Optimize the electrical transport and low field magnetoresistance properties of La0.7Ca0.3MnO3@CoOx by CoO composite-cladding-grain boundary modification

Polycrystalline perovskite La0.7Ca0.3MnO3 (LCMO) has considerable magnetoresistance properties under high magnetic field holding, but it will lead to a decrease in magnetoresistance under low magnetic field, which will greatly limit its practical application. In order to improve the electrical transport and low field magnetoresistance (LFMR) properties of LCMO, a series of La0.7Ca0.3MnO3@CoOx (0 <= x <= 0.04) two-phase composite ceramics were prepared by sol-gel method based on the three-in-one strategy of CoO powder compositation-coating-grain boundary modification. The effects of CoO introduction on LCMO microstructure and LFMR were systematically analyzed. X-ray diffraction showed that the lattice parameters (a,b,c,v) of LCMO are inhibited, indicating an increase in the accumulation of CoO at the grain boundaries. Scanning electron microscopy showed that the grain boundaries were clear and the grains were closely connected, which proved the existence of the two-phase composite of LCMO and CoO. The resistivity-temperature curve showed the obvious metal-insulator transition, the CoO modified grain boundary increases the resistivity, the metal-insulator transition temperature moves to the low temperature region, and the increase in resistivity is explained by the small polaron model. Surprisingly: the CoO gradient recombination forms an insulator barrier, effectively inhibits the grain boundary connection, enhances the lattice and the grain boundary, and observed excellent LFMR performance of up to 78.48 %. The resulted show that CoO combination can effectively enhance the electrical transport and LFMR performance. This research expands the application prospect of LCMO materials in magnetic storage devices.