Magnetism and phase stability of fcc Fe-Co alloys precipitated in a Cu matrix

The magnetism and phase stability of Fe-rich fcc Fe-Co alloys precipitated in a Cu matrix were studied by measuring the magnetization in the in situ condition during a precipitation heat treatment for the sample of Cu₉₈(Fe_1-xCo_x)₂ (x⩽0.55). It was found that fcc Fe-Co becomes ferromagnetic for x>0.4. The Curie temperature and the spontaneous magnetization were determined. They exhibit a similar concentration dependence to fcc Fe-Ni alloys, indicating Invar phenomena at the critical concentration. By observing the thermal hysteresis of magnetization change for various heat sequences the fcc-to-bcc transition was detected for x>0.3 and its transition temperature was determined. The stability of the fcc phase was discussed in terms of the lattice misfit and the Invar effect.