Low-Field Magnetoresistance in Nanocomposites of La₀.₇Sr₀.₃MnO₃ and Metal Oxides

Pure La0.7Sr0.3MnO3 (LSMO) exhibits colossal magnetoresistance (CMR) with large applied magnetic field over a narrow temperature range (intrinsic behavior), limiting its application to narrow temperature ranges. In contrast, the extrinsic CMR effect originates from inhomogeneities at larger length scales, such as grain boundaries and phase separation, where the structural features act as tunneling barriers, leading to a low-field magnetoresistance (LFMR) response, thereby expanding the application of LSMO into the low-field regime over a broader temperature range. In this work, the magnetotransport behavior of pure LSMO thin film is compared to the composite layered heterostructures of LSMO and either TiO2 or MgO, as well as a homogenous composite of LSMO and TiO2 grown on (001)-oriented LaAlO3 substrates. Samples were synthesized via chemical solution deposition and characterized for their structural, microstructural, and magnetotransport properties. Pure LSMO exhibits a ferromagnetic to paramagnetic transition at 366 K, which decreases in all TiO2-related nanocomposite films but remains similar for LSMO:MgO film. Magnetoresistance (MR) values were determined via temperature-dependent and field-dependent resistivity measurements. The maximum MR value for LSMO was –20.5% with applied field of 3 T, which shows a sharp peak at the metal-insulator transition (intrinsic behavior). For the LSMO:TiO2 (60:20), LSMO:TiO2 (50:20), LSMO:MgO (50:20), and homogenous LSMO:TiO2 (10:1) nanocomposite films, maximum MR values at 3 T were -9.4%, -21%, -17%, and -30.7%, respectively. Among these composite films, only LSMO:MgO film showed peak MR near the transition temperature (intrinsic), otherwise all TiO2-related nanocomposite films exhibited extrinsic behavior (broader MR peak and non-zero MR at low temperatures). Homogeneous LSMO:TiO2 film showed the largest magnetoresistance among the films studied in this work. These have potential to be used in magnetic sensors and spintronic devices.