In the context of the search and tuning for novel magnetic materials, transition metal compounds exhibit remarkable features where the spin-orbit interaction is crucial. The collective interactions between various effects, like spins and charges, create different classes of unique magnetic systems. For heavy transition-metal compounds, the strength of spin-orbital coupling is enhanced. The jeff. = 1/2 Mott insulating state emerges from the combination of the spin-orbit interaction and the electronic correlations. The quantum-chemistry methods are employed in this thesis to investigate single- and two-site magnetic interactions of the selected transition-metal compounds. We also provide different estimations for the single- and two-site magnetic interactions based on the level of calculation accuracy.
In this thesis, we apply ab initio quantum-chemistry methods to explore the electronic and magnetic properties of several d/f compounds. The thesis structure is as follows:
In Chapter 1, the introduction of the thesis provides a short discussion of the electronic correlations and magnetism in transition metal compounds. In Chapter 2, the fundamentals of the quantum chemistry wavefunction-based approach are covered. This chapter gives an overview of the applied methods in this thesis.
In Chapter 3, we discuss the quantum chemistry approach to investigate the material candidates to host Kitaev physics. The technique to obtain the strength of two-site magnetic couplings, including the Kitaev coupling, is discussed in-depth.
In Chapter 4, we apply the technique, which is described in Chapter 3, to investigate the two-site magnetic interactions in the H3LiIr2O6, and Cu2IrO2 compounds as Kitaev candidates. The two-site magnetic couplings are reported in these compounds.
In Chapter 5, we use quantum chemistry methods to investigate the on-site electronic and magnetic properties in the KCeO2 compound where 4f1 Ce3+ ions form a triangular two-dimensional lattice with sites of effective spin-1/2. Similar ytterbiumbased delafossites had been investigated as candidates for quantum spin liquid ground states. The absence of ordinary magnetic order is characteristic of quantum spinliquid states where quantum entanglements and fractionalized excitations are enriched.
In Chapter 6, the magnetic properties of Co 3d8 ions doped in the Li3N crystalline solid are discussed. The results of the quantum chemistry investigation are been set side by side along with the experiment’s results. The Co ion in such a rare environment gives rise to single-site magnetism of an easy-plane anisotropy.:Table of Contents . . . . . . . . . . . . . . . . . . . . . . iv
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . .vi
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i
Acknowledgements . . . . . . . . . . . . . . . . . . . . . .iii
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
1.1 Electronic correlations and magnetism in transition metal compounds ...........1
1.2 Thesis outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Quantum chemistry methodology . . . . . . . . . . . . . . . . .6
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Many-electron Hartree-Fock approximation . . . . . . . . . . . . . . . 9
2.3 Multi-configurational self-consistent field and multi-reference configuration
methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 Spin-orbit interaction and g-factors calculation . . . . . . . . . . . . . 15
2.5 Embedded cluster approach . . . . . . . . . . . . . . . . . . . . . . . 18
2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3 Quantum chemistry investigation of Kitaev material candidates . . . . . . . . . . .21
3.1 Introduction to the Kitaev model . . . . . . . . . . . . . . . . . . . . 23
3.2 Kitaev materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3 Two-site quantum chemistry calculations . . . . . . . . . . . . . . . . 36
3.4 Effective Model of Two Spin-1/2 . . . . . . . . . . . . . . . . . . . . . 38
3.5 Non-canonical correspondence between two-site QC results and the
effective Hamiltonian . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.6 Pseudospin coordinate system and canonical correspondence between
two-site QC results and the effective Hamiltonian . . . . . . . . . . . 51
3.7 Signs of the g-tensor in the Kitaev limit . . . . . . . . . . . . . . . . 53
3.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4 Kitaev material candidates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.2 Details of QC calculations . . . . . . . . . . . . . . . . . . . . . . . . 64
4.3 QC investigation of H3LiIr2O6 . . . . . . . . . . . . . . . . . . . . . . 66
4.4 QC investigation of Cu2IrO3 . . . . . . . . . . . . . . . . . . . . . . . 75
4.5 Impact of local symmetries on the obtained sets of magnetic couplings ......... 82
4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5 Ce ions in two-dimensional triangular spin-1/2 lattices . . . . . . . . . . . . . . . . . . . . 89
5.1 Spin-1/2 frustrated triangular lattice . . . . . . . . . . . . . . . . . . 90
5.2 Correlated 4f -compounds as frustrated triangular lattices . . . . . . 94
5.3 Crystal structure of KCeO2 . . . . . . . . . . . . . . . . . . . . . . . 95
5.4 QC results for the electronic structure of Ce3+ ions in KCeO2 . . . . 100
5.5 The competition of SOC and crystal field splittings in KCeO2 . . . . 102
5.6 Chapter summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
6 Co-ion substitutes with linear coordination in Li3N . . . . . . . . . . . . . . . . . . . . . . 109
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
6.2 Crystal structure of Li2(Li(1−x)Cox)N and spectroscopic measurements .......112
6.3 QC computational details . . . . . . . . . . . . . . . . . . . . . . . . 115
6.4 Ab initio QC investigation of the Co+ 3d8 electronic structure doped into Li3N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
6.5 Chapter summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:92328 |
| Date | 09 July 2024 |
| Creators | Eldeeb, Mohamed Sabry |
| Contributors | van den Brink, Jeroen, Lounis, Samir, Technische Universität Dresden, IFW Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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