Anomalous magnetic properties of the nano-size residual amorphous phase in nanocrystals

D Kaptás, T Kemény, J Balogh, L Bujdosó, LF Kiss, Tamás Pusztai1, I Vincze

1Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, P.O. Box 49, Budapest H-1525, Hungary

The composition dependence of the Curie temperature and the
magnetic moment of the nano-size residual amorphous phase in
partially crystallized Fe92-xZr7B,Cu-1 (2 less than or equal to
x less than or equal to 23) amorphous alloys were determined by
Fe-57 Mossbauer spectroscopy. Both quantities show broad minima
and for increasing relative Zr content (i.e, for decreasing B
concentration) surpass the usual monotonic decrease observed for
the bulk counterparts. The deviation does not scale with the
characteristic size of the residual amorphous regions, which was
found to be constant, ruling out explanations based on
interphase exchange interaction. A magnetovolume origin of the
observed anomalous composition dependence and the improved soft-
magnetic characteristics of these nanocrystals is proposed.