Transport and magnetic properties of nanosized La2/3(Ca0.6Ba0.4)1/3MnO3/xNiO composites

Two types of La2/3(Ca0.6Ba0.4)1/3MnO3/x NiO composites (x=0, 0.10, 0.20, 0.50 mol), named as Ax and Bx samples, were synthesized by different processes and sol-gel method. Magnetoresistance (MR) behaviors of Ax and Bx samples are found to be quite different. For example, as T<250 K, MR value of A0.1 sample is lager than that of B0.1 sample under H=7T. But in contrast, under H=0.5T, MR value of A0.1 sample is smaller than that of B0.1 sample. Moreover, MR maximum near Tc for Ax samples does almost not exist, while it for Bx samples does always. The experimental results have been explained by two-level model of tunneling MR and percolation model well.