材料科學與工程學系

 演講公告

Speaker

A.A. Eliseev; K.S. Napolskii; A.V. Lukashin; Yu.D. Tretyakov
Department of Materials Science, Moscow State University, Moscow, Russian Federation

Title Chemical Design of Magnetic Nanocomposites Based on Mesoporous Matrices.
Time 14:00~16:00, Monday, April 16, 2007
Place 材料系館2F 俊銘講堂( 4436)
Abstract

     Modern information technologies require development of novel high-density data storage devices due to colossal growth of digital information volume. Today, no other technology can compete with magnetic information carriers in storage density and access rate. However, usually very small (10-1000 nm3) magnetic nanoparticles shows para- or superparamagnetic properties, with very low blocking temperatures and no coercitivity at normal conditions. One possible solution of this problem is preparation of highly anisotropic nanostructures. From the synthetic point of view, the synthesis of high-quality nanostructures usually involves the use of geometrically confined systems at nanolevel as a reactor for preparation or crystallization of particles. Usually, a nanoreactor is formed by colloidal species, such as in Langmuir-Blodgett films, self-assembling multilayers, reversed micelles, liquid crystals etc. However these pathways do not allow us to control the anisotropy of the particles which are most important for better understanding of physics of magnetization at nanolevel and practical application. From the other hand, the use of purely nanocrystalline systems is limited because of low stability and tendency to form aggregates. These problems could be solved by encapsulation of nanoparticles in an inert matrix.

     Thus, in the present study the influence of the anisotropy parameters of the magnetic metal and metal oxide nanowires formed in the structural cavities of solid state nanoreactors (zeolites, mesoporous silica and anodic alumina membranes) to the magnetic properties was carried out. The first two types enabled us to investigate the influence of the preparation conditions to the physical properties of magnetic nanowires. The use of the anodic alumina membranes allowed to incorporate various compounds by electrodeposition, which enables simple handling over loading values and anisotropy of nanowires. Thus these types of nanoreactors made it possible to investigate the influence of anisotropy of nanowires on their magnetic properties in wide range of the aspect ratio of the nanoparticles. The study represents the formation of magnetic, semiconductor and catalytic nanocomposites based on the metallic (Fe, Ni, Pt, Fe-Co, Fe-Pt alloys, etc) and metal oxide (α-Fe2O3, γ-Fe2O3, Fe3O4, etc) nanowires.

     Incorporation of metals was studied by chemical analysis TEM, ED, SAXS, SANS, BET and magnetic measurements. It was showed that particles shape and size are in good agreement with that of the pores. Particles are uniform and well ordered in the matrices. The anisotropy parameters of the magnetic wires were determined using two non-correlated methods: temperature dependence of magnetic susceptibility and small angle polarized neutron scattering. It was found that the anisotropy factor of metal nanowires attain the value of ~ 40. Such wires (is case of iron) represent high coercive force up to 460 Oe (at 300K) and saturation magnetization of 3 emu/g, which is nearly enough for modern information storage. Besides the control over diameter of the pores enables us to define the anisotropy parameters of nanowires. Thus, our approach leads to functional materials with nanosized active elements in the matrices, which could find an application in various fields of engineering and technology.