Degree Type

Dissertation

Date of Award

1991

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

First Advisor

David C. Johnston

Abstract

We report on the properties of La[subscript] xSr[subscript] 1-xVO[subscript]3 which has a phase diagram which is similar to Sr doped La[subscript]2CuO[subscript]4 in that it too shows a composition induced insulator to metal transition with strontium doping. In addition, the insulating compositions in the vanadium based system are antiferromagnetic and the La[subscript] xSr[subscript] 1-xVO[subscript]3 system has a perovskite structure. These features are reminiscient of the properties of the high-T[subscript] c cuprate superconductors. This makes La[subscript] xSr[subscript] 1-xVO[subscript]3 a candidate for a detailed study of its properties in order to gain a greater insight into the mechanisms at play in the high-T[subscript] c cuprate superconductors;Magnetic susceptibility, X-ray powder diffraction and [superscript]51V NMR Knight shift and relaxation rates, T[subscript]sp1-1 and T[subscript]sp2-1, are reported as functions of temperature and composition in La[subscript] xSr[subscript] 1-xVO[subscript]3. A combined analysis of the susceptibility and the [superscript]51V NMR data yields values of the density of states D([epsilon][subscript] f) and for the enhancement of the uniform susceptibility. These are indicative of a strongly exchange enhanced narrow d-band metal for x < 0.7. No evidence was found for antiferromagnetic spin fluctuations in the metallic phase nor for superconducting behaviour, in these compounds;We have extensively investigated the properties of LaVO[subscript]3. We have observed diamagnetism in this compound, which is an antiferromagnetic insulator, below the Neel temperature under field-cooled conditions. We observe hysteresis in magnetization versus applied field M(II) isotherms below the Neel temperature. LaVO[subscript]3 has a ferromagnetic component to the spin ordering, due to canting of spins and/or ferrimagnetism. Four- probe resistivity measurements rule out the possibility of superconductivity and the diamagnetism appears to be associated with ferrimagnetism in this compound. The susceptibility was found to be different below the Neel temperature under field-cooled (FC) and zero-field-cooled (ZFC) conditions. From our [superscript]51V NMR measurements on LaVO[subscript]3 we associate the kink in susceptibility with magnetic ordering.

DOI

https://doi.org/10.31274/rtd-180813-11565

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Avinash Vithal Mahajan

Language

en

Proquest ID

AAI9212165

File Format

application/pdf

File Size

110 pages

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