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

与化疗或放射治疗相比，磁热疗是治疗脑癌和前列腺癌的一种有前途的局部治疗方法。尤其是脑癌，由于周围组织的敏感性，传统疗法很难治疗，在英国，10年后的存活率只有14%。用于磁热疗法的磁性纳米颗粒必须是生物相容的，并提供有效和可靠的加热，但其复杂的物理特性限制了其临床应用的进展。由于颗粒尺寸很小(10-100 nm)，导致了一系列的物理性质，如表面和体原子缺陷、有限尺寸和热效应、多个氧化物相和表面官能化。所有这些性质都对总体磁性有贡献，但从理论上或用简单的模型方法都很难预测。以前的模拟只考虑了简单的方法来研究单个磁性纳米颗粒的磁性，对真实纳米颗粒的性质的洞察有限。然而，迫切需要了解这些影响的相对重要性，以便实验工作可以集中在它们的控制和优化上，以加速这种潜在的挽救生命的治疗方法的开发。这项提议将通过开发一个现实的磁性纳米颗粒模型来解决这一挑战，以了解表面对颗粒性质的作用以及在磁热治疗过程中用于产生热的磁化动力学。该项目的目的是建立一个新的磁铁矿纳米晶的原子尺度磁模型，以了解尺寸、形状和表面对其平衡和动态磁性能的影响。我们将利用这些信息来模拟和理解磁性粒子在外加磁场中如何反转，磁场与磁热疗过程中产生的热量直接相关。利用原子自旋动力学，我们将能够模拟表面热涨落对有效磁性质的影响，以及它们在确定反转机制中的重要性。粒子之间的相互作用也可以在整体磁性中发挥关键作用，因此我们将使用我们的模型来模拟具有原子分辨率的小粒子团簇的相互作用，从而对它们的重要性有新的认识。最后，我们将开发一个功能核壳氧化物纳米粒子的原子模型，以确定磁热疗的最佳磁性能。在这个项目中开发的计算方法将大大提高准确模拟磁性复合材料的能力，在磁性和自旋电子学领域得到广泛应用，并通过开放源码吸血鬼软件包免费提供给社区。本项目的研究结果将加深我们对磁铁矿纳米晶性质的理解，指导未来的磁热疗研究，并加速这一关键治疗的发展。

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.