Effect of exchange anisotropy on the hysteresis behavior of Co particles : S. Gangopadhyay( a), G.C. Hadjipanayis( a), C.M. Sorensen( b) and K.J. Klabunde( c) (a)Department of Physics and Astronomy, University of Delaware, Newark, DE 19716. (b)Department of Physics, (c)Department of Chemistry, Kansas State University, Manhattan, KS 66506

Abstract

Previous studies have indicated that, as a function of the overall composition, the microstructure of Y-Fe alloy samples produced by the inert-gas condensation technique evolves in the following way: the size of the crystalline grains diminishes with increasing molar fraction of Fe,xFe, to reach aminimum value of about 2 nm at xFe = 0.3. In this composition region, Fe forms a segregation layer at the grain boundaries between the pure Y crystallites. For xFe > 0.3, the alloys are amorphous. This suggests that for the low Fe nanocrystalline samples, the interior of the grains is paramagnetic, whereas the grain boundaries form a 3-dimensional network, similar to a foam, in which the high concentration of Fe may promote ferromagnetic ordering. We present results of a magnetization and Mössbauer spectroscopy study of the magnetic properties of this novel microstructure. The data indicate that both ordered and non-ordered states of the grain boundary segregation layers exist. This is rationalized in terms of different values of the excess of Fe at the grain boundaries. The high XFe amorphous nanostructured samples are compared to literature data on melt-spun and sputtered amorphous Y-Fe. The results indicate that the tendency for clustering ofFe observed in melt-spun samples is enhanced in the nanostructured amorphous samples.