Effect of Mn-site doping on the magnetotransport properties of the colossal magnetoresistance compound La(2/3)Ca(1/3)Mn(1-x)A(x)O(3) (A = Co,Cr; x <=0.1)

In this paper we show the effect of Mn site substitution (less than or equa l to 10%) by Co and Cr on the magnetotransport properties of ceramic sample s of La2/3Ca1/3MnO3. Resistivity, magnetization, and magnetoresistance were systematically investigated as a function of doping. An increase in resist ivity and a diminution of metal-insulator transition and Curie temperatures was observed as a consequence of both Ca and Cr doping. The evolution of t he number of neighbors ferromagnetically coupled to Mn was studied in each sample, and the results suggest some degree of ferromagnetic coupling betwe en Cr3+ and Mn ions. Implications of both ferromagnetic Cr3+-O-Mn3+ superex change and double exchange interactions are discussed. We also found the ex istence 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.