Evans, Alex
2021.
Simulation, preparation and characterisation of magnetocaloric thin films.
PhD Thesis,
Cardiff University.
Item availability restricted. |
Preview |
PDF
- Accepted Post-Print Version
Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (59MB) | Preview |
PDF (Cardiff University Electronic Publication Form)
- Supplemental Material
Restricted to Repository staff only Download (309kB) |
Abstract
Heisenberg and related models have previously been developed to investigate the magnetocaloric effect. Here an Ising model was developed to simulate the GdSiGe crystal system and used to compare the two dominant phases, monoclinic and orthorhombic, to show a dependence on the inter slab bonding that is present in the orthorhombic phase but not the monoclinic phase and the Tc. The model uniquely utilises 2 Ising models, representing each phase, to compare internal energies and derive a first-order phase change point. The Monte Carlo (MC) method with consideration for only nearest neighbour sites, magnetic coupling strength (J) calculated using the Ruderman-Kittel-Kasuya-Yosida (RKKY) model and an external field H was applied. The cohesive energy, under the assumption of the nearly free electron, was used to show indistinguishability in favour of individual phases. This indistinguishability leads to a first-order coupled magnetic and structural transition over a second-order magnetic transition usually expected from Ising models. Thin-film Magnetocaloric GdSiGe and LaFeCoSi were grown on SiO2 and AlN, SQUID and VSM magnetometry are used to investigate the phase transition and Curie temperature. X-ray, polarised neutron re ectometry and AFM measurements are used to investigate the structural and surface characteristics. For both materials, there exists a distinct change compared to their bulk counterpart. The Curie temperature of both materials moved from the bulk counterparts, with LaFeCoSi having an 8 K lower Tc and GdSiGe an up to 13 K higher Tc. A maximum entropy change for GdSiGe thin film was found to be 0:45 JkgK
Item Type: | Thesis (PhD) |
---|---|
Date Type: | Completion |
Status: | Unpublished |
Schools: | Physics and Astronomy |
Subjects: | Q Science > QC Physics |
Uncontrolled Keywords: | Magnetocaloric, Ising, Phase Transition, Thin Film, FOPT |
Funders: | EPSRC |
Date of First Compliant Deposit: | 23 June 2022 |
Last Modified: | 04 Jan 2023 02:23 |
URI: | https://orca.cardiff.ac.uk/id/eprint/150731 |
Actions (repository staff only)
Edit Item |