Iron Nanoparticles Embedded in Silica Glass: A Computational Study
- PDF / 523,227 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 84 Downloads / 251 Views
0959-M12-03
Iron Nanoparticles Embedded in Silica Glass: A Computational Study Peter Kroll, Jens Theuerkauf, and Thomas Wieland Inorganic Chemistry, RWTH Aachen, Landoltweg 1, Aachen, 52056, Germany
ABSTRACT We performed electronic structure calculations within density functional theory including ab initio molecular dynamic simulations of isolated Fe13 and Fe55 clusters. We observed the energy preference of icosahedral over cuboctahedral clusters for both Fe13 and Fe55. The magnetic structure is ferromagnetic for Fe13 clusters, but anti-ferromagnetic for Fe55 clusters. The isolated clusters exhibit a HOMO-LUMO gap. Subsequently, we modeled the embedding of Fe13 and Fe55 clusters in silica glass, creating several models of different size. All models show a homogeneous trend after optimization, however. For embedded clusters we observed the formation of an iron oxide interface between the cluster and the dielectric matrix. The magnetization of the embedded clusters is slightly larger than the magnetization of free clusters. The small clusters retain their electronic structure around the Fermi-level, still exhibiting a HOMO-LUMO gap, despite some major geometrical distortions of the clusters. INTRODUCTION Nanostructured materials can provide unique properties as quantum effects in the nanometer regime lead to many physical and chemical properties showing strong size dependence. In search of new magnetic materials fitting the needs in ultrahigh-density magnetic storage devices the investigation of nanoparticles is not only very fascinating but also of utmost technological importance. A detailed understanding of the properties of magnetic nanoparticle, therefore, is inevitable to elucidate the prospects for materials applications. Experimental information about transition metal nanoparticles, free clusters or embedded particles, is still very limited. For example, the geometries of free iron, cobalt, or nickel clusters containing more than 13 atoms are not known. Metal clusters embedded in an insulating host were among the first nanocomposite systems to be formed by ion implantation [1]. Some nano-composites exhibit pronounced optical effects, including absorption due to surface-plasmon resonance and a strong third-order nonlinear optical susceptibility. A chemical route towards such materials is the sol-gel approach. It provides an alternative path to pure metal as well as metal oxide nanoparticles embedded in a silica matrix. The size distribution of the particles can be tailored to some extend and kept very narrow [2]. Enhanced catalytic, magnetic, electronic, and optical properties are the driving force for research in this area.
Computational studies can provide some insight in structure and properties of magnetic clusters. Availability of state-of-the-art accurate and efficient numerical methods of density functional theory together with substantial computer capacities allows investigating small transition metal clusters with ab initio methods. Several studies, for example, have addressed properties of small cl
Data Loading...
