The influence of the composition of Fe2O3 on TCR and MR properties of La0.67Ca0.33MnO3@xFe2O3 ceramics based on the sol-gel method

This study focuses on the improvement of magnetoresistance (MR) in a two-phase composite systems. The spin-polarization tunneling caused by the introduction of metal oxides (Fe 2 O 3 ) coating grains is a key link to enhance magnetoresistance performance. Two-phase composite ceramics La 0.67 Ca 0.33 MnO 3 @ x Fe 2 O 3 (LCMOF) (0 ≤ x  ≤ 0.009) were prepared by sol-gel method, and the microstructure, electrical transport and magnetoresistance (MR) properties under the composite system were systematically studied. The XRD results indicate that the recombination of the second phase causes subtle structural distortion but still presents an orthogonal perovskite structure. The surface SEM results show that the grain boundaries of the material are clear, and the grain connections are tight. The coexistence of LCMOF and MnO phases exists in the sectional SEM images, which proves the occurrence of ion substitution. The ρ - T curve shows a drastic metal-insulator transition. The continuous recombination of Fe 2 O 3 increases the resistivity, which can be explained by the grain boundary effect and the dual-channel model. A noteworthy phenomenon was observed, when x  = 0.009, the optimized MR was significantly enhanced to 72.94 %, and the sample performance was significantly improved, which was attributed to the spin-polarization tunneling effect. This study expands the application prospects of LCMOF composite phases in fields such as magnetic sensors, magnetic storage, and thermistors.