Journal of Magnetism and Magnetic Materials 289 (2005) 13–16 Preparation of magnetic nanoparticles with large specific loss power for heating applications Robert Mu¨ller à , Rudolf Hergt, Matthias Zeisberger, Wolfgang Gawalek Institut fu¨r Physikalische Hochtechnologie e.V., Albert-Einstein-Str. 9, 07745 Jena, Germany Available online 24 November 2004 Abstract Glass crystallisation method is used as a relatively new technique for the preparation of nanocrystalline magnetic iron oxide. Properties of glassy flakes, the precursor state, prepared powders as well as a water-based ferrofluid were analysed by XRD, TEM and magnetic methods. Different contributions to specific loss power (SLP) are measured by AC-susceptometry, hysteresis loops and a calorimetric method. Values of SLP in the order of 100W/g maghemite may be achieved with the option of further increase by improving the core size distribution. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Tt; 75.50.Mm; 75.40.Gb; 75.60.Jk; 75.60.Lr; 87.54.Br Keywords: Magnetic nanoparticle; Glass crystallisation; Ferrofluids; Ne´el relaxation; Magnetic losses; Magnetic hyperthermia 1. Introduction Magnetic fluids may undergo considerable heating if subjected to AC-magnetic fields. The heating effects being due to different magnetic loss types may be useful for technical heating processes as well as for application in magnetic particle hyperthermia proposed as a tumour therapy. Although principles of hyperthermia using magnetic particles are already known for nearly half a century [1], first therapy runs with human patients were carried out only now [2]. There, magnetic nanoparticles are deposited in tumour tissue and are heated in an alternating magnetic field in order to destroy the tumour. Enhancement of the specific loss power (SLP) of magnetic AC-losses of nanoparticles would allow a reduction of the tissue load with magnetic material and improve the reliability of therapy. During remagnetisa- tion of magnetic nanoparticles in an AC-field several types of loss processes (hysteresis losses, Ne´el or Brown relaxation) may appear which depend strongly on the mean particle size (for a review see Refs. [3,4]). It was shown recently that the size distribution width of nanoparticles has crucial influence on the frequency dependence of SLP [5,6]. Several types of magnetite or maghemite which, at present, are the only magnetic materials being accepted for medical applications were investigated with respect to SLP [5–7]. In the present paper the glass crystallisation technique (GCT) is investigated with respect to preparation of nanoparticles with improved SLP. Glass crystallisation method which is well known for Ba-hexaferrite preparation [8] was only recently used for the preparation of nanocrystalline magnetite/maghemite powders [9] by solving the special problem of avoidance of non-magnetic iron oxides or other non-magnetic phases. The particles grow during a temperature treatment isolated in a glass matrix and the mean particle size can be easily controlled by the temperature treatment (in contrast to the size of ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.11.005 à Corresponding author. Tel.: +493641206109; fax: +493641206199. E-mail address: robert.mueller@ipht-jena.de (R. Mu¨ller).