Structural, transport and magnetic studies of perovskite Bi1-x Cax Mn O3

This dissertation presents an investigation of the fundamental physics of the perovskite system Bi1-xCaxMn03. This material belongs to a group of simple perovskites called the manganites which are of technological importance for magnetic device applications as read-head sensors. The Bi1-xCaxMnO3 system is known to exhibit charge ordering (and high sensitivity to magnetic fields) for a much broader range of x than the well-characterized La1-xCaxMnO3 system. However, the properties of Bi1-xCaxMnO3 over the entire doping range are not well understood. Magnetization and resistivity measurements (up to 30T) as well as x-ray absorption and x-ray diffraction measurements on Bi1-xCaxMnO3 were performed to correlate the structural, transport, and magnetic properties. The system was found to be insulating and antiferromagnetic for the entire range of x studied (x ≥ 0.4) except near x ~ 0.875 where glassy behavior was observed. Detailed magnetization measurements were performed as a function of field and temperature to explore the net moment on the Mn sites as a function of x. These measurements reveal the charge ordering and N6el temperatures. X-ray absorption measurements reveal significant structural distortions of the Mn-0 bond distributions with increasing Bi content that correlates directly with increasing charge-ordering temperatures. Moreover, x-ray diffraction data reveal peak splittings consistent with lower symmetry cells as the Bi content increases. These structural-magnetic correlations point to the importance of Mn0 distortions in stabilizing the charge-ordered state in the manganites. A structural, transport and magnetic phase diagram over the complete range of x has been developed