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Published online by Cambridge University Press: 17 March 2011
Nanocrystalline Fe85Zr7B6Cu2 and Fe87.2Zr7.4B4.3Cu1.1 (at. %) samples have been obtained by annealing Melt-spun ribbons for 1hr at various temperatures in the range 593K to 953K. Structural characterization by means of X-ray diffraction and thermomagnetic analyses reveal the manifestations of Fe nanocrystals embedded in an amorphous matrix. The coercive field has been measured by a Förster coercimeter at temperatures ranging between 50 K and 300 K, and the room temperature domain structure has been monitored by magneto-optical Kerr effect. Both, the as cast as well as the sample annealed above 813K display soft magnetic properties at room temperature, exhibiting a coercive field below 10 A/m, and wide regular domains. In contrast, the samples annealed at 750 K, corresponding to the beginning of the crystallization process, undergo a magnetic hardening, showing higher coercive fields (up to 150 A/m for Fe87.2Zr7.4B4.3Cu1.1) and a dull domain pattern. When these magnetically harder samples are cooled, their coercivity is reduced. Thus, the magnetic hardening is attributed to the exchange decoupling between crystallites, due to the proximity of the Curie temperature of the amorphous phase.