Mossbauer studies of ultrafine iron-containing particles on a carbon support

Carbon-supported metallic iron particles with an av. diam. of 3.7 nm have been studied in situ by Moessbauer spectroscopy in the temp. range 5-305 K and with external magnetic fields up to 4 T. Depending on the prepn. conditions various amts. of amorphous Fe-C particles are also formed. The av. magnetic hyperfine fields of the surface atoms of a-Fe particles are significantly larger than that of bulk a-Fe at 5 K, but decrease much faster with increasing temp. than the bulk hyperfine field. The superparamagnetic blocking temp. for the a-Fe particles is about 70 K, but after oxidn. it decreases to about 50 K, indicating that the magnetic anisotropy energy const. of the oxidized particles is significantly lower than that of the metallic particles. The temp. dependence of the spectral area is similar in the metallic and the oxidized states. In both cases the vibrational modes are dominated by particle vibrations. [on SciFinder (R)]