Composition dependence of field induced anisotropy in ferromagnetic (Co, Fe)89Zr7B4 and (Co, Fe)88Zr7B4Cu1 amorphous and nanocrystalline ribbons

The composition dependence of field induced anisotropy K-U of field annealed soft ferromagnetic (Co1-xFex)(89)Zr7B4 and (Co1-xFex)(88)Zr7B4Cu1 amorphous and amorphous/nanocrystalline nanocomposite melt spun ribbons is investigated. With the exception of the highest Co-containing alloys (x< similar to 0.10), the observations are discussed in terms of a superposition of directional pair ordering of Fe,Co atoms and an additional contribution presumably due to the presence of Zr and B in both the field crystallized and field annealed amorphous ribbons. The highest Co-containing alloys (x < similar to 0.10) contain multiple nanocrystalline phases (bcc, fcc, and hcp) for which a peak in KU is observed (K-U similar to 2000-2500 J/m(3)). In this framework, asymmetry in the compositional dependence of KU resulting in larger values for Co-rich alloys relative to Fe-rich alloys for both the field crystallized and field annealed amorphous alloys is explained in terms of a strong dependence of the Curie temperature of the amorphous phase on the Co content. c 2008 American Institute of Physics. [DOI: 10.1063/1.3021141]