SURFACE EFFECTS OF METALLIC IRON PARTICLES IN ZEOLITE NAX

In situ Mossbauer, magnetization, ferromagnetic resonance and small-an gle X-ray scattering measurements are used to characterize iron partic les in the zeolite NaX, prepared by thermal decomposition of Fe(CO)(5) . The examined system shows a bimodal size distribution of superparama gnetic alpha-Fe particles with mean diameters of 1.2 +/- 0.1 nm locate d inside the supercages and 3.0 +/- 1.0 nm located in defect sites of the zeolite. An enhancement of the saturation magnetization of the sma ller particles by about 30% with respect to the bulk value has been ob served. This enhancement is most likely due to surface effects of ultr a-small particles in which 90% of the atoms are surface atoms.