We report a low field (H=0.5 T) magnetoresistance of colossal magnetoresistive (CMR) composites prepared with ferromagnetic (FM)-antiferromagnetic (AFM) coupled system (100-x) La0.7 Pb0.3 Mn O3 (LPMO) +x Pr0.63 Ca0.37 Mn O3 with x=0-85 wt %. A large increase (∼16% maximum) of magnetoresistance (MR) (∼10% for pure LPMO) is observed at a relatively higher optimum concentration (x=70% AFM). Interesting double peaks are observed for lower AFM concentrations (x≤35%) in the resistivity-temperature [ρ (T)] curve: one due to the usual intrinsic double exchange interaction (between Mn3+ and Mn4+) mechanism and the other due to the stronger FM-AFM coupling for lower concentration. Unlike the usual ceramic CMR material, thermoelectric power (TEP) in this system is also nonadditive in character, indicating the presence of additional defects and strain in this composites. A two-channel (conducting and semiconductor) model has been used which fit well with the ρ (T) data near the optimum concentration x=70%. Around this highest AFM concentration, showing maximum MR, the corresponding TEP is also higher than those of the individual parent compound, which indicates the presence of maximum grain boundary effect and defects. Positron annihilation lifetime data of the composites also support the presence of such defects and strain in the system with maximum around the critical concentration xC =70%.
All Science Journal Classification (ASJC) codes
- 物理與天文學 (全部)