Local structure and ferromagnetic character of Fe-B and Fe-P amorphous alloys

We present clear experimental evidence that the dissimilar magnetic behavior of Fe-B and Fe-P amorphous alloys is connected with differences in the local structure around Fe atoms and with the different ferromagnetic character that these systems present. Structural parameters, obtained by x-ray absorption fine structure, show that Fe-Fe nearest distances are responsible for the behavior of the Curie temperature. Both magnitudes increase with increasing the metalloid content for Fe-B and remain constant for Fe-P. The results from x-ray magnetic circular dichroism reveal that Fe-B behaves as a weak ferromagnet in all the composition range while Fe-P evolves from a weak to strong ferromagnetism character when P concentration increases. This fact determines the behavior of the magnetic moment with increasing metalloid content that displays a large decrease for Fe-P and a negligible variation for Fe-B.