Dissertation/ Thesis
Neutron Scattering Study of Ni-V and Ce(Ni,Cu)Sn Close to the Onset of Magnetic Order.
| العنوان: | Neutron Scattering Study of Ni-V and Ce(Ni,Cu)Sn Close to the Onset of Magnetic Order. |
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| المؤلفون: | Bhattarai, Shiva |
| بيانات النشر: | Kent State University / OhioLINK, 2022. |
| سنة النشر: | 2022 |
| المجموعة: | Ohiolink ETDs |
| Original Material: | http://rave.ohiolink.edu/etdc/view?acc_num=kent1667922471030508 |
| مصطلحات موضوعية: | Condensed Matter Physics, quantum phase transition, disorder, magnetic clusters, quantum Griffiths phase, neutron scattering, inelastic neutron scattering, polarized small angle neutron scattering, Kondo insulator, magnetic correlation length, magnetic fluctuations |
| الوصف: | Strongly correlated electron systems are at the borderline of competing phases andcan be tuned through different ground states by slight modifications. Therefore, theyare good examples to study a quantum phase transition (QPT), to reveal how a quantum critical point (QCP) at zero temperature is responsible for the unconventionalproperties observed at finite temperatures. QPTs are zero-temperature phase transitions, they are more complex and less understood than common phase transitionsat finite temperatures. Examples are lacking, especially in the case where disorder isinvolved. Recent theories predict the possibility of an exotic quantum critical pointin itinerant magnets with induced disorder that is accompanied by a quantum Grif-fiths phase. To explore such unconventional properties in close neighborhood to amagnetic phase, we aim to reveal the relevant quantum critical fluctuations withneutron scattering. We select systems with different magnetic order and choose astuning parameter chemical substitution to study the effect of disorder. Such experimental study aims to find key elements of a QCP with disorder. The two systemsare the ferromagnetic (FM) alloy, Ni-V, tuned by the V-concentration into a paramagnetic phase, and the non-magnetic Kondo semimetal, Ce(Cu,Ni)Sn, tuned byCu concentration into an antiferromagnetic state. We apply different neutron scat-tering techniques and simple models to get essential characteristics of the magneticcorrelations and fluctuations close to the QCP.Ni-V is a simple FM-alloy with a random atomic distribution that undergoes aquantum phase transition from a ferromagnetic to a paramagnetic state with sufficientsubstitution of Ni by V. First indication of a quantum Griffiths phase came frommagnetization and μSR data, but the scale of the magnetic clusters remained elusive.Optimized small angle neutron scattering (SANS) data on different polycrystalline Ni-V samples close to the QCP finally show a small magnetic scattering response withinthe FM state. Using full polarization analysis, we discover short-range correlationsof order of several nanometers. In addition, the polarized SANS data show evidenceof long-range order. The coexistence of magnetic clusters and long-range ordereddomains explain the unusual properties of this disordered FM with a QCP. Theseresults agree with the expectations of a disordered QCP with a quantum Griffithphase.The non-magnetic anisotropic Kondo insulator, CeNiSn, presents a rather uniquemagnetic excitation spectrum with gaps. Cu doping leads toan antiferromagnetic ordered state with a small magnetic moment. We collectedthe first inelastic neutron scattering data of a single crystalline sample with Cuconcentration at the onset of the magnetic order and revealed the magnetic excitationspectrum at a specific wave vector. It does not show a gap anymore, but magneticorder. In addition, we identify a fluctuation spectrum, including one-dimensionalcritical magnetic fluctuations. These first data already shed some light on the complexbehavior of this Kondo semimetal driven by anisotropic hybridization and disorder.Overall these neutron scattering data reveal relevant quantum fluctuations closeto onset of magnetic order that help to characterize the nature of the transition |
| Original Identifier: | oai:etd.ohiolink.edu:kent1667922471030508 |
| نوع الوثيقة: | Text |
| اللغة: | English |
| الاتاحة: | http://rave.ohiolink.edu/etdc/view?acc_num=kent1667922471030508 |
| Rights: | unrestricted This thesis or dissertation is protected by copyright: some rights reserved. It is licensed for use under a Creative Commons license. Specific terms and permissions are available from this document's record in the OhioLINK ETD Center. |
| رقم الانضمام: | edsndl.OhioLink.oai.etd.ohiolink.edu.kent1667922471030508 |
| قاعدة البيانات: | Networked Digital Library of Theses & Dissertations |
| الوصف غير متاح. |