Size, shape and surface properties in realistic models of magnetic nanocrystals

Magnetic hyperthermia is a promising treatment for brain and prostate cancers due to the localised nature of the treatment compared to chemo or radiotherapy. Brain cancer in particular is difficult to treat with conventional therapies due to the sensitivity of the surrounding tissue with only a 14% survival rate after 10 years in the UK. Magnetic nanoparticles used in magnetic hyperthermia must be biocompatible and provide efficient and reliable heating, yet their physical complexity is limiting progress towards their clinical use. Complexity arises due to the small size of the particles (10-100 nm) leading to a range of physical properties such as surface and bulk atomic defects, finite size and thermal effects, multiple oxide phases and surface functionalization. All of these properties contribute to the overall magnetic properties but are extremely difficult to predict theoretically or with simple model approaches. Previous simulations have considered only simple approaches to the magnetic properties of individual magnetic nanoparticles and give limited insight into the properties of real nanoparticles. Yet there is an urgent need to understand the relative importance of these effects so that experimental effort can be focused on their control and optimisation to accelerate development of this potentially life saving treatment. This proposal will address this challenge by developing a realistic model of magnetic nanoparticles to understand the role of the surface on the particle properties and the resulting magnetization dynamics used to generate heat during magnetic hyperthermia.

The aim of the project is to develop a novel atomic scale magnetic model of magnetite nanocrystals to understand the effects of size, shape and the surface on their equilibrium and dynamic magnetic properties. We will use this information to model and understand how the magnetic particles reverse in an applied magnetic field which is directly related to the amount of heat generated during magnetic hyperthermia. Using atomistic spin dynamics we will be able to simulate the effects of thermal fluctuations at the surface on the effective magnetic properties and their importance in determining the reversal mechanism. The interactions between particles can also play a critical role in the overall magnetic properties, and so we will use our model to simulate the interaction of small clusters of particles with atomic resolution giving new insight into their importance. Finally, we will develop an atomistic model of functional core-shell oxide nanoparticles to determine the optimal magnetic properties for magnetic hyperthermia. The computational methods developed in this project will significantly advance the ability to accurately model magnetic composite materials with wide application in the fields of magnetism and spintronics and made freely available to the community within the open source vampire software package. The results from this project will improve our understanding of the properties of magnetite nanocrystals, guide future research on magnetic hyperthermia and accelerate the development of this critical treatment.

This project will potentially enable a new approach to magnetic nanoparticle design and optimization guided by predictive numerical simulations rather than trial and error driven methods typically used today. This will come from a stepwise improvement in the quality of the models by taking into account the effects of realistic surface properties and by benchmarking them against the latest state-of-the-art experimental measurements. The improvement in the models will enable much better predictions of the nanoparticle properties.

Due to the early stage nature of the research the immediate impacts from the project will be improved knowledge of the properties of ferrite nanoparticles and a new simulation capability for composite structures. However, there is significant potential for wider societal impacts in future through the successful development of magnetic hyperthermia as a cancer therapy or ferrite based nanoparticles for biosensing or targeted drug delivery. The ability to predictively model the properties of particles could enable industrial optimisation for applications, often needed to satisfy multiple quality and design requirements. If successful, this could lead to significant health and quality of life benefits for people in the UK and beyond. Pharmaceutical companies have a strong presence in the UK and if magnetic hyperthermia is developed in the UK it could lead to economic benefits such as job creation and wealth generation.

The novel feature enhancements in this project will contribute to the worldwide competitiveness of the VAMPIRE software package, the leading tool for atomistic spin dynamics simulations. The improved competiveness of these software packages also has wider benefits in improving the attractiveness of the UK for international and EU research funding, providing direct benefits through training and employment of skilled researchers. The VAMPIRE software package is widely used in industrial research laboratories worldwide (Seagate Technology, Western Digital, Samsung Semiconductor, Mitsubishi Research Laboratories), and the novel feature enhancements developed in this project will be of direct benefit to all current and future producers of nanomagnetic devices. Such technologies could lead to reduced energy usage with direct and far reaching benefits for global energy consumption and reduced reliance on fossil fuels.

The post doctoral research assistant funded by the project will develop code in order to achieve the project aims, a highly transferable skill in high demand in the UK. A combination of excellent problem solving skills and the ability to develop high performance computer code will make them attractive to other employment sectors such as software and games development, financial services, and advanced manufacturing.