Atomistic simulations of iron oxides

Iron oxides such as magnetite, maghemite and cobalt ferrite are of huge importance to biomedical applications where they are used in cancer treatments and drug delivery. The ability to fine tune their magnetic properties for these applications has seen great interest in recent years. While they have been studied for centuries in bulk form, their properties at the nanoscale have only seen a surface level of understanding. In this thesis, I present a state-of-the-art investigation into the strength and scaling of these materials using an atomistic model to simulate them on a scale comparable to realistic applications. By forming an accurate model of the materials, outlining their structure, exchange interactions and anisotropy, each material is simulated with unprecedented detail, showing the changes in the overall system as the individual atomic spins move. This study shows how finite size effects lower the magnetic properties, such as the Curie temperature and magnetisation scaling of the system depending on the size and shape of the particle. As they are modelled at the atomic scale, the sublattices of each material have been investigated, showing that the overall properties are a symptom of multiple interacting components which can behave differently to each other and scale differently with temperature. In addition to simulating each material on its own, core-shell particles consisting of combinations of each material have also been investigated to better understand the behaviour of each system when the relative sizes of the core and shell are changed, as well as the overall properties of the particle which can be fine tuned for different applications.