A reversal of positive to negative magnetoresistance in Fe3O4-based heterostructures at room temperature by annealing

In this paper, a transition of magnetoresistance (MR) from positive to negative was obtained at room temperature by vacuum annealing of Fe3O4 (128 nm) / Si (with natural SiO2) heterostructures at 780 & DEG;C. Considering the wire-like nanograins with varying length and the effect of interface, the sign of MR is decided by the contribution of two Fe3O4 layers. One is the layer at the Fe3O4/SiO2 interface where the scattering of conducting electrons in the natural SiO2 layer on the top of Si can lead to spin polarization reversal of Fe3O4 and the other is the Fe3O4 far away from the absorbing interface. The reversal sign of MR indicates the dominant contrition of Fe3O4 far away from the absorbing interface as the stabilized SiO2 phase on top of the Si substrate with fewer ion defects by annealing the Fe3O4 film on natural Si at 780 & DEG;C. For the Fe3O4 film prepared on the substrate of corroded Si (chemically etching the natural SiO2 layer), positive MR is maintained even vacuum annealed at 780 & DEG;C, while for the Fe3O4 film on SiO2, an additional & alpha;-Fe2O3 phase is obtained even negative MR for films both as deposited and annealed at 780 & DEG;C. It can be concluded that the SiO2 layer on top of the substrate plays an important role in the interface and then the magnetotransport properties of the Fe3O4 heterostructures. Well property and negative spin polarization of Fe3O4 film can be obtained by vacuum annealing the Fe3O4 film on Si substrate with a proper thickness of natural SiO2 layer at 780 & DEG;C.& COPY; 2023 Elsevier B.V. All rights reserved.

Automated summary

Positive to negative transition of magnetoresistance (MR) at room temperature was achieved by vacuum annealing Fe3O4 (128 nm) / Si (with natural SiO2) heterostructures at 780°C. The sign of MR is determined by the contribution of two Fe3O4 layers, one at the Fe3O4/SiO2 interface and the other far away from the interface. The SiO2 layer on top of the substrate plays a crucial role in the magnetotransport properties of Fe3O4 heterostructures. Vacuum annealing the Fe3O4 film on Si substrate with a proper thickness of natural SiO2 layer at 780°C can lead to a well-property and negative spin polarization of Fe3O4 film.