Surface effects of metallic iron particles in zeolite NaX

In situ Mössbauer, magnetization, ferromagnetic resonance and small-angle X-ray scattering measurements are used to characterize iron particles in the zeolite NaX, prepared by thermal decomposition of Fe(CO)₅. The examined system shows a bimodal size distribution of superparamagnetic α-Fe particles with mean diameters of 1.2+-0.1 nm located inside the supercages and 3.0 ±1.0 nm located in defect sites of the zeolite. An enhancement of the saturation magnetization of the smaller particles by about 30% with respect to the bulk value has been observed. This enhancement is most likely due to surface effects of ultra-small particles in which 90% of the atoms are surface atoms.