A Systematic Study of the Effect of Spin-Orbit Interaction on Properties of Tetravalent and Pentavalent Iridate Compounds

Author

Jasminka Terzic, University of KentuckyFollow

Date Available

12-9-2016

Year of Publication

2016

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

Abstract

Previous studies of iridates have shown that an interplay of strong SOI, Coulomb interaction U, Hund’s rule coupling and crystalline electric fields result in unexpected insulating states with complex magnetic states. The novel J_eff =1/2 insulating state first observed in Sr₂IrO₄ is a direct consequence of such an intriguing interplay and is one of the central foci of this dissertation study.

The work presented here consists of three projects: (1) Effects of Tb doping on Sr₂IrO₄ having tetravalent Ir⁴⁺(5d⁵) ions; (2) Emergence of unexpected magnetic states in double-perovskite (Ba_1-xSr_x)₂YIrO₆ with pentavalent Ir⁵⁺(5d⁴) ions in the presence of strong SOI, and (3) The coexistence of a charge and magnetic order in a magnetic dimer chain system, Ba₅AlIr₂O₁₁, which has both tetravalent Ir⁴⁺ (5d⁵) and pentavalent Ir⁵⁺ (5d⁴) ions.

A significant portion of this dissertation will focus on Tb doped Sr₂IrO₄. A central finding of this work is that slight Tb doping (3%) readily suppresses the antiferromagnetic state but retains the insulating state, indicating an unusual correlation between the magnetic and insulating states as a result of the presence of the strong SOI.

However, SOI is not the only significant phenomenon. The study on the double-perovskite (Ba_1-xSr_x)₂YIrO₆ revealed an exotic magnetic ground state, in sharp contrast to the anticipated singlet ground state in the strong SOI limit, raising an urgent question: is SOI as dominant as was initially anticipated in the iridates?

Finally, this study turns to a system containing both Ir⁴⁺ and Ir⁵⁺ ions, Ba₅AlIr₂O₁₁. This system features dimer chains of two inequivalent octahedra occupied by tetravalent Ir⁴⁺ (5d⁵) and pentavalent Ir⁵⁺ (5d⁴) ions respectively. Ba₅AlIr₂O₁₁ undergoes charge and magnetic order transitions at 210 K and 4.5 K, respectively.

SOI-driven physics is a rapidly evolving field with an ever growing list of theoretical proposals which have enjoyed very limited experimental confirmation thus far. This study has revealed a large range of interesting phenomena in the iridates that defy conventional theoretical arguments and that help to fill an experimental void in this field.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2016.488

Recommended Citation

Terzic, Jasminka, "A Systematic Study of the Effect of Spin-Orbit Interaction on Properties of Tetravalent and Pentavalent Iridate Compounds" (2016). Theses and Dissertations--Physics and Astronomy. 40.
https://uknowledge.uky.edu/physastron_etds/40