A SYSTEMATIC STUDY OF THERMODYNAMIC AND TRANSPORT PROPERTIES OF LAYERED 4D AND 5D CORRELATED ELECTRON SYSTEMS

Author

Shalinee Chikara, Univeristy of KentuckyFollow

Date Available

3-28-2012

Year of Publication

2011

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Arts and Sciences

Department

Physics and Astronomy

First Advisor

Prof. Gang Cao

Abstract

Correlated electron materials have been at the forefront of condensed matter research in the past couple of decades. Correlation in materials, especially, with open d and f electronic shells often lead to very exciting and intriguing phenomenon like high temperature superconductivity, Mott metal-insulator transition, colossal magnetoresistance (CMR). This thesis focuses on triple-layered Sr₄Ru₃O₁₀, Sr substituted double layered (Ca1-- xA_x)₃Ru₂O₇ (A = Ba, Sr) and 5d system Sr₂IrO₄ and Sr₃Ir₂O₇. Triple-layered Sr₄Ru₃O₁₀ displays interesting phenomena ranging from quantum oscillations, tunneling magnetoresistance, unusual low temperature specific heat, strong spin-lattice coupling to switching behavior. The central feature, however, is the unique borderline magnetism: along the c-axis. Sr₄Ru₃O₁₀ shows spontaneous ferromagnetism, indicating a strong Coulomb exchange interaction, U and a large density of states at the Fermi surface, g(E_F ), hence Ug(E_F ) ≥ 1 (Stoner criterion). But within the ab-plane it features a pronounced peak in magnetization and a first-order metamagnetic transition. The coexistence of the interlayer ferromagnetism and the intralayer metamagnetism makes Sr₄Ru₃O₁₀ a really unique system. Also, in this thesis the spin-valve behavior exhibited by impurity doping at the Ca site by Ba and Sr in the double layered Ca₃Ru₂O₇ is reported. Spin valve effect is a phenomenon only realized in multilayer thin films. Here, spin valve is observed in bulk single crystals of impurity dopedCa₃Ru₂O₇, Ca₃(Ru_1-xCr_x)₂O₇ and (Ca1- xA_x)₃Ru₂O₇ (A = Ba, Sr). 5d Iridates are expected to be more metallic and less magnetic than their 3d and 4f counterparts because of the extended 5d orbitals. In marked contrast, many iridates are magnetic insulators with exotic properties. The focus in this thesis is on Sr2IrO4 which diplays a novel J_eff = 1/2 Mott state. Magnetic, electrical, and thermal measurements on single-crystals of Sr₂IrO₄, reveal a novel giant magneto-electric effect (GME) arising from a frustrated magnetic/ferroelectric state. The GME and electric polarization hinge on a spin-orbit gapping of 5d-bands, rather than the magnitude and spatial dependence of magnetization, as traditionally accepted.

Recommended Citation

Chikara, Shalinee, "A SYSTEMATIC STUDY OF THERMODYNAMIC AND TRANSPORT PROPERTIES OF LAYERED 4D AND 5D CORRELATED ELECTRON SYSTEMS" (2011). University of Kentucky Doctoral Dissertations. 843.
https://uknowledge.uky.edu/gradschool_diss/843