The Fabrication And Properties Studies In La-Ca-Mn-O Colossal Magnetoresistance Materials

Colossal magnetoresistance material is formed by partially doping with divalent alkali metal like Ca, Sr and Ba into 3d transitional metal manganese oxide RE-Mn-O(RE, trivalent rare earth metal, like La, Pr, Sm, Nb and Gd). The doping leads to great change of magnetoresistance which brings CMR effect. This effect was used in magnetic recording at first. Then extensive studies have been conduced on these materials, including laser induced thermoelectric voltage effect in laser power meter and the gigantic resistance variation during metal-insulator transitions which will be used in bolometer.La_1-xCa_xMnO₃ polycrystalline has been prepared by conventional Solid-State reaction method. With the best reaction condition, the system with different Ca component(x=0.15,0.25,0.30,0.33,0.35,0.37,0.40,0.45,0.50) were investigated. And we doped silver 2-15wt% into La_0.67Ca_0.33MnO₃ in order to modify its magnetic and transport properties. The laser irradiation process employed a continuous CO₂ laser as the main heat source to irradiate La_0.67Ca_0.33MnO₃. Structure and electric transportation performance of this kind of material is investigated by means of X-ray Diffraction (XRD), Scattering Electronic Microscope (SEM), Raman Scattering, X-ray Photo Electron Spectroscopy (XPS), Resistance–Temperature (R-T) and Magnetoresistance-Temperature (MR-T) curve measurement.The best reaction condition is 10h calcining at 1000℃and 12h sintering at 1050℃. The results shows that the sample with x=0.33 possesses the best insulator-mental transition temperature. And the resistance of La_1-xCa_xMnO₃ decreaseed first with the icreasing of x which is from 0.15 to 0.33, and then increased when x increasing from 0.33 to 0.50. And it is found that the double-peak appeared in the R-T curve of La_0.67Ca_0.33MnO₃. This property is explained on the basis of the phase separation caused by the distribution of eg electrons. The resistance of Ag-doped La_0.67Ca_0.33MnO₃ kept decreasing with the increasing of Ag from 2wt%-15wt%. And the insulator-mental temperature of 4wt%Ag is the highest which is higher by 20K...