Journal of Alloys and Compounds 380 (2004) 268–273 Electric and magnetic properties of sol–gel silica powders doped with ferrofluid Ró ˙ za Kornak a,∗ , Krzysztof Maruszewski a,b , Wieslaw Str¸ ek b , Krystyna Haimann a , W. Dudzi´ nski a , Andrzej A. Vogt c , Hubert A. Kolodziej c a Institute of Materials Science and Applied Mechanics, Wroclaw University of Technology, 50-370 Wroclaw, Poland b Institute of Low Temperature and Structure Research, Polish Academy of Science, 50-950 Wroclaw, Poland c Faculty of Chemistry, Universityof Wroclaw, 50-383 Wroclaw, Poland Abstract SiO 2 powders with magnetic properties have been prepared via the sol–gel method. Morphology of the magnetic powders has been investigated by scanning electron microscope (SEM). The magnetic susceptibility and electric permittivity measurements of the obtained materials have been performed by means of the lumped-capacitance method. The complex magnetic permeability measurements have been performed by means of the inductance method using toroidal-shaped samples. © 2004 Elsevier B.V. All rights reserved. Keywords: Sol–gel; Magnetic particles; Magnetic permeability; Electric permittivity 1. Introduction Nanocomposite materials with magnetic particles dis- persed in organic or inorganic matrices are of great interest due to their various applications [1]. Magnetic nanoparticles of a size of a single magnetic domain possess very inter- esting properties and they possess the potential to replace many of the conventional magnetic materials [2,3]. Ferrites (ceramic ferromagnetic materials) have been widely used as magnets, magnetic recording materials as well as cores and wave absorbers because they can operate at high frequencies and are accessible at low prices [4,5]. Nanometer-sized mag- netic materials have attracted attention of many researchers because magnetic nanoparticles exhibit such unusual chem- ical and physical properties as superparamagnetism and quantum tunneling of magnetization [6]. Superparamag- netic nanoparticles also find important medical applications, e.g. magnetic cell sorting, magnetocytolysis, drug-targeting experiments, etc. [7,8]. Nanoparticles can be prepared via dry processes (sputtering and CVD) or by liquid-based pro- cesses (sol–gel or thermal and ultrasonic decomposition of readily decomposable metal compounds) [1]. ∗ Corresponding author. E-mail address: kornak@immt.pwr.wroc.pl (R. Kornak). In this article, we report preparation and characteriza- tion of magnetic nanopowders via the sol–gel method. This approach enables to obtain modified silica powders doped with compounds possessing ferrimagnetic properties. The obtained materials display the broad-band absorption—both the electric permittivity and magnetic permeability. 2. Experimental Silica powders doped with a ferrofluid (called FF21) have been prepared by the sol–gel method. To the best of our knowledge it is the first time when such material has been received by the sol–gel method. The preparation of the ferrofluid—FF21 by Kolodziej et al. is described in [9]. The FF21 is a magnetic liquid containing particles of ferromag- netic complexes composed of Fe 2+ and Fe 3+ dissolved in an organic surfactant. These compounds are molecular mag- nets showing very interesting electromagnetic properties and belong to a new group of the EMC compounds (electro- magnetic compatibility) capable of absorbing electromag- netic energy. The magnetic nanopowders were prepared by hydrolysis and polycondensation of tetraethyl orthosilicate in the systems Si(C 2 H 5 O) 4 /NH 3 /C 2 H 5 OH. The sol–gel synthesis of spherical silica particles with narrow size distri- bution is based on the Stöber method [10]. Briefly, 3.1 cm 3 0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.03.054