FMR and DSC study of maghemite nanoparticles in PMMA polymer matrix J. Typek a, * , N. Guskos a,b , A. Szymczyk a , D. Petridis c a Institute of Physics, Szczecin University of Technology, Al. Piastow 17, 70-310 Szczecin, Poland b Solid State Physics, Department of Physics, University of Athens, Panepistimiopolis, 15 784 Zografos, Athens, Greece c Insitute of Materials Science, NCSR Demokritos, Aghia Paraskevi 15 310 Athens, Greece article info Article history: Available online 11 August 2008 PACS: 65.80.tn 76.30.Fc Keyword: Magnetic properties abstract Nanocomposite samples of poly(methyl methacrylate) (PMMA) polymer with a c-Fe 2 O 3 (maghemite) fil- ler have been synthesised and studied by ferromagnetic resonance (FMR) and differential scanning cal- orimetry (DSC) methods. Two types of samples have been investigated: containing 5 wt%, 10 wt% of a maghemite filler. DSC measurements have revealed an increase in the glass transition temperature T g and a decrease in the heat capacity c p with an increase in the concentration of nanoparticles. A FMR study in the 4–300 K temperature range has shown the presence of an asymmetric spectrum that has been ana- lyzed in terms of two Gaussian-shaped components arising from the assumed magnetic anisotropy of the nanoparticles. The FMR investigation has exposed the temperature range of a superparamagnetic regime (60–290 K) and the blocking temperature of T B  60 K. In that range a shift in the resonance line dH r and the linewidth DH is related by dH r  (DH) n , where n = 2.79 indicates a fair amount of disorder in the maghemite system. An analysis of the FMR spectra in terms of two component lines has shown the importance of the dipole–dipole interaction for higher concentrations of maghemite and for T > 220 K. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction The nanocomposite or organic/inorganic hybrid material, repre- senting a new class of materials, has attracted both academic and industrial interest (e.g. [1]). Polymer nanocomposites have differ- ent properties compared to conventional materials. These altered properties range from improved tensile strength, modulus, heat distortion temperature, to barrier properties, UV resistance, and conductivity. Improvements in the tensile strength, modulus, and heat distortion temperature lead to a widespread speculation that polymer nanocomposites would replace conventionally filled materials on a large scale. An important condition for obtaining a desired material with optimum properties is a good dispersion of nanoparticles in a polymer matrix, i.e. a formation with no aggre- gates. One way to avoid particle aggregation is to modify the surface of particles with polymers or functional groups. Polymer chains, covalently attached to the particles, will separate the particles one from another and stabilize the dispersion. For exam- ple, silica particles modified via grafting have been used in nano- composites and produced materials with a better thermal stability and improved mechanical properties [2,3]. Iron oxides are well known magnetic materials, in particular maghemite, c-Fe 2 O 3 , which crystallises in a cubic spinel structure. In recent years magnetic oxide nanoparticles have attracted partic- ular interest due to their unique magnetic properties arising from a complex interplay between the magnetic response of an individual particle and the multitude of interparticle interactions [4–7]. c-Fe 2 O 3 nanoparticles are widely used in catalysis or in magnetic recording media. Polymer-based iron oxide nanoparticles have been studied by many authors [8–18]. Polymers may serve as excellent matrices for magnetic particles in order to synthesise nanocomposite materials that combine the polymer’s functionality and mechan- ical properties with those of a magnetic filler. Magnetic proper- ties of these systems are studied using magnetometer measurements, 57 Fe Mossbauer spectroscopy and magnetic reso- nance techniques. Experimental work on maghemite nanoparti- cles dispersed in polymeric matrices bearing different surface coatings has stressed the importance of surface effects, indicating that the particle microstructure and the host medium can be a significant factor in determining the magnetic response of these systems [15,19]. In this paper the thermal and magnetic properties of poly- methylmethacrylate (PMMA) polymer samples filled with 5 wt% and 10 wt% maghemite nanoparticles are investigated. The glass transition temperature of samples will be determined and its dependence on the maghemite content will be studied. The mag- netic response of both samples will be investigated in a wide temperature range (4–300 K) and the recorded ferromagnetic res- onance (FMR) spectra will be analyzed in terms of appropriate spectral parameters. 0022-3093/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2008.06.090 * Corresponding author. E-mail address: typjan@ps.pl (J. Typek). Journal of Non-Crystalline Solids 354 (2008) 4256–4261 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol