Transport and magnetic properties in La0.7Ca0.3Mn1−xCuxO3

The resistivity, ac susceptibility, electron spin resonance (ESR), and X-ray photoemission spectroscopy (XPS) were investigated in La0.7Ca0.3Mn1−xCuxO3 (x=0, 0.1, and 0.15). It was found that the resistivity becomes larger and the paramagnetic to ferromagnetic transition temperature TC shifts to lower temperatures with increasing Cu-doping level. However, the insulator–metal and magnetic transition temperatures of the system are still high even when the content of Cu is equal to 0.15, which is also confirmed by the characterizations of magnetization and resistivity of La0.7Ca0.3Mn0.85Cu0.15O3 epitaxial film. Our analysis shows that the main effect arises from the proportion variation of Mn4+ ions. Taking Cu 2p3/2 core level spectra into consideration, we pointed out that there are both Cu3+ and Cu2+ ions in the system.