Topotactic synthesis and characterization of new Kitaev iridates

  • Quantum phenomena hold a strong promise for new innovative technologies. Experimental realization of these phenomena in solid-state materials is particularly important for eventual practical applications. A special place among the class of inorganic materials is taken by transition metal oxides (TMO) providing a rich variety of physical phenomena. The interplay between Coulomb correlations, bandwidth and spin-orbit coupling (SOC) gives rise to some extraordinary electronic and magnetic properties such as high-temperature superconductivity, charge density waves, magnetic skyrmions and frustrated magnetism. The latter one found for the antiferromagnetic Mott insulators is of particular interest as it can lead to a new unusual state known as a quantum spin liquid (QSL). The allure of frustrated spin systems is that they may develop not a magnetically ordered ground state as in conventional magnets, but a paramagnetic-like state down to 0 K, where spins continually fluctuate. OriginallyQuantum phenomena hold a strong promise for new innovative technologies. Experimental realization of these phenomena in solid-state materials is particularly important for eventual practical applications. A special place among the class of inorganic materials is taken by transition metal oxides (TMO) providing a rich variety of physical phenomena. The interplay between Coulomb correlations, bandwidth and spin-orbit coupling (SOC) gives rise to some extraordinary electronic and magnetic properties such as high-temperature superconductivity, charge density waves, magnetic skyrmions and frustrated magnetism. The latter one found for the antiferromagnetic Mott insulators is of particular interest as it can lead to a new unusual state known as a quantum spin liquid (QSL). The allure of frustrated spin systems is that they may develop not a magnetically ordered ground state as in conventional magnets, but a paramagnetic-like state down to 0 K, where spins continually fluctuate. Originally proposed for the triangular antiferromagnets in which the source of magnetic moments was 3d-transition metals, the idea of magnetic frustration and experimental realization of QSL was transposed onto other frustrated lattices such as Kagome or pyrochlore ones. However, the heavy 4d- and 5d-TMO with a strong effect of SOC have been out of sight of the fast-developing spin-liquid physics until the moment when A. Kitaev formulated the model, now commonly known as the Kitaev model, on the hexagonal (honeycomb) lattice with a QSL ground state and fractionalized Majorana-like excitations. Further development of the Kitaev model by G. Jackeli and G. Khaliullin for real materials outlined the compound families that are most promising new QSL-candidates. Thus, the honeycomb layered iridates Na2IrO3 and alpha-Li2IrO3 were recognized as promising Kitaev spin-liquid materials. Unfortunately, the comprehensive study of sodium and lithium iridates has shown that these compounds develop long-range magnetic order and deviate from scenario of Kitaev spin liquid. This problem identifies the need for isoelectronic iridates with the honeycomb geometry or with other tricoordinated lattices of Ir(4+). However, only a handful of such compounds is known from the literature. Beyond Na2IrO3 and alpha-Li2IrO3, they include two other polymorphs of Li2IrO3 only. Attempts of partial chemical substitutions, as in (Li,Na)2IrO3, were only partially successful, given the large miscibility range of the corresponding solid solution. All of this calls for new chemical strategies that may stabilize hitherto unknown metastable iridates with the honeycomb or honeycomb-like geometry of Ir(4+). One important prerequisite of such compounds should be the absence of structural disorder, because randomness of exchange interactions can also suppress magnetic order, similar to the frustration, yet without creating the desired QSL ground state. To this end, we implement the technique of topotactic chemical reactions that entail the ion exchange performed under mild heating and result in completely new chemical compounds that preserve the structural network of their precursor. To avoid structural disorder, we concentrate on beta-Li2IrO3, which is widely available in both polycrystalline and single-crystalline form without any appreciable structural defects. The focus of this thesis is on three compounds prepared for the first time, their structural and magnetic characterization.show moreshow less

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Metadaten
Author:Aleksandr ZubtsovskiiORCiD
URN:urn:nbn:de:bvb:384-opus4-963675
Frontdoor URLhttps://opus.bibliothek.uni-augsburg.de/opus4/96367
Advisor:Alexander Tsirlin
Type:Doctoral Thesis
Language:English
Year of first Publication:2022
Publishing Institution:Universität Augsburg
Granting Institution:Universität Augsburg, Mathematisch-Naturwissenschaftlich-Technische Fakultät
Date of final exam:2022/06/23
Release Date:2022/08/30
Tag:Frustrated magnetism; Topotactic synthesis; Kitaev iridates; Dimerization transition
GND-Keyword:Iridate; Geometrische Frustration; Topotaktische Reaktion; Stoffeigenschaft
Pagenumber:vi, 114
Institutes:Mathematisch-Naturwissenschaftlich-Technische Fakultät
Mathematisch-Naturwissenschaftlich-Technische Fakultät / Institut für Physik
Mathematisch-Naturwissenschaftlich-Technische Fakultät / Institut für Physik / Lehrstuhl für Experimentalphysik VI
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften
Licence (German):CC-BY-NC-SA 4.0: Creative Commons: Namensnennung - Nicht kommerziell - Weitergabe unter gleichen Bedingungen (mit Print on Demand)