A Systematic Transport and Thermodynamic Study of Heavy Transition Metal Oxides with Hexagonal Structure

Author

Kamal H. Butrouna, University of KentuckyFollow

Date Available

7-8-2014

Year of Publication

2014

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Physics and Astronomy

First Advisor

Dr. Gang Cao

Second Advisor

Dr. Lance De Long

Abstract

There is no apparent, dominant interaction in heavy transition metal oxides (TMO), especially in 5d-TMO, where all relevant interactions are of comparable energy scales, and therefore strongly compete. In particular, the spin-orbit interaction (SOI) strongly competes with the electron-lattice and on-site Coulomb interaction (U). Therefore, any tool that allows one to tune the relative strengths of SOI and U is expected to offer an opportunity for the discovery and study of novel materials. BaIrO₃ is a magnetic insulator driven by SOI whereas the isostructural BaRuO₃ is a paramagnetic metal. The contrasting ground states have been shown to result from the critical role of the strong SOI in the iridate. This dissertation thoroughly examines a wide array of newly observed novel phenomena induced by adjusting the relative strengths of SOI and U via a systematic chemical substitution of the Ru⁴⁺(4d⁴) ions for Ir⁴⁺(5d⁵) ions in BaIrO₃, i.e., in high quality single crystals of BaIr_1-xRu_xO₃(0.0 < x < 1.0) . Our investigation of structural, magnetic, transport and thermal properties reveals that Ru substitution directly rebalances the competing energies so profoundly that it generates a rich phase diagram for BaIr_1-xRu_xO₃ featuring two major effects: (1) Light Ru doping (0 < x < 0.15) prompts a simultaneous and precipitous drop in both the magnetic ordering temperature T_C and the electrical resistivity, which exhibits metal-insulator transition at around T_C. (2) Heavier Ru doping (0.41 < x < 0.82) induces a robust metallic and spin frustration state. For comparison and contrast, we also substituted Rh⁴⁺(4d⁵) ions for Ir⁴⁺(5d⁵) ions in BaIrO₃, i.e. BaIr_1-xRh_xO₃(0.0 < x < 0.10), where Rh only reduces the SOI, but without altering the band filling. Hence, this system remains tuned at the Mott instability and is very susceptible to disorder scattering which gives rise to Anderson localization.

Recommended Citation

Butrouna, Kamal H., "A Systematic Transport and Thermodynamic Study of Heavy Transition Metal Oxides with Hexagonal Structure" (2014). Theses and Dissertations--Physics and Astronomy. 24.
https://uknowledge.uky.edu/physastron_etds/24