Effect of Y substitution in La-Ca-Mn-O perovskites showing giant magnetoresistance

Substitution of yttrium (Y3+) in La-Ca-Mn-O perovskites of the ABO(3) structure markedly affects the crystal structure and lattice constants as well as the resistivity (rho), ferromagnetic transition temperature (T-c), and the temperature corresponding to the insulator-metal-like transition (T-p). The two important parameters which control the electronic transport and the magnetic behavior are the Mn4+ content and the effective radius of the A-site cation. The substitution by Y, which changes the A-site radius, is compared to pressure effect. For certain Y concentrations we observe substantial enhancement of the negative magnetoresistance at temperatures T<T-c and a large positive magnetoresistance at T much greater than T-c.