Magnetic and electronic properties of transition-metal-substituted perovskite manganites-La0.7Ca0.3Mn0.95X0.05O3 (X=Fe,Co,Ni)

The magnetic and electronic properties of Fe-, Co-, Ni-substituted La0.7Ca0.3MnO3 were studied. Ferromagnetic-paramagnetic and metal-insulator transitions were significantly affected by Mn-site substitution although no observable differences were found in their crystal structures from x-ray diffraction analysis. Valence-band photoemission studies also showed that there were no appreciable changes in the electronic structures of each sample. Peak temperatures (T-p) at maximum resistivity decreased from 265 K of virgin LaCaMnO to 217, 203, and 171K for Ni-,Co-, and Fe-substituted LaCaMnO samples, respectively. As the T-p decreased, the electrical resistivity increased and the saturation magnetization decreased. The overall experimental results were well explained by considering superexchange interactions induced by substitution with magnetic ions having different magnetic moments. From our study, it is suggested that the magnetic properties of substituting elements should also be considered to deal with the physical properties of these LaCaMnXO systems. (C) 2001 American Institute of Physics.