Magnetic particle hyperthermia: Néel relaxation in magnetic nanoparticles under circularly polarized field

Abstract

The mechanism of magnetization reversal in single-domain ferromagnetic particles is of interest in many applications, in most of which losses must be minimized. In cancer therapy by hyperthermia the opposite requirement prevails: the specific loss power should be maximized. Of the mechanisms of dissipation, here we study the effect of Néel relaxation on magnetic nanoparticles unable to move or rotate and compare the losses in linearly and circularly polarized fields. We present exact analytical solutions of the Landau-Lifshitz equation as derived from the Gilbert equation and use the calculated time-dependent magnetizations to find the energy loss per cycle. In frequencies lower than the Larmor frequency, linear polarization is found to be the better source of heat power, at high frequencies (beyond the Larmor frequency) circular polarization is preferable.

Magnetic particle hyperthermia: Power losses under circularly polarized field in anisotropic nanoparticles

“…(1)] has the simplest form: a time-independent magnetization vector [10][11][12]. The transformation is done by an appropriate rotation [10]:…”

“…(25) in Ref. [10]] (in the case of the repulsive fixed point u x0 and u z0 having been multiplied by −1). The attractive fixed point of the LLG equation in the rotating frame corresponds to the stable steady-state solution obtained in the laboratory frame [Eq.…”

“…Indeed, in the case of the linearly polarized applied field, the optimization of energy loss with respect to the amplitude and frequency of the external field has been studied in detail [4,8,9]. It is natural to ask what is the dependence of the specific absorption rate on the nature of polarization, i.e., whether a better heating efficiency can be achieved by a circularly polarized applied field [5][6][7]10]. The study of dynamical effects of a circularly polarized field has received considerable attention [11][12][13][14][15].…”

“…[10] when no thermal effects were included. In the low-frequency limit, the energy loss per cycle was found to be larger in the case of the linearly polarized applied field as compared to the circularly polarized one.…”

Efficient DNA release from PAMAM dendrimer-modified superparamagnetic nanoparticles for DNA recovery

“…21,22 Because the heat is generated from the MNP core, the energy should be directly transferred to the water and other molecules that exist locally on the MNP surface, resulting in the rapid and efficient heating of the target molecule. In this study, we used an AMF to enhance DNA release from the PAMAM-SpMNP surface.…”