In this paper we show the effect of Mn site substitution $(<~10\%)$ by Co and Cr on the magnetotransport properties of ceramic samples of ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_3.$ Resistivity, magnetization, and magnetoresistance were systematically investigated as a function of doping. An increase in resistivity and a diminution of metal-insulator transition and Curie temperatures was observed as a consequence of both Co and Cr doping. The evolution of the number of neighbors ferromagnetically coupled to Mn was studied in each sample, and the results suggest some degree of ferromagnetic coupling between ${\mathrm{Cr}}^{3+}$ and Mn ions. Implications of both ferromagnetic Cr ${}^{3+}-\mathrm{O}-{\mathrm{Mn}}^{3+}$ superexchange and double exchange interactions are discussed. We also found the existence of an optimum doping level that enhances colossal magnetoresistance. This has been explained considering electron localization due to magnetic disorder induced by doping in the Mn site.

• Received 29 February 2000

DOI:https://doi.org/10.1103/PhysRevB.62.5678