Observation and control of the low temperature superstructure in manganites

• Main Author: Cox, S.
• Published: University of Cambridge 2006
• Subjects: 530.417
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598107

The work in this dissertation is focused on the insulating side of the La_1-xCa_xMnO₃ and Pr_1-xCa_xMnO₃ phase diagram, in particular on the low temperature ‘charge ordered’ phase. This phase exhibits a superstructure whose periodicity depends on the doping of the sample, among other factors. Firstly the microscopic nature of the charge ordered phase is probed using a variety of techniques including TEM, heat capacity measurements and neutron diffraction measurements. Secondly, the charge ordered phase is controlled via the manipulation of strain. In the first set of experiments, polycrystalline samples are subject to extrinsic effects, and so although it is possible to observe spatial variations in the superstructure, it is not possible to systematically control possible causes of the variation. By growing thin films it was possible to control the level of strain in the film, which is one of the extrinsic effects. This creates a spatial variation in the superstructure which could be observed. The results of this experiment can then be used to provide insight into the small scale nature of the charge ordering superstructure.