METALLIC MAGNETISM IN AMORPHOUS CO-Y ALLOYS

Magnetic properties of amorphous Co-Y alloys are investigated on the b asis of a finite-temperature theory of amorphous magnetic alloys. The numerical results show that the enhanced Curie temperatures (T(C)) inc rease linearly from a critical concentration of ferromagnetic instabil ity towards amorphous pure Co with increasing Co concentration. The en hancement of T(C) beyond 90 at. % Co is caused by the magnetic energy gain due to the structural disorder, while it is dominated around 60 a t. % Co by the change of Co-Y neighboring pairs and related change of coordination number of Co atoms. The calculated magnetization vs conce ntration curves show good agreement with the experimental data. They a re explained by the 3d-4d hybridization in the electronic states. It i s predicted that the effective Bohr magneton numbers show a minimum ar ound 55 at. % Co because of the occurrence of weak ferromagnetism.