Investigation of Physical Properties of Pyrochlore Iridates

Abstract

This study aims to investigate materials belonging to the pyrochlore iridate family – a class of materials with the formula A2Ir2O7 (A – trivalent ion). These materials have been the focus of a lot of research in Condensed Matter Physics because several factors such as electronic correlations, crystal fields, a geometrically frustrated lattice and spin orbit coupling act on these systems to give rise to novel behaviour. Exotic electronic ground states have been predicted to arise in these compounds as a result of the above-mentioned interplay of interactions. One of the most interesting feature displayed by these compounds is a coupled metal-to-insulator and magnetic transition, which is not very well understood. Insight into the mechanism of this transition could yield information about electronic behaviour in the presence of large spin-orbit coupling. However, it is difficult to probe into the system directly through neutron scattering because of the large neutron absorption cross section of Ir4+. Hence other methods of studying a system’s behaviour have to be resorted to. In this study, perturbation by chemical doping has been used to study the behaviour of two iridates Eu2Ir2O7 and Bi2Ir2O7 by synthesising compounds having intermediate compositions, and studying the physical properties of the resulting series. Both the samples individually display very different behaviour despite having a similar structure and non-magnetic ions on the A-site. Eu2Ir2O7 displays a metal-insulator transition at 120K accompanied by a magnetic transition into a long range ordered phase. Bi2Ir2O7, on the other hand, is metallic down to very low temperatures and also doesn’t show any magnetic ordering. This study aims to investigate the transition between the behaviours seen in these two compounds belonging to the same family. Compounds with 5, 10, 25, 50 and 75% Bismuth doping in Eu2Ir2O7 and Bi2Ir2O7 were prepared by solid state synthesis. After performing structural and compositional characterisation, their magnetic properties and electron transport properties were studied to observe how the behaviour changed across the series. The observed behavioural trends have been described in the thesis.