Magnetic properties characterization of functionalized iron oxide nanoparticles
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1237-TT05-15
Magnetic properties characterization of functionalized iron oxide nanoparticles
Yuan Yuan and Diana-Andra Borca Tasciuc* Mechanical, Aerospace and Nuclear Engineering Department Rensselaer Polytechnic Institute, Troy, NY 12180 U.S.A.
ABSTRACT This paper used complex magnetic susceptibility measurements to investigate the effects of different coatings on the susceptibility of iron oxide nanoparticles. The two coatings used in these measurements were aminosilane and carboxymethyl-dextran. Susceptibility measurements were carried out over a range of frequencies from 10 KHz to 1 MHz using a differential impedance method. The differential impedance measurement setup was validated by measuring the susceptibility of ferrofluids and comparing the results to values previously published in literature. The theoretical relaxation times based on Brownian and Neel mechanisms were used to predict the resonance frequency of imaginary part of complex susceptibility for iron oxide nanoparticles. INTRODUCTION Ferrofluids, which are colloidal suspensions of nanoscale iron oxide particles, have attracted significant interest in recent years for their potential application in cancer hyperthermia[1-3].The magnetic nanoparticles used for hyperthermia applications consist of single magnetic domains, and therefore exhibit superparamagnetic properties[4]. Consequently, the heat generation of magnetic nanoparticles is due to the reorientation of the magnetic dipole, which tends to follow the polarity of the field. This re-orientation can be achieved via two mechanisms: particle rotation (Brownian relaxation); or re-orientation of the magnetic moment inside the particle (Neel relaxation)[5]. Depending on several parameters, such as frequency of the magnetic field, particle size or particle immobilization, one mechanism may dominate, or both can be equally important[6-8]. In principle, for bare superparamagnetic iron oxide nanoparticles, the Neel relaxation occurs at small particle diameters, while for larger particle size Brown relaxation is prevailing[9,10]. However, recent results, show that the heat generation rate of iron oxide nanoparticles can vary widely—even between similar nanoparticle systems [ 11 - 13 ]. These differences in heat generation rate can be attributed to two main factors: nanoparticle clustering and nanoparticle coating[11,14]. Both these phenomena may change the effective magnetic dipole of the particle *
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as well as the relaxation time associated with Neel and Brownian rotation. The relative importance of the two relaxation processes can be assessed by looking at the imaginary part of magnetic susceptibility[10]. For this reasons, it is important to investigate the effect of the coating on the magnetic susceptibility of ferrofluids. In this paper, the complex susceptibility measurement of iron oxide in aminosilane and carboxymethyl-dextran matrix is carried out using a differential impedance method. EXPERIMENTAL SETUP The method used to measure the susceptibility of
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