Electrical and low-field magnetoresistance transport effect of La_0.7Ca_0.3MnO₃: MnO₂ composite ceramics

Simultaneously increasing the temperature coefficient of resistivity (TCR) and low-field magnetoresistance (LFMR) has become important. Generally, Mn ions play an important role in the change of electromagnetic properties of the system, and the change of Mn³⁺/Mn⁴⁺ causes the J-T effect and DE interaction. In this paper, (La_0.7Ca_0.3MnO₃)_1-x: (MnO₂)_x(x = 0–0.2) ceramics are prepared by sol-gel and solid-state routine. The morphology, structure, and transport properties are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS), and four-probe technique test methods. The XRD results show that all samples have high crystallinity and density, and the structure (space group) are determined to be Pnma. The SEM grain statistics diagram results show that with the increase of MnO₂, the grain size increases and grain boundary decreases. The XPS shows that Mn⁴⁺ ions content increases first and then decreases. Moreover, the electrical and magnetic transport properties of the samples are improved, resistivity(ρ), TCR increased from 39.89 to 44.29%·K⁻¹, MR increased from 53.29 to 75.42%, which is larger than most of the other reported values and provides a new direction for the selection of infrared detection materials.