Electrical and Magnetotransport Properties of ${rm La}_{{0.7}}{rm Ca}_{{0.3}}{rm Mn}_{{1-x}}{rm Co}_{{x}}{rm O}_{3}$

摘要

This paper presents a detailed study on the Co-doping influence on the electrical and magnetotransport properties of ${rm La}_{0.7}{rm Ca}_{0.3}{rm Mn}_{1-x}{rm Co}_{x}{rm O}_{3}(x={0.09}{-}0.17)$ prepared by solid-state reaction. Magnetic measurements versus temperature revealed a gradual decrease of the magnetization $(M)$ and Curie temperature $(T_{C})$ with increasing Co concentration $(x)$ . The $T_{C}$ values vary from 194 to 159 K as changing $x$ from 0.09 to 0.17, respectively. $H/M$ versus $M^{2}$ performances around $T_{C}$ prove the $x={0.09}$ sample undergoing a first-order magnetic phase transition (FOMT) while the samples with $xgeq 0.11$ undergo a second-order magnetic phase transition (SOMT). The other with $x={0.10}$ is considered as a threshold concentration of the FOMT–SOMT transformation. Considering temperature dependences of resistivity, $rho(T)$ , in the presence and absence of the magnetic field, the samples (excepting for $x={rm 0.17}$ ) exhibit a metal- –insulator transition at $T_{P}=60{-}160~{rm K}$ , which shifts toward lower temperatures with increasing $x$ . In the metallic-ferromagnetic region, the $rho(T)$ data are well fitted to a power function $rho(T)=rho_{0}+rho_{2}T^{2}+rho_{4.5}T^{4.5}$ . This indicates electron–electron and electron–magnon scattering processes are dominant at temperatures $Ttheta_{D}/2$ ( $theta_{D}$ is the Debye temperature) and $T_{P}