Abstract
Magnetic nanoparticles are of great interest for a variety of applications, ranging from medical diagnosis and treatment to information storage and genetic engineering. Their key property is that their magnetization can be manipulated with external magnetic fields. Here researchers study the influence of the spatial orientation of an ensemble of immobilized nanoparticles, with magnetic easy axes aligned parallel with respect to a dynamic external magnetic excitation field, on the magnetization response of the nanoparticles. The authors present a method and experimental proof of concept for estimating the spatial orientation of the easy axis from the magnetization response.
Highlights
Advances in micromachinery and nanotechnology, such as magnetically actuated microrobots for navigating in viscous environments, are important driving forces in medicine
It has been shown that the spatial orientation of an ensemble of immobilized nanoparticles with parallel-aligned magnetic easy axes has an effect on the magnetization response to an external dynamic magnetic field
For nanoparticles with parallel alignment of the easy axes, the orientation of the easy axes with respect to the magnetic excitation field is one of the key parameters for their magnetization response [7] for large degrees of parallel alignment [8]. We use this dependency to estimate the spatial orientation of the easy axes relative to an external magnetic excitation field from the magnetization response of the nanoparticles
Summary
Advances in micromachinery and nanotechnology, such as magnetically actuated microrobots for navigating in viscous environments, are important driving forces in medicine. We use this dependency to estimate the spatial orientation of the easy axes relative to an external magnetic excitation field from the magnetization response of the nanoparticles. Application-wise, we use these findings to perform a data-driven estimation method for the spatial orientation of the easy axis of magnetic nanoparticles and provide a proof of principle in a magneticparticle-imaging [10,11] setting where the orientation can be estimated tomographically In this context, the proposed method provides an additional image contrast, such as the recently introduced temperature [12], viscosity [13,14], and core-size [15] contrasts, all of which are provided in addition to the spatial nanoparticle distribution. For immobilized nanoparticles, Brownian rotation is suppressed and only the Néel rotation derived from the phenomenological Landau-LifshitzGilbert equation remains [19,20]
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