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A Comprehensive Experimental Approach to Multifunctional Quantum Materials and their Physical Properties: Geometry and Physics in Condensed Matter
KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. (Sustainable Materials Research & Technologies (SMaRT))ORCID iD: 0000-0003-4441-8882
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis ranges within the vast framework of experimental condensed matter physics. Several different systems, and physical phenomena, are presented here from a structuralist standpoint. In fact, we show how, in solid condensed matter, the underlying arrangement of atoms, the symmetry of their structure, and their mutual interactions, underpin the form and the nature of their collective emergent properties. Our effort in this work was focused on unveiling complex magnetic ground states in newly synthesized materials, as well as in the clarification of unconventional symmetry breaking phenomena in highly debated systems. In all cases, we could understand the physics of such systems only when we elucidated the details, and temperature dependent evolution, of their structures.

About the choice of target materials for our investigations, our starting point has not only been fundamental condensed matter physics, but also forward looking towards a sustainable future. Here we considered both the development of energy efficient spintronics and quantum computing, as well as the need for efficient conversion and storage of clean energy. Therefore, this project is concerned with the advanced characterization of novel ”multifunctional” materials, that constitute a unique playground for fundamental scientific research, but also lend themselves to potential novel technical applications. Such materials might indeed display high temperature dynamical properties, which make them suitable for rechargeable batteries and heat conduction applications. At the same time, they are also strongly correlated electron systems at lower temperatures, and their fundamental magnetic and electronic properties are relevant for the development of quantum devices. To explore these properties, extensive experimental studies using large-scale research facilities were employed. In this project, several unique and powerful state-of-the-art high-resolution neutron scattering, X-ray scattering, and muon spin rotation techniques were used.

Place, publisher, year, edition, pages
Stockholm: Kungliga Tekniska högskolan, 2022. , p. 137
Series
TRITA-SCI-FOU ; 2022:58
Keywords [en]
quantum materials, neutron, muon, X-ray, symmetry, phase transitions
National Category
Condensed Matter Physics
Research subject
Physics, Material and Nano Physics
Identifiers
URN: urn:nbn:se:kth:diva-321992ISBN: 978-91-8040-420-4 (print)OAI: oai:DiVA.org:kth-321992DiVA, id: diva2:1713829
Public defence
2022-12-19, (Room 4204), Hannes Alfvéns väg 12, vån. 4, Alba Nova, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2022-11-28 Created: 2022-11-28 Last updated: 2023-12-07Bibliographically approved
List of papers
1. Revised Magnetic structure and tricritical behavior of the CMR Compound NaCr2O4 investigated with High Resolution Neutron Diffraction and μ+SR.
Open this publication in new window or tab >>Revised Magnetic structure and tricritical behavior of the CMR Compound NaCr2O4 investigated with High Resolution Neutron Diffraction and μ+SR.
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321683 (URN)
Note

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2024-05-21Bibliographically approved
2. Na-ion Dynamics in the Solid Solution NaxCa1-xCr2O4 Studied by Muon Spin Rotation and Neutron Diffraction
Open this publication in new window or tab >>Na-ion Dynamics in the Solid Solution NaxCa1-xCr2O4 Studied by Muon Spin Rotation and Neutron Diffraction
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this work we present systematic set of measurements carried out by muon spin rotation/relaxation (μ+SR) and neutron powder diffraction (NPD) on the solid solution NaxCa1−xCr2O4. This study investigates Na-ion dynamics in the quasi-1D (Q1D) diffusion channels created by the honeycomb-like arrangement of CrO6 octahedra, in the presence of defects introduced by Ca doping. With increasing Ca content, the size of the diffusion channels is enlarged, however, this effect does not enhance the Na ion mobility. Instead the overall diffusivity is hampered by the local defects and the Na hopping probability is lowered. The diffusion mechanism in NaxCa1−xCr2O4 was found to be interstitial and the activation energy as well as diffusion coefficient were determined for all the members of the solid solution. 

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321685 (URN)10.48550/arXiv.2211.13164 (DOI)
Note

Submitted to  Sustainable Energy & Fuels, E-ISSN 2398-4902

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2024-02-05Bibliographically approved
3. Pressure Dependent Magnetic properties of the Q1D Solid Solution Ca1-xNaxCr2O4 Studied with Neutrons Muons and X-Rays
Open this publication in new window or tab >>Pressure Dependent Magnetic properties of the Q1D Solid Solution Ca1-xNaxCr2O4 Studied with Neutrons Muons and X-Rays
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321686 (URN)
Note

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2023-12-07Bibliographically approved
4. Neutron powder diffraction study of NaMn2O4 and Li0.92Mn2O4 : Insights on spin-charge-orbital ordering
Open this publication in new window or tab >>Neutron powder diffraction study of NaMn2O4 and Li0.92Mn2O4 : Insights on spin-charge-orbital ordering
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2020 (English)In: Physical Review Research, E-ISSN 2643-1564, Vol. 2, no 4, article id 043143Article in journal (Refereed) Published
Abstract [en]

