Magnetic characterization of Fe nanoparticles dispersed in phyllosilicate type silicon oxide

We present the magnetic properties of silica-supported metal (Fe,catalyst) nanoparticles synthesized by precipitation of metal nitrate in ammonia-based medium. Our goal is the study of possible metal-support interactions in the nanoporous catalyst. The temperature dependence of the magnetization for all samples display spin-glass like behavior below c.a. 11-12 K, with clear Curie-Weiss dependence in the high-temperature regime. Spin-glass-like behavior was inferred from dynamic AC susceptibility data after analyzing the frequency-dependence of the in-phase component χ'(f) by the expression W = T f /[T f =3.0 x 10-3. We found that the magnetic behavior of the catalyst is drastically affected by the existence of interactions between the metal and the support. 1. Introduction Nanosized particles of ferromagnetic metals as Fe, Ni and Co have attracted great interest because of their physical properties and potential applications as catalyst, magnetic recording media and drug delivery systems, etc [1,2]. Numerous physical and chemical methods have been employed to produce metal nanocrystals, including sputtering, grinding, solution phase metal salt reduction, etc. Significant progress has been made in preparing nearly monodisperse metals. Strong magnetic interactions in Ni, Fe and Co particle systems make it difficult to form stable systems. Uncontrolled agglomeration of the magnetic particles often makes it impossible to employ separation procedures which could narrow the size distribution [3,4,]. A favored approach to assemble and maintain metallic nanoparticles is to form nanocomposites whereby the nanoparticles are embedded in a non-magnetic support that provides mechanical and