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

Abstract

Substitution of yttrium (Y³⁺) in La-Ca-Mn-O perovskites of the ABO₃ structure markedly affects the crystal structure and lattice constants as well as the resistivity (ρ), 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»T_c.