High-pressure synthesized quasi-one-dimensional NaMn2O4 and Li0.92Mn2O4 are both antiferromagnetic insulators. Here their atomic and magnetic structures are investigated using neutron powder diffraction. The present crystal structural analyses of NaMn2O4 reveal that a Mn3+/Mn4+ charge-ordering state exists even at low temperature (down to 1.5 K). It is evident that one of the Mn sites shows a strongly distorted Mn3+ octahedron due to the Jahn-Teller effect. Above TN=35 K, a two-dimensional short-range correlation is observed, as indicated by asymmetric diffuse scattering. Below TN, two antiferromagnetic transitions are observed: (i) a commensurate long-range Mn3+ spin ordering below TN1=35 K and (ii) an incommensurate Mn4+ spin ordering below TN2=11 K. Surprisingly, the two antiferromagnetic orders are found to be independent of each other. The commensurate magnetic structure (kC=0.5,0.5,0.5) follows the magnetic anisotropy of the local easy axes of Mn3+, while the incommensurate Mn4+ one shows a spin-density-wave or a cycloidal order with kIC=(0,0,0.216). For Li0.92Mn2O4, on the other hand, the absence of a long-range spin-ordered state is confirmed down to 1.5 K.

Place, publisher, year, edition, pages
American Physical Society (APS), 2020
Keywords
Binary alloys; Crystal atomic structure; Crystallography; Density (optical); Magnetic anisotropy; Magnetic structure; Neutron powder diffraction; Spin density waves; Temperature
National Category
Natural Sciences Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-321681 (URN)10.1103/physrevresearch.2.043143 (DOI)000605400600002 ()2-s2.0-85115906902 (Scopus ID)
Funder
Swedish Foundation for Strategic ResearchSwedish Research Council, 2016-06955Swedish Research Council, 201705078Swedish Foundation for Strategic ResearchSwedish Research Council, 2016-06955Swedish Research Council, 201705078Swedish Foundation for Strategic ResearchSwedish Research Council, 2016-06955Swedish Research Council, 201705078
Note

QC 20221124

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2023-12-07Bibliographically approved
5. Superconducting Properties of the Thin Film LiTi2O4 Spinel Compound Investigated by Low-Energy µ+SR
Open this publication in new window or tab >>Superconducting Properties of the Thin Film LiTi2O4 Spinel Compound Investigated by Low-Energy µ+SR
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321690 (URN)
Note

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2023-12-07Bibliographically approved
6. Nuclear and magnetic spin structure of the antiferromagnetic triangular lattice compound LiCrTe2 investigated by µ+SR, neutron and X-ray diffraction
Open this publication in new window or tab >>Nuclear and magnetic spin structure of the antiferromagnetic triangular lattice compound LiCrTe2 investigated by µ+SR, neutron and X-ray diffraction
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Two−dimensional (2D) triangular lattices antiferromagnets (2D−TLA) often manifest intriguing physical and technological properties, due to the strong interplay between lattice geometry and electronic properties. The recently synthesized 2−dimensional transition metal dichalcogenide LiCrTe2, being a 2D−TLA, enriched the range of materials which can present such properties. In this work, muon spin rotation (μ+SR) and neutron powder diffraction (NPD) have been utilized to reveal the true magnetic nature and ground state of LiCrTe2. From high−resolution NPD the magnetic spin order at base−temperature is not, as previously suggested, helical, but rather collinear antiferromagnetic (AFM) with ferromagnetic (FM) spin coupling within the ab−plane and AFM coupling along the c−axis. The ordered magnetic Cr moment is established as μCr= 2.36 μB. From detailed μ+SR measurements we observe an AFM ordering temperature TN≈ 125 K. This value is remarkably higher than the one previously reported by magnetic bulk measurements. From μ+SR we are able to extract the magnetic order parameter, whose critical exponent allows us to categorize LiCrTe2 in the 3D Heisenberg AFM universality class. Finally, by combining our magnetic studies with high−resolution synchrotron X−ray diffraction (XRD), we find a clear coupling between the nuclear and magnetic spin lattices. This suggests the possibility for a strong magnon−phonon coupling, similar to what has been previously observed in the closely related compound LiCrO2.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321692 (URN)10.48550/arXiv.2210.14079 (DOI)
Note

