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 c ondition during a precipitation heat treatment for the sample Of CU98 (Fe1- xCOx)(2) (x less than or equal to 0.55). It was found that fcc Fe-Co become s ferromagnetic for x > 0.4. The Curie temperature and the spontaneous magn etization were determined. They exhibit a similar concentration dependence to fcc Fe-Ni alloys, indicating Invar phenomena at the critical concentrati on. 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 d iscussed in terms of the lattice misfit and the Invar effect.