Magnetic Moment, Curie Temperature and Invar Effects in Amorphous Alloys

The magnetic moment, Curie temperature and Invar effects in amorphous alloys are briefly reviewed. The average magnetic moment μ of binary amorphous alloys of Fe, Co, and Ni with an early transition metal E shows a systematic trend, that is, the value of μ becomes larger as the valence and size differences between Fe, Co, Ni and E increase. Comparison of the experimental results with Friedel's model suggests that Co-E alloys exhibit strong ferromagnetism while Fe-E alloys present weak ferromagnetism. The concentration dependence of the Curie temperature T
_c
is similar to that of μ above 20% E in Fe-E alloys. However, in the dilute concentration range, T
_c
decreases very rapidly, resulting in spin glass behavior due to spin frustration. Invar effects such as a large thermal expansion anomaly and a remarkable pressure effect on T
_c
are common in Fe-based amorphous alloys. The anomalous behavior above T
_c
is closely related to magnetic inhomogeneity.