Published in Scientific Reports DOI: 10.1038/s41598-022-25921-9

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2024-02-05Bibliographically approved
7. The Duel of Magnetic Interactions and Structural Instabilities: Itinerant Frustration in the Triangular Lattice Compound LiCrSe2
Open this publication in new window or tab >>The Duel of Magnetic Interactions and Structural Instabilities: Itinerant Frustration in the Triangular Lattice Compound LiCrSe2
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The recent synthesis of the chromium selenide compound LiCrSe2 constitutes a valuable addition to the ensemble of two-dimensional triangular lattice antiferromagnets (2D-TLA). In this work we present the very first comprehensive study of the combined low temperature nuclear and magnetic structure established in this material. Details on the connection between Li-ion dynamics and structural changes are also presented along with a direct link between atomic structure and spin order via a strong magnetoelastic coupling. LiCrSe2 was found to undergo a first order structural transition from a trigonal crystal system with space group P3¯m1 to a monoclinic one with space group C2/m at Ts=30~K. Such restructuring of the lattice is accompanied by a magnetic transition at TN=30~K, with the formation of a complex spin arrangement for the Cr3+ moments. Refinement of the magnetic structure with neutron diffraction data and complementary muon spin rotation analysis reveal the presence of two incommensurate magnetic domains with a up-up-down-down arrangement of the spins with ferromagnetic (FM) double chains coupled antiferromagnetically (AFM). In addition to this unusual arrangement, the spin axial vector is modulated both in direction and modulus, resulting in a spin density wave-like order with periodic suppression of the Cr moment along the chains. This behavior is believed to appear as a result of strong competition between direct exchange AFM and superexchange FM couplings established between both nearest neighbor and next nearest neighbor Cr3+ ions. We finally conjecture that the resulting magnetic order is stabilized via subtle vacancy/charge order within the Li layers, potentially causing a mix of two different magnetic phases within the sample.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321697 (URN)10.48550/arXiv.2211.06864 (DOI)
Note

Published in Communications Materials DOI: 10.1038/s43246-023-00407-x

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2024-02-05Bibliographically approved
8. Cr-Cr Distance and Magnetism in the Novel Triangular Lattice Antiferromangets LiCrSe2, LiCrTe2 and NaCrTe2: a systematic µ+SR study
Open this publication in new window or tab >>Cr-Cr Distance and Magnetism in the Novel Triangular Lattice Antiferromangets LiCrSe2, LiCrTe2 and NaCrTe2: a systematic µ+SR study
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321701 (URN)
Note

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2023-12-07Bibliographically approved
9. Magnetic nature of wolframite MgReO4
Open this publication in new window or tab >>Magnetic nature of wolframite MgReO4
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(English)In: ISSN 2165-5286Article in journal (Other academic) Accepted
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321703 (URN)10.48550/arXiv.2209.11966 (DOI)
Note

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2023-12-07Bibliographically approved
10. Structural Evolution and Onset of the Density Wave Transition in the CDW Superconductor LaPt2Si2 Clarified with Synchrotron XRD
Open this publication in new window or tab >>Structural Evolution and Onset of the Density Wave Transition in the CDW Superconductor LaPt2Si2 Clarified with Synchrotron XRD
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The quasi-2D Pt-based rare earth intermetallic material LaPt2Si2 has attracted attention as it exhibits strong interplay between charge density wave (CDW) and and superconductivity (SC). However, the most of the results reported on this material come from theoretical calculations, preliminary bulk investigations and powder samples, which makes it difficult to uniquely determine the temperature evolution of its crystal structure and, consequently, of its CDW transition. Therefore, the published literature around LaPt2Si2 is often controversial. In this paper, we clarify the complex evolution of the crystal structure, and the temperature dependence of the development of density wave transitions, in good quality LaPt2Si2 single crystals, with high resolution synchrotron X-ray diffraction data. According to our findings, on cooling from room temperature LaPt2Si2 undergoes a series of subtle structural transitions which can be summarised as follows: second order commensurate tetragonal (P4/nmm)-to-incommensurate structure followed by a first order incommensurate-to-commensurate orthorhombic (Pmmn) transition and then a first order commensurate orthorhombic (Pmmn)-to-commensurate tetragonal (P4/nmm). The structural transitions are accompanied by both incommensurate and commensurate superstructural distortions of the lattice. The observed behavior is compatible with discommensuration of the CDW in this material. 

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321708 (URN)10.48550/arXiv.2211.12617 (DOI)
Note

Published in Communications Materials DOI: 10.1038/s43246-023-00406-y

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2024-02-05Bibliographically approved
11. Q-dependent Phonon Renormalization and Non-Conventional Critical Behavior in the CDW Superconductor LaPt2Si2
Open this publication in new window or tab >>Q-dependent Phonon Renormalization and Non-Conventional Critical Behavior in the CDW Superconductor LaPt2Si2
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(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321710 (URN)
Note

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2023-12-07Bibliographically approved
12. Engineering a pure Dirac regime in ZrTe5
Open this publication in new window or tab >>Engineering a pure Dirac regime in ZrTe5
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(English)In: SciPost Physics, E-ISSN 2542-4653Article in journal (Other academic) Accepted
Abstract [en]

Real-world topological semimetals typically exhibit Dirac and Weyl nodes that coexist with trivial Fermi pockets. This tends to mask the physics of the relativistic quasiparticles. Using the example of ZrTe5, we show that strain provides a powerful tool for in-situ tuning of the band structure such that all trivial pockets are pushed far away from the Fermi energy, but only for a certain range of Van der Waals gaps. Our results naturally reconcile contradicting reports on the presence or absence of additional pockets in ZrTe5, and provide a clear map of where to find a pure three-dimensional Dirac semimetallic phase in the structural parameter space of the material.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-321712 (URN)10.48550/arXiv.2206.13957 (DOI)
Note

QC 20221129

Available from: 2022-11-21 Created: 2022-11-21 Last updated: 2022-11-29Bibliographically approved

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