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

Tribological Studies of Ultra-Thin Films at Head/Media Interface for Magnetic Data Storage Systems

Ph.DDOCTOR OF PHILOSOPH

Innovations in the Design of Magnetic Tape Subsystems

This paper explores the selection of magnetic tape as an inputloutput medium for electronic computers and reviews the innovations in the development of magnetic tape and tape handling machines since their introduction in the early 1950s