Magnetotransport and magnetic properties of La_0.7MnO_3-δ and Pr_0.65Ba_0.05Ca_0.3MnO_3-δ superlattices

Superlattice structures consisting of La_0.7MnO_3-δ (LMO) and Pr_0.65Ba_0.05Ca_0.3MnO_3-δ (PBCMO) systems, in which the thickness of La_0.7MnO_3-δ is fixed and that of Pr_0.65Ba_0.05Ca_0.3MnO_3-δ varied from 1 to 8 unit cells, have been grown in situ on (100) LaAlO₃ substrates using a pulsed-laser deposition technique. Microstructural characterization carried out on these films shows the presence of characteristic intense satellite peaks, indicating the chemical modulation of the superlattice structure. The insulator-to-metal transition and the magnetoresistance (MR) ratio are found to vary with the number of unit cells. The samples with 1, 2, 5, and 8 unit cells of Pr_0.65Ba_0.05Ca_0.3MnO_3-δ show transition temperatures of 240, 230, 150, and 160 K and MR ratios of 540%, 592%, 3150%, and 2875%, respectively. We have observed an enhancement of magnetoresistance ratios in the case of superlattices with a thickness of PBCMO greater than 5 unit cells, which may be attributed to a ferromagnetic biasing provided by the LMO layers acting as a ferromagnetic film below its transition temperature.