Investigation of CMR Properties in Perovskite Manganites.

The interesting interactions among charge, spin and lattice degrees of freedom make the perovskite-based colossal magnetoresistance (CMR) materials very attractive for theoretical and experimental investigation. Since the discovery of CMR materials, there has been extensive study on these materials because of their novel physical properties and potential applications. The physical properties of these samples are usually dependent on their preparation routes. In the present work, nanosized La0.7Sr0.3MnO3 (LSMO) and La0.67Ca0.33 MnO3 (LCMO) perovskite oxides were prepared at relatively low calcined temperature and the structural, magnetic and transport properties were studied and reviewed. The size and topography of the oxides are dependent on the calcinating temperature of the precursors. The magnetization of LSMO and LCMO nanophase is strikingly dependent on the particle size. The transport and magnetoresistive properties of the samples are strongly depend on the sintering temperature. A substantial decrease in the insulator-metal transition temperature and an enhancement in resistivity are found on lowering the sintering temperature. LSMO and LCMO shows enhanced ferromagnetic transition temperature as high as 372 and 265 K respectively. Furthermore, it is also well known that the materials should be in the form of thin film in view with the practical application. So the thin films of LSMO and LCMO were fabricated on Si substrate using this nano-sized powder compacted target. It is observed that film exhibiting CMR can be grown on Si(100) without any buffer layer using this nanosized powder compacted target material. The effects of annealing on the properties of LSMO and LCMO thin film are also reviewed here. As-grown films show a lower metal-insulator transition (TMI) temperature than annealed films. As the annealing temperature increases, significantly higher TMI values are observed. We suggest that the increase of effective hole doping, induced by cationic vacancies due to the excess oxygen, is a possible reason for the observed trend in TMI. Annealing improves the magnetic homogeneity of the grain and grain boundaries. These improvements are favorable to enhance the intrinsic properties of the compound especially the decrease of resistivity. The decrease in resistivity induces the MR ratio to increase. [ABSTRACT FROM AUTHOR]