Publication Date

2021

Document Type

Dissertation/Thesis

First Advisor

Chmaissem, Omar

Degree Name

Ph.D. (Doctor of Philosophy)

Legacy Department

Department of Physics

Abstract

The exciting field of iron-pnictide superconductors offers unique opportunities for studying the relationship between magnetism and unconventional superconductivity. This is vital to developing an understanding of the microscopic origin of high-temperature superconductivity, which is itself an important step in harnessing such a potentially revolutionary technology.

Polycrystalline and crystalline samples are synthesized over a diverse collection of related iron-pnictide systems including (Ca,Sr,Ba)1-xNaxFe2As2, Ba(Fe1-xCox)2As2 (122s), and LaFeAs1-xPxO, and TbFeAs1-xPxO (1111s). These compounds are characterized through various types of neutron and x-ray diffraction on multiple instruments, as well as muon spin resonance, and magnetic susceptibility measurements.

A thorough investigation into the conditions under which the in-plane orthorhombic and out-of-plane tetragonal magnetic phases arise in the hole-doped 122s allows the construction of a predictive universal phase diagram for this sub-family. With the first exploration of the full LaFeAs1-xPxO phase diagram by neutron and x-ray diffraction, we discover three magnetic phases in this system: the two aforementioned that are shared with the 122s along with an intermediary in-plane tetragonal phase. The in-plane and out-of-plane tetragonal magnetic phases had previously only been detected in the electron-doped CaKFe4As4 (1144s) and hole-doped 122s respectively. We support the experimentally-determined evolution of these magnetic phases with a theoretical model taking into account spin-orbit coupling that agrees with our results. Our analysis is culminated in the identification of disorder as a hidden tuning parameter to account for the detected electronic states. With the commonalities we discover between the 122, 1144, and 1111 families, we are able to draw general conclusions regarding the relationship between superconductivity and magnetism in the various iron-pnictide systems; this is a vital clue to producing a fully realized microscopic theory of iron-base superconductivity.

Extent

184 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

Download

Share

COinS