The Use of Mesoporous Systems for Preparation of One-Dimensional Ordered Magnetic Nanowires

Abstract

Here we report the synthesis and investigation of iron and iron oxide nanowire arrays using mesoporous silica as a host material. In the present work a novel variant of synthesis of ordered magnetic nanowires in the mesoporous silica matrix was suggested. The method is based on the incorporation of a hydrophobic metal compound into the hydrophobic part of silica-surfactant composite. The amount of iron intercalated into the mesoporous matrix was measured by chemical analysis. In all samples it corresponds well to with the molar ratio SiO2: Fe = 9:1. To provide crystallinity of nanowires additional thermal treatment was performed. Thus prepared nanocomposites were characterized by TEM, ED, SAXS, SANS, BET and magnetic measurements. The anisotropy parameters of nanowires were determined using two non-correlated methods: temperature dependence of magnetic susceptibility and small angle polarized neutron scattering. It was found that the particle length increases with the increasing of the decomposition temperature of the metal complex. Obviously it deals with crystallization and growth of metal particles inside the pores at a constant diameter of a single particle. For iron containing sample annealed at 375 °C (form factor of nanowire is about 40), the coercive force at room temperature was found to be 145 Oe at saturation magnetization of 1.2 emu/g, which is not far from modern information storage. It was shown that particles shape and size are in good agreement with that of the pores. Particles are uniform and well ordered in the silica matrix. Thus, the suggested method leads to one-dimensional anisotropic nanostructures which could find an application as high-density data storage magnetic media.

Preparation of strontium hexaferrite nanowires in the mesoporous silica matrix (MCM-41)

“…The presence of coercive force for samples obtained below 400 1C deals with a rather wide distribution of magnetically correlated volumes. Being compared to direct oxidation of iron pentacarbonyl complex in the mesoporous structure [2], the magnetic susceptibility of the composites increases several times. Thus, the strontium ions serve as a structure directing agent for the formation of the magnetic ferrite phases.…”

“…For example, highly anisotropic magnetic nanowires possess ferromagnetic properties at room temperature even at diameters of 2 nm. Recently iron and iron oxide nanowires with characteristic widths of 1-2 nm and different length/ diameter ratios were synthesized in the mesoporous silica matrix [2]. However, magnetic characteristics of these composites still need to be improved for their further use in magnetic storage media with ultrahigh areal density.…”

Synthesis of functional nanocomposites based on solid-phase nanoreactors

“…Napolskii et al 132 and Eliseev et al 140 considered the prospects of magnetic nanocomposites obtained on the basis of epitaxial mesoporous SiO 2 films in storage devices with ultrahigh data density. It is known that mesoporous SiO 2 forms epitaxial films on certain supports [e.g., on Si (110)].…”

Micron scale and nanoscale structure of mesoporous silica thin films

“…The formation mechanisms, the types of space group, and the synthetic parameters of the surfactant-directing silica thin films have been studied [2][3][4][5][6]. The potential applications of the mesoporous silica thin films reported include membrane-based separations [7], low-k dielectrics sensors [8], semiconductors [9], optoelectronic devices [4], high-density information storage media [10,11], thermoelectric devices [12], and medical treatment [13]. The most common synthetic route of the mesoporous silica thin films is based on the self-assembly [3,14] occurring in the solutions of organic precursors and amphiphilic entities which leads to the formation of mesophases with various geometries.…”