Iron nanowires embedded in mesoporous silica: Polarized neutron scattering study

Abstract

Magnetic iron nanowires embedded in the mesoporous silica matrix have been studied by Small Angle Polarized Neutron Scattering. Magnetic nanocomposites were prepared by a novel variant of the synthesis based on the introduction of the hydrophobic metal compound, Fe(CO)5, into the hydrophobic part of as-prepared mesoporous silica-surfactant composite. The mesoporous silica represents a highly regular hexagonal structure of mesopores. A diffraction peak in SAPNS at qc≈1.55 nm−1 is observed, which corresponds to a hexagonal structure with a periodicity of a0≈4.6 nm. The scattering pattern of the pure matrix SiO2 is well fitted by a sum of the contributions: the scattering on a powder consisting of large particles (1/q4) and the scattering on the regular structure of pores (diffraction peak). The samples with iron inside the pores give additional scattering. This scattering depends significantly on the annealing temperature what demonstrates the different degrees of crystallization process. The latter is fitted as a scattering on the bunches of the nanowires with average radius Rb and with its spread ΔR. The nuclear–magnetic interference in scattering of polarized neutrons was also studied. We observe no interference scattering on the periodical structure. Instead, a significant interference scattering is detected, which may be directly related to the bunches of the nanowires created during the crystallization process.