Alternating magnetic field energy absorption in the dispersion of iron oxide nanoparticles in a viscous medium Ilona S. Smolkova a,b , Natalia E. Kazantseva a,n , Vladimir Babayan a , Petr Smolka a , Harshida Parmar a , Jarmila Vilcakova a , Oldrich Schneeweiss c , Nadezda Pizurova c a Centre of Polymer Systems, University Institute, Tomas Bata University in Zlin, nad Ovcirnou 3685, 760 01 Zlin, Czech Republic b Polymer Centre, Faculty of Technology, Tomas Bata University in Zlin, T.G. Masaryk Sq. 275, 762 72 Zlin, Czech Republic c Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, 616 62 Brno, Czech Republic article info Article history: Received 3 April 2014 Received in revised form 13 August 2014 Available online 6 September 2014 Keywords: Iron oxide nanoparticles Coprecipitation Magnetic interactions Specific loss power Hyperthermia abstract Magnetic iron oxide nanoparticles were obtained by a coprecipitation method in a controlled growth process leading to the formation of uniform highly crystalline nanoparticles with average size of 13 nm, which corresponds to the superparamagnetic state. Nanoparticles obtained are a mixture of single-phase nanoparticles of magnetite and maghemite as well as nanoparticles of non-stoichiometric magnetite. The subsequent annealing of nanoparticles at 300 1C in air during 6 h leads to the full transformation to maghemite. It results in reduced value of the saturation magnetization (from 56 emu g 1 to 48 emu g 1 ) but does not affect the heating ability of nanoparticles. A 2–7 wt% dispersion of as-prepared and annealed nanoparticles in glycerol provides high heating rate in alternating magnetic fields allowed for application in magnetic hyperthermia; however the value of specific loss power does not exceed 30 W g 1 . This feature of heat output is explained by the combined effect of magnetic interparticle interactions and the properties of the carrier medium. Nanoparticles coalesce during the synthesis and form aggregates showing ferromagnetic-like behavior with magnetization hysteresis, distinct sextets on Mössbauer spectrum, blocking temperature well about room temperature, which accounts for the higher energy barrier for magnetization reversal. At the same time, low specific heat capacity of glycerol intensifies heat transfer in the magnetic dispersion. However, high viscosity of glycerol limits the specific loss power value, since predominantly the Neel relaxation accounts for the absorption of AC magnetic field energy. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Nowadays there are four main concepts of using magnetic iron oxide nanoparticles (NPs), magnetite and maghemite, in medicine: cell separation, imaging, drug delivering, and heating [1–6]. All of these approaches require definite magneto-structural properties of NPs. As an example, there are several commercially available iron oxide formulations for Magnetic Resonance Imaging; however, owing to their superparamagnetic (SPM) behavior and low heating potential in alternating (AC) magnetic fields in a frequency range of hundreds of kHz and amplitudes below 15 kA m –1 , they are not suitable for magnetic hyperthermia (MH). In MH, the ability of a magnetic material (usually a dispersion of magnetic particles in a carrier medium) to dissipate the energy of an AC magnetic field is evaluated by specific loss power (SLP). There are strict limits on the frequency (0.05 rf r1.5 MHz) and the amplitude (H r15 kA m 1 ) of the applied AC magnetic field in MH due to physiological restrictions [7]. In this range of field parameters, SLP is defined as [8] SLP ¼ πμ 0 χ″fH 2 =ρ; ð1Þ where μ 0 is the permeability of vacuum, f is the frequency and H is the amplitude of AC magnetic field, χ″ is the imaginary part of susceptibility, and ρ is the mass density of the magnetic material. Thus, once the parameters of the AC magnetic field are specified for MH, the properties of the magnetic particles must be optimized for the AC magnetic field applied [9,10]. Moreover, it has been shown in [9,11] that the SLP is determined not only by the above-mentioned parameters, but also by the viscosity of the carrier medium. The total absorption of AC magnetic field energy is determined by two dissipation mechanisms: the intrinsic magnetic dynamics of magnetic moment (Neel relaxation) and the external rotational dynamics of the particle (Brown relaxation) with characteristic Neel Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2014.08.096 0304-8853/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ420 57 603 8114; fax: þ420 57 603 1444. E-mail address: nekazan@yahoo.com (N.E. Kazantseva). Journal of Magnetism and Magnetic Materials 374 (2015) 508–515