Structural and magnetic changes in FeNbCuSiB amorphous alloys during the crystallization process

Calorimetric and magnetic measurements, x-ray powder diffraction and Mossbauer spectroscopy have been used to study the magnetic and structural changes occurring after each of the two steps of crystallization that take place in FeNbCuSiB-type alloys. Two samples with different boron and silicon concentrations, Fe73.5Nb3Cu1Si22.5-xBx (x = 6, 9), have been studied. They give a somewhat different composition of the crystalline phases appearing after crystallization processes. The most noticeable phenomenon is the observed increase of about 50 K in the Curie temperature of the FeSi crystalline phase between the end of the first crystallization process and the end of the second one, although the composition of this phase remains unchanged. This result is discussed in terms of crystal boundary effects. Also, the Curie temperature of the remaining amorphous phase, in the crystallized samples, is greater than the expected one, due to the coupling with magnetic phases with higher Curie points and inhomogeneities in such a phase.