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Controlled Evolutions between Antiferromagnetism and Spin Glass
https://doi.org/10.15102/0002001020
https://doi.org/10.15102/00020010203ed2e3fd-bc73-4892-82f9-9f49ae120cf5
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DronovaMargaritaFulltext.pdf (20.1 MB)
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DronovaMargaritaExamAbstract.pdf (64 KB)
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| Item type | 学位論文 / Thesis or Dissertation(1) | |||||||
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| PubDate | 2025-12-04 | |||||||
| Title | ||||||||
| Title | 反強磁性とスピングラス間の制御された進化 | |||||||
| Language | ja | |||||||
| Title | ||||||||
| Title | Controlled Evolutions between Antiferromagnetism and Spin Glass | |||||||
| Language | en | |||||||
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| Language | eng | |||||||
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| Subject Scheme | Other | |||||||
| Subject | condensed matter physics | materials science | |||||||
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| Resource Type Identifier | http://purl.org/coar/resource_type/c_db06 | |||||||
| Resource Type | doctoral thesis | |||||||
| Identifier Registration | ||||||||
| Identifier Registration | 10.15102/0002001020 | |||||||
| Identifier Registration Type | JaLC | |||||||
| Access Right | ||||||||
| Access Rights | open access | |||||||
| Access Rights URI | http://purl.org/coar/access_right/c_abf2 | |||||||
| Author |
Dronova, Margarita
× Dronova, Margarita
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| Abstract | ||||||||
| Description Type | Abstract | |||||||
| Description | The control over chemical disorder in crystalline matter can be considered as a tool for developing technologically and fundamentally important materials. For example, the technological importance of disorders is recognized in studies of energy materials and microelectronics. The fundamental importance is also exemplified by the discovery of Fractional Quantum Hall Effect at extremely clean interfaces of single crystals of GaAs. While many magnetic systems exhibit long-range magnetic order, certain combinations of spin type, spin interaction and geometry can create spin frustrations leading to disordered spin states; this contrast between ordered and disordered states is exemplified by antiferromagnetism (AFM) and spin glass (SG). While these two states can originate from the same chemical platform but with different levels of chemical disorder, which can be both intriguing and technically challenging, the realization and understanding of this evolution should provide both new perspectives to materials science and the advancement of measurement technology. In this dissertation I explore the relation between magnetic properties and chemical disorder, using AB2O4 spinel structure, more specifically ZnFe2O4, as the platform. The B-site of the structure accommodates a pyrochlore sublattice consisting of a network of corner-sharing tetrahedra, which can support spin frustration. On the other hand, the real material can be affected by chemical disorders such as site-occupancy mixing due to similarity of cation sizes and off-stoichiometry. ZnFe2O4 spinel has been assigned as a magnetically long-range ordered system. However, neutron diffraction studies in the literature have demonstrated only short-range correlation, which raises speculations about spin frustration and possible spin glass (SG) or spin liquid states in this system. We used a high-temperature solution growth technique and magnetic probes to establish a feedback loop between synthesis parameters and crystal quality. Our methodology allows us to distinguish between off-stoichiometry and site occupancy mixing, and also allows us to control it. We show that, unlike commonly produced low-quality crystals, our stoichiometric ZnFe2O4 crystal demonstrates the longrange AFM ground state with no signature of SG in the clean limit of inversion disorder. Although the pyrochlore lattice has a large degree of freedom for its spins in the unit cell, the AFM structure can be fully refined using neutron elastic diffraction. This unique spin structure is composed of FM and AFM local clusters on individual tetrahedrons, arranged in a checkerboard pattern which is strongly correlated with the lattice being distorted into a breathing pyrochlore structure. With our technical understanding of disorder control, we specifically induce the disorder in the system by replacing Fe3+ on the B-site with nonmagnetic Ga3+ ions in the Zn(Fe,Ga)2O4 spinel, but keep other types of disorder at the minimum. This allows us to create a finely stepped transition from AFM to SG and capture the intermediate states in between. This pathway from AFM to SG allows a clear revelation of the disparity between characteristic temperatures of magnetic heat capacity and magnetic susceptibility, which remains an unresolved issue in the spin glass literature. Using neutron magnetic diffuse scattering of characteristic compositions along the evolution pathway, we can correlate the critical fluctuations and dynamic slowdown with AFM and SG respectively. Furthermore, we reveal a correlation between the onset of spin correlation length and the characteristic temperature of the heat capacity. The onset of short-range correlation in SG thus is similar to that in the long-range AFM order of a thermodynamic phase. Our work thus provides a new perspective into the nature of spin glass in real materials. Advancements of new sciences using real crystalline materials can be greatly dependent on their quality. Successful differentiations can reveal magnetic behavior hidden beneath excessive chemical disorder. In the field of quantum magnetism, differentiating between spin frustration and chemical disorders is likely to be a long-lasting challenge for many subjects, including exotic topics such as quantum spin liquids. The approach to fine tune the type and amount of chemical disorder opens a road for new materials and facilitates the improvement of the characterization techniques. |
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| Language | en | |||||||
| Exam Date | ||||||||
| 2025-10-24 | ||||||||
| Degree Conferral Date | ||||||||
| Date Granted | 2025-11-30 | |||||||
| Degree | ||||||||
| Degree Name | Doctor of Philosophy | |||||||
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| Dissertation Number | 甲第213号 | |||||||
| Degree Conferrral Institution | ||||||||
| Degree Grantor Name Identifier Scheme | kakenhi | |||||||
| Degree Grantor Name Identifier | 38005 | |||||||
| Degree Grantor Name | Okinawa Institute of Science and Technology Graduate University | |||||||
| Version Format | ||||||||
| Version Type | VoR | |||||||
| Version Type Resource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||||
| Copyright Information | ||||||||
| Rights | © 2025 The Author. | |||||||
