Structure of melt-quenched Pr-Fe alloys and analysis of the magnetization based on super-ferromagnetism

Non-equilibrium Pr100-xFex alloys (x=1, 4, 10, 20, 30, 40) prepared by melt-quenching were investigated by X-ray diffraction, VSM, Mossbauer spectroscopy and TEM observation. The experimental results indicated that, in the Pr-1 at%Fe alloy, iron atoms have little magnetic moment and may be dissolved in a dhcp-Pr matrix. In other compositions, iron atoms, having a magnetic hyperfine field of about 29 T (290 kOe) at 77K, are mainly in an amorphous phase. We analyze the magnetic data for Pr-10, 20, 30 at%Fe with the model based on super-ferromagnetism-magnetically connecting Fe-rich clusters dispersed in a non-magnetic matrix-, in which the inter-cluster interactions are treated as molecular field. The results show that the Curie temperature within clusters, T-c(intra), is nearly constant for all compositions, and that for inter-cluster coupling, T-c(inter), becomes higher toward T-c(intra) as the iron concentration increases. The analysis also shows that the average size of clusters increases with the iron concentration. It is suggested that the patches in an amorphous region observed in the TEM image of Pr-10at%Fe, each of which estimates to contain a few hundreds of atoms, behave as the super-ferromagnetic clusters.