Showing papers by "Kirill S. Napolskii published in 2004"

Magnetic properties of iron nanoparticles in mesoporous silica

Abstract: Magnetic properties of nanocomposites based on mesoporous silica SiO 2 with embedded iron particles are studied by small angle polarized neutron scattering at temperatures from 8 to 300 K and magnetic fields from 1 to 350 mT. This mesoporous silica forms highly regular hexagonal structures of nanotubes. A diffraction peak in SANS at q c =1.55 nm −1 is observed, corresponding to a hexagonal structure with periodicity a =4.6 nm. The scattering of the pure matrix Si0 2 is well fitted by a sum of two contributions: Porod scattering from large particles (1/ q 4 ) plus the scattering on a regular structure of pores (diffraction peak). Additional scattering is observed from samples with iron in the pores. The latter is fitted as scattering from bunches of nanowires with an average radius of R b =4.68 nm and a spread of Δ R b =0.9 nm. The nuclear-magnetic interference in the scattering of polarized neutrons is studied. We observe no interference scattering on the periodic structure that would be consistent with a hexagonal structure of nanotubes/nanowires. Instead, appreciable interference scattering is detected which is directly related with bunches of nanowires created during crystallization. The temperature and magnetic field dependences of this interference scattering demonstrate a transition from superparamagnetic to dipole–glass state at T = 80 K caused by an interplay of magnetic field, dipole–dipole, and thermal interactions.

Mesoporous Aluminosilicates as a Host and Reactor for Preparation of Ordered Metal Nanowires

Abstract: The creation of functional nanomaterials with the controlled properties is emerging as a new area of great technological and scientific interest, in particular, it is a key technology for developing novel high-density data storage devices. Today, no other technology can compete with magnetic carriers in information 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 other hand, the use of purely nanocrystalline systems is limited because of their low stability and tendency to form aggregates. These problems could be solved by encapsulation of nanoparticles to a chemically inert matrix. One of the promising matrices for preparation of highly anisotropic magnetic nanoparticles is mesoporous silica or mesoporous aluminosilicates. Mesoporous silica is an amorphous SiO2 with a highly ordered uniform pore structure (the pore diameter can be controllably varied from 2 to 50 nm). This pore system is a perfect reactor for synthesis of nanocomposites due to the limitation of reaction zone by the pore walls. One could expect that size and shape of nanoparticles incorporated into mesoporous silica to be consistent with the dimensions of the porous framework.