Ambient temperature synthesis of fine metal particles in montmorillonite clay and their magnetic properties

Abstract

Abstract Nanostructured, amorphous metallic particles containing some boron have been produced at ambient temperatures in the montmorillonite clay matrix by a reduction of the ion-exchanged M2+-montmorillonite (M = Fe, Co and Ni) with sodium borohydride. The products have been characterized by X-ray powder diffraction, chemical analysis, Transmission Electron Microscopy and SQUID magnetometer measurements. The Ni-B particles are 10–30 nm in size while the Co-B and Fe-B particles are 50–200 nm. The Co and Ni systems exhibit superparamagnetic behavior, while the Fe system shows ferromagnetism. The differences in magnetic properties among the three systems are explained on the basis of the changes in magnetic anisotropy energy that arise from compositional inhomogeneities; the compositional inhomo geneities are related to the ease with which the three M2+ ions can be reduced.