In this thesis we have investigated the effect of Ti 4+ substitution and preparation conditions on the structural, magnetic and electrical properties of La 0.8 Sr 0.2 Mn 1-x Ti x O 3 (0.00?x?0.075) manganite. The samples have been prepared by the standard solid state reaction method. In order to investigate the effect of sintering temperature on various properties of samples, the samples divided into two series and sintered at 1200(LT) and 1400(HT) centigrade. The analysis of the XRD pattern showed that all samples have rhombohedral structure and Ti 4+ substitution has no considerable effect on the samples structure, but it just changed the peaks positions. The SEM images show that the magnitude of grain size in HT samples is large compared to LT samples. The AC magnetic susceptibility measurements showed that the Curie temperature decreases with increasing of the Ti 4+ content, and this means that the double exchange diminishes by titanium doping into the samples. In the x=0.05 and x=0.075 of HT samples, the ferromagnetic long range ordering is no longer stable after paramagnetic-ferromagnetic transition. and these samples show antiferomagnetic transition at low temperatures. the x=0.075 of LT sample and x=0.05 and x=0.075 of HT samples, show a drop in the real part of AC susceptibility and a peak in the imaginary part of AC magnetic susceptibility curves. The peak is related to spin glass state in these samples.
