Influence of Varying Grain Size on Electrical, Microstructural and Transport Properties of Nd0.68Sr0.32MnO3

A study of Nd0.68Sr0.32MnO3 manganite has been undertaken to understand the influence of varying grain size on the electrical, microstructural and magneto transport properties. The materials were prepared via solid state reaction method with sintering at 1170, 1270 and 1350 oC. The XRD patterns confirmed that all samples have a single phase with orthorhombic structure. The grain size was 1.0, 1.2 and 1.4 μm for samples sintered at 1170, 1270 and 1350 oC, respectively. Grain size is found to increase linearly with sintering temperature and inversely proportional to To values, where the To value reflects the bending of Mn-O-Mn bond angle. The insulator metal transition temperature, Tim is ~ 205 K for samples sintered at 1270 oC and 1350 oC. The grains growth with a spiral pattern along a favorable direction may have shifted Tim to higher temperature region for sample sintered at 1270 oC. For sample sintered at 1170 oC, Tim was around 180 K. The metallic and insulating regime of the resistivity can be fitted with several equations and models that were used. MR measurements were carried out in the applied magnetic field up to 1 Tesla at room temperature. The MR values are found to increase with increasing magnetic field. This may be attributed to the suppression of magnetic spins scattering with the application of magnetic field. Sample sintered at 1170 oC showed the highest MR of ~ 10 % in 1 T magnetic field.