Dynamics of interacting magnetic nanoparticles: effective behavior from competition between Brownian and Néel relaxation

Abstract

The intriguing properties of magnetic nanoparticles have sparked a growing number of theoretical studies as well as practical applications. Here, we provide the first comprehensive study of the influence of...

Comparative Modeling of Frequency Mixing Measurements of Magnetic Nanoparticles Using Micromagnetic Simulations and Langevin Theory

“…Another reason could be that MNPs form clusters of a few particles in the experimental setting, which Dennis et al consistently found for nanomag-D SPIO from small-angle neutron scattering (SANS) and transmission electron microscopy [ 37 ]. Clustering of MNPs has been suggested to lead to increased particle–particle interaction, changed effective anisotropy, and restriction of MNP rotatability [ 38 , 39 , 40 ]. Although the interplay of these clustering effects on MNP relaxation behavior is the subject of ongoing discussions [ 39 , 40 , 41 , 42 ], it is overall assumed to diminish the experimental signal intensity [ 43 ].…”

“…Clustering of MNPs has been suggested to lead to increased particle–particle interaction, changed effective anisotropy, and restriction of MNP rotatability [ 38 , 39 , 40 ]. Although the interplay of these clustering effects on MNP relaxation behavior is the subject of ongoing discussions [ 39 , 40 , 41 , 42 ], it is overall assumed to diminish the experimental signal intensity [ 43 ]. Both the rise of particle–particle interaction—although purposefully excluded from this study—and the influence of varying could be investigated in future MC-simulations studies (e.g., by diffusion-limited colloidal aggregation [ 42 ]) to advance the understanding of its influence on mixed frequency excitation signal generation.…”

Enhancement of Neel Relaxation at Magnetic Heating Performance of Iron Oxide Nanoparticles 

“…SAR value can be defined by absorbed/converted magnetic energy into thermal energy [Fortin, 2008]. Brownian relaxation is mainly effective for magnetic nanoparticles suspended in a viscous liquid, which permit the nanoparticles rotate freely [Ilg, 2020]. On the other hand, Neel relaxation occurs by Eddy currents on the particle surface [Hergt, 2009].…”

“…The magneto heating originating from two basic mechanisms, which govern the magnetization relaxation of magnetic nanoparticles. The internal magnetization relaxation and the rotational diffusion of whole magnetic nanoparticles are defined Néel relaxation and Brownian relaxation, respectivley [Ilg, 2020]. The mechanism of magneto-heating is expected to be mainly depended on both mechanisms of Neel relaxation and Brownian relaxation [Celik, 2014;Ilg, 2020].…”

“…The internal magnetization relaxation and the rotational diffusion of whole magnetic nanoparticles are defined Néel relaxation and Brownian relaxation, respectivley [Ilg, 2020]. The mechanism of magneto-heating is expected to be mainly depended on both mechanisms of Neel relaxation and Brownian relaxation [Celik, 2014;Ilg, 2020]. Both relaxations cause an increase in temperature, however for hypertermia applications Neel Relaxation has specific advantages, especially high specific absorption rate (SAR) value, according to the Brownain relaxation due to highly dependent on viscosity of surronded enviourment of particles [Fortin, 2008].…”