Dissertation
Ferrimagnetic organic semi-conductors and lanthanides, a density functional approach
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2023
DOI: 10.25820/etd.006935
Abstract
This work studies a group of magnetic semiconductors, with a major focus on vanadium tetracyanoethylene (V[TCNE]x, x ≈ 2), an organic-based ferri-magnetic with high magnetic order- ing temperature and low loss magnetic dynamics. Magnetic materials like VTCNE are interesting to a number of sub-fields. In spintronics, a high ordering temperature, low loss of energy, as well as ease of depositing and patterning may enable applications in spin-based data transport systems. In quantum information, the coherent magnonic properties and ease of doping due to permanent porosity of VTCNE makes it an interesting candidate for quantum information material as well.
For this work, We perform density functional theory (DFT) calculations in order to lay down a theoretical ground work for said materials. We closely compare our theoretical results with experimental measurements from our collaborators, and have then obtained consistent match between our results and have provided both sides with additional insights into this group of mate- rials. We have looked at the structural ordering, electronic structure, magnetic anisotropy, phonon modes and its implications to ageing, dielectric properties, elastic and magneto-elastic proper- ties of VTCNE. We have also explored different transition-metal-TCNE systems, various gas doped VTCNE systems, and other systems with similar magnetic properties, like vanadium tetra- cyanobenzene (VTCNB) and Prussian blue analogues (PBA). Some thermal properties like coefficient of thermal expansion have also been explored.
We have also worked on the ab initio calculation of crystal field splitting of lanthanide doped materials. We carefully examined methods present in the literature and developed our own code to combine with the DFT calculation and obtain the targeted result. We put our calculated crystal field splittings to test against experimental results and obtained a satisfying match between the results. This work has the potential to be extended to the calculation of new systems and make predictions on their potential as quantum transduction devices.
Details
- Title: Subtitle
- Ferrimagnetic organic semi-conductors and lanthanides, a density functional approach
- Creators
- Yueguang Shi
- Contributors
- Michael E. Flatté (Advisor)Craig E. Pryor (Committee Member)Denis R. Candido (Committee Member)Ezekiel Johnston-Halperin (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Summer 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006935
- Number of pages
- xi, 123 pages
- Copyright
- Copyright 2023 Yueguang Shi
- Language
- English
- Date submitted
- 07/25/2023
- Description illustrations
- illustrations, tables, graphs,
- Description bibliographic
- Includes bibliographical references (pages 99-123).
- Public Abstract (ETD)
- This work studies a class of semiconductors with special magnetic properties that can be utilized to store and transport data, in particular, a unique material called vanadium tetracyanoethy- lene (VTCNE). What makes this material so intriguing is its desirable magnetic properties at room temperature, and low energy loss during such magnetic processes. Thanks to this magnetic prop- erty, VTCNE has potential to be used in data transport devices and quantum computers. To study these materials, we used computer simulation method called the density functional theory (DFT) calculations. Such calculations simulate each atoms in a molecule, and calculate the properties of real-life materials. We also investigated how the properties change when we change to a slightly different molecule, or fill some smaller molecules into the larger VTCNE molecule. By exploring all these, we gained a firmer understanding of not only VTCNE, but also a range of similar materials. In addition, we studied another type of material: those with rare earth metal impurities in them. The impurity have the potential to have powerful implications in quantum devices, but there is a catch: we want its electrons to carry very specific levels of energies. Interestingly, the host material we plant the impurity in can affect such energies, and this effect is called the crystal field splitting. In this work, we explored this effect using DFT calculations, and by studying various different impurities and host materials, we can fine-tune the energies, and potentially discover new materials useful in quantum information.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984454642302771
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