Dynamic single-domain particle model for magnetite particles with combined crystalline and shape anisotropy
Dynamic single-domain particle model for magnetite particles with combined crystalline and shape anisotropy
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DOI：
10.1088/0022-3727/48/27/275001
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发表时间：
2015-07-15
影响因子：
3.4
通讯作者：
Buzug, T. M.
中科院分区：
文献类型：
--
作者：
Graeser, M.;Bente, K.;Buzug, T. M.
超顺磁性氧化铁纳米粒子（SPION）的动力学行为尚未完全了解。在磁粒子成像（MPI）中，SPION用于确定示踪材料分布的定量实时医学图像。为了达到亚毫米范围的空间分辨率，MPI需要一个设计良好的仪器，提供超过2 T m（-1）的磁场梯度。然而，由于粒子性能强烈影响成像过程的灵敏度，因此粒子参数的优化是一个关键因素，这并不容易解决。今天大多数MPI的模拟使用朗之万模型来描述粒子的行为。在平衡状态下，模型与测量数据相匹配。如果施加中kHz频率范围内的交变场，则颗粒的动态行为由于各向异性效应、颗粒-颗粒相互作用和/或在多核颗粒的情况下的交换相互作用而不同于朗之万理论。本文在前人工作的基础上提出了一个模型，该模型考虑了固定化单畴单核粒子的晶体和形状各向异性。该模型适用于典型的MPI频率和场强与不同的可能叠加的各向异性效应，导致粒子响应的差异。它示出，尽管相对较高的各向异性常数，磁晶各向异性能不淬火MPI的信号响应。形状和晶体各向异性的建设性叠加导致在相关成像模态的灵敏度和分辨率方面的最佳性能，并且与单一形状各向异性相比略微降低了能量势垒。
The dynamical behaviour of superparamagnetic iron oxide nanoparticles (SPIONs) is not yet fully understood. In magnetic particle imaging (MPI) SPIONs are used to determine quantitative real-time medical images of a tracer material distribution. For reaching spatial resolution in the sub-millimetre range, MPI requires a well engineered instrumentation providing a magnetic field gradient exceeding 2 T m(-1). However, as the particle performance strongly affects the sensitivity of the imaging process, optimization of the particle parameters is a crucial factor, which is not easy to address. Today most simulations of MPI use the Langevin model to describe the particle behaviour. In equilibrium, the model matches the measured data. If alternating fields in the mid kHz frequency range are applied, the dynamic behaviour of the particles differs from the Langevin theory due to anisotropy effects, particle-particle-interactions and/or exchange interaction in case of multi-core particles. In this paper a model based on previous work is introduced, which was adopted to include crystal and shape anisotropy of immobilised mono-domain single-core particles. The model is applied to typical MPI frequencies and field strengths with different possible superposition of the anisotropy effects, leading to differences in the particle response. It is shown that, despite comparatively high anisotropy constants, the magnetocrystalline anisotropy energy does not quench the signal response for MPI. The constructive superposition of shape and crystal anisotropy leads to the best performance in terms of sensitivity and resolution of the associated imaging modality and slightly reduces the energy barriers compared to a sole-shape anisotropy.