign of magnetoresistance at finite temperatures. We explain this observation with an effective percolative transport model. Interestingly, the switching temperature and the sharpness of the transition can be further tuned by varying the phase volume fractions of the iron oxide layer and the crystallinity. The BPIO films, which grow naturally on Si substrates, exhibit the highest switching temperature. Our observations underscore the ability to induce magnetoresistive switching in abundant iron oxide grown on cost-effective, CMOS-compatible substrates by including a single layer of Gr, which has potential applications in modern devices and neuromorphic computing.