AMBIENT-TEMPERATURE SYNTHESIS OF FINE METAL PARTICLES IN MONTMORILLONITE CLAY AND THEIR MAGNETIC-PROPERTIES

Nanostructured, amorphous metallic particles containing some boron hav e been produced at ambient temperatures in the montmorillonite clay ma trix by a reduction of the ion-exchanged M(2+)-montmorillonite (M = Fe , Co and Ni) with sodium borohydride. The products have been character ized by X-ray powder diffraction, chemical analysis, Transmission Elec tron Microscopy and SQUID magnetometer measurements. The Ni-B particle s 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 inhomogeneiti es; the compositional inhomogeneities are related to the ease with whi ch the three M(2+) ions can be reduced.