Simulation, Preparation and Characterisation of Magnetocaloric Thin Films
Lead Research Organisation:
Cardiff University
Department Name: School of Physics and Astronomy
Abstract
This is a joint research programme between School of Physics and School of Engineering, exploiting the synergy of expertise
and facilities between two schools in the area of materials for energy applications. Increasing the energy efficiency of systems
has a noticeable effect on energy footprints. Magnetic refrigeration has recently emerged as a promising technology that
shows huge potential to improve the energy efficiency of modern refrigeration systems. The principle of magnetic
refrigeration is based on the magnetocaloric effect, in which a change in magnetic field induces thermal transport. A thorough
understanding of the magnetocaloric properties of materials has been an important issue in the development of this emerging
technology and is the framework of the proposed research in this PhD project.
The objective of the project is to investigate magnetocaloric properties of GdSiGe and manganite materials in attempts to
gain fundamental insights into the avenues leading to the development of high performance and low-cost magnetocaloric
materials. The project provides the candidate exciting opportunity to tackle a forefront S&T challenge with access to a
number of the state-of-the-art facilities, which are widely used by world class research laboratories in Physics and Materials
Sciences. Magnetocaloric materials will be prepared using a PLD (Pulsed Laser Deposition) system. The magnetocaloric
properties and other physical properties will be investigated using the SQUID (superconducting quantum interference device),
MFM (Magnetic Force Microscope), and Infrascope III (Infrared Microscope), etc. Furthermore, modelling of magnetocaloric
properties will be establishedto support data analysis and interpretation.
and facilities between two schools in the area of materials for energy applications. Increasing the energy efficiency of systems
has a noticeable effect on energy footprints. Magnetic refrigeration has recently emerged as a promising technology that
shows huge potential to improve the energy efficiency of modern refrigeration systems. The principle of magnetic
refrigeration is based on the magnetocaloric effect, in which a change in magnetic field induces thermal transport. A thorough
understanding of the magnetocaloric properties of materials has been an important issue in the development of this emerging
technology and is the framework of the proposed research in this PhD project.
The objective of the project is to investigate magnetocaloric properties of GdSiGe and manganite materials in attempts to
gain fundamental insights into the avenues leading to the development of high performance and low-cost magnetocaloric
materials. The project provides the candidate exciting opportunity to tackle a forefront S&T challenge with access to a
number of the state-of-the-art facilities, which are widely used by world class research laboratories in Physics and Materials
Sciences. Magnetocaloric materials will be prepared using a PLD (Pulsed Laser Deposition) system. The magnetocaloric
properties and other physical properties will be investigated using the SQUID (superconducting quantum interference device),
MFM (Magnetic Force Microscope), and Infrascope III (Infrared Microscope), etc. Furthermore, modelling of magnetocaloric
properties will be establishedto support data analysis and interpretation.
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509449/1 | 01/10/2016 | 30/09/2021 | |||
| 1749940 | Studentship | EP/N509449/1 | 30/06/2016 | 31/12/2019 | Alex Evans |
| Description | Magnetocaloric materials are those which undergo a structural and magnetic change at the same critical temperature. The majority of research has focused on bulk samples for their application to solid state refrigeration, we have instead looked into growing these materials as thin films as there has been little research in this area. We have focused on two materials, Gadolinium Silicon Germanium (GdSiGe) and Lanthanum Iron Silicon (LaFeSi), both have been grown on a range on substrates at varying temperatures, pressures and laser fluencies to try to optimise these parameters to maximise the entropy change, a measure of merit in magnetocalorics. These materials have been chosen as they go through a first order phase transition where the magnetic and structural changes are coupled to each other and go through a sudden, discontinuous change with a level of hysteresis. Although GdSiGe has been successfully grown as a thin film previously, our growth techniques forms samples an order of magnitude thinner with a wide range of parameters for optimisation. Preliminary results show thin film growth can be used to increase the critical temperature of GdSiGe. There have also been attempts by other groups to grow LaFeSi as a thin film previously that proved unsuccessful, we have successfully grown samples and have preliminary data showing a relationship between growth temperature and the nature of the phase change, the initial data shows a more complex map of growth temperature and magnetism than that of GdSiGe. Further understanding is being sought through planned polarised neutron reflectometry measurements, which can be used to understand magnetism and structure in thin films with nanometer resolution. The Ising model (which is a cellular automata model using a grid of sites given a nominal value and then allowed to interact with nearest neighbours) has been expanded upon so that it can be more easily applied to magnetocaloric materials. By calculating the strength of interaction between rare earth sites and calculating internal energies of various crystal structures a model has been developed which can mimic results found experimentally for GdSiGe and can be used to computationally investigate stress and strain relationships in such materials. We have also used these models to investigate first order transitions, while most previous work has looked at second order magnetocaloric materials, thus neglecting to compare internal energies from different structures. This potentially offers a new avenue for computational physicists to investigate first order magnetocalorics and first order transitions more generally. |
| Exploitation Route | Academically, as the critical temperature has been seen to increase due to the nature of thin film growth, further investigation into the effects of size and/or stress should be conducted to understand what is causing this increase and to see if it can be fine-tuned to be more applicable to industries. The Ising style model that has been developed has been used to investigate Gadolinium Silicon Germanium (GdSiGe) specifically, but it is generic enough to be used for a wide range of other magnetocalorics which have not been modelled in this way due to their first order nature. Non-academically, we have focused on the GdSiGe and lanthanum Iron Silicon (LaFeSi) phase change nature on various substrates and controlled using large magnetic fields. Investigation into integration would entail looking at these materials with current driven transitions, removing the need to apply large magnetic fields. Also integration would require studying how the materials interact with components already used in various solid state devices. |
| Sectors | Electronics,Energy,Environment |