Magnon and phonon thermal transport in oxides

Waste heat management and recovery and discovering energy-efficient devices are important problems that we need to solve. To solve these problems, one of the important thing that we need to understand is the thermal transport that happens inside the material. In my PhD work, I advanced the understanding of the mechanism of magnon and phonon thermal transport in oxides. In these studies, I use ultrafast pump-probe metrology, time-domain thermoreflectance to measure the thermal conductivity. The first subject is the relationship between magnons and phonons in low-dimensional quantum magnets, cuprates, which have high magnon thermal conductivity even at room temperature. At high temperatures, I observed that the cuprates still have large magnon contribution to its thermal conductivity even at temperatures larger than the bulk Neel temperature. In addition, the crystals with different spin structures have different temperature dependences. The second topic is on yttrium-iron-garnet, where I hope to understand the magnon-phonon thermal transport inside the YIG crystal, and also to understand the electron-magnon transport across metal-YIG interfaces. In particular, I would like to see how different deposition techniques can affect the thermal conductivity of YIG thin films. Knowing the thermal conductivity is important because YIG thin films are used for spin-Seebeck (SSE) applications, and thermal gradient is important in SSE application. I found that these thin films have lower thermal conductivities compared to the bulk YIG crystal and that GGG thermal conductivities are also lower than what were reported in the literature. In the third topic, I would like to understand the phonon transport inside (SrTiO3)nSrO (n=1-5 and 10) superlattice thin films. Superlattices have been an interest of many studies because of its potential application for energy-harvesting devices, such as thermoelectric devices. I would like to understand better if there is any coherent-incoherent phonon transport transition, like what was observed in graphene superlattice, or AlAs/GaAs superlattice or other oxide perovskites. In addition, I also measured the thermal conductivity of films with various interface density, but no observable incoherent-coherent phonon transition was observed. Finally, I was able to map the thermal conductivity of SiC ceramic matrix composite (CMC) using TDTR. SiC composite has been a subject of study interest because of its potential application for nuclear fuel cladding. However, existing models only used the effective thermal conductivity or only assumed that the thermal property of each material, such as matrix, fiber, and interphase, to stay the same before and after their incorporation into the composite. In this study, I reported the thermal conductivity of each constituent and their temperature dependences. The matrix has varying thermal conductivity from 50 to 120 W/m-K, and it is approximately dependent on 1/T1/2. The fiber has a uniform thermal conductivity of 22 W/m-K, and it is relatively independent of temperature.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Pek, Ella Kartika Putihprayogi

Contributors dc:contributor

• Cahill, David G
• Cooper, S. Lance
• Schleife, Andre
• Krogstad, Jessica

• Thermal Mapping
• Cuprates
• Thermal Transport
• Phonon
• Magnon
• YIG
• SiC composite
• Epitaxial Thin Film

Statement dc:rights

• Copyright 2019 Ella Kartika Putihprayogi Pek

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/106488

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/106488