Transport and magnetic properties of perovskite titanium and manganese oxides

This thesis reports the study of the magnetic and transport properties of thin films and polycrystalline samples of the perovskites {dollar}rm Ndsb{lcub}1-x{rcub}Asb{lcub}x{rcub}TiOsb3{dollar} (A = Ca, Sr, Ba) and {dollar}rm Rsb{lcub}1-x{rcub}Asb{lcub}x{rcub}MnOsb3{dollar} (R = La, Pr, Nd; A = Ca, Sr, Ba). {dollar}rm Ndsb{lcub}1-x{rcub}Asb{lcub}x{rcub}TiOsb3{dollar} undergoes two metal-insulator transitions as A is varied, one on the Nd rich side (x = {dollar}sim{dollar}0.15) and one on the A rich side (x = {dollar}sim{dollar}0.85). The metallic phases behave as Fermi liquid systems where the effective mass increases as the Nd rich metal-insulator boundary is approached.; The metallic {dollar}rm Rsb{lcub}1-x{rcub}Asb{lcub}x{rcub}MnOsb3{dollar} samples show an anomalous resistivity peak near the ferromagnetic transition temperature (T{dollar}rm sb{lcub}C{rcub}),{dollar} with metal-like behavior below the peak and semiconductor-like behavior above the peak. Upon application of a magnetic field, a large drop is observed in the the electrical resistance; this is the so-called "colossal" magnetoresistance effect (CMR). The properties of the films are very sensitive to preparation details. It is observed that films grown at higher substrate temperature have a lower temperature resistivity peak (T{dollar}rm sb{lcub}P{rcub}){dollar} than the corresponding bulk samples, and after annealing the resistivity peak shifts to higher temperature. By optimizing the film preparation conditions, we have obtained a 10{dollar}sp6{dollar}% CMR effect in {dollar}rm Ndsb{lcub}0.7{rcub}Srsb{lcub}0.3{rcub}MnOsb{lcub}z{rcub}{dollar} films. Films with a low temperature resistivity peak show a large hysteresis in the resistivity. As the oxygen content of polycrystalline {dollar}rm Lasb{lcub}0.67{rcub}Basb{lcub}0.33{rcub}MnOsb{lcub}z{rcub}{dollar} decreases, the resistivity increases and both T{dollar}rm sb{lcub}P{rcub}{dollar} and T{dollar}rm sb{lcub}C{rcub}{dollar} decreases. This study suggests that large a CMR effect is associated with oxygen deficiency. Because of grain boundary effect, the polycrystalline samples show a large low field magnetoresistance effect at low temperature and different resistivity behavior than the films. We do found that samples with a magnetization smaller than the full theoretical saturation value exhibit anomalous magnetic behavior such as spin freezing, enhanced coercivity. A possible cause of CMR and other anomalous behavior in these materials is discussed.