Ferromagnetism and ordering in Fe-Co alloys

Results of our experimental investigation on the magnetization, specific heat, and neutron diffraction in Fe-Co alloys are reported and interpreted by a statistical theory in B-W approximation. The exchange interactions between neighboring atoms in bcc are determined so that the theory reproduces the experimental magnetization versus temperature curves. The ordering energy is fixed so that the theory predicts the order-disorder transformation at 730°C as observed experimentally in the alloy with 50 atomic percent Co. The theory implies also that the nonmagnetic state, should it exist, would undergo the order-disorder transformation at about 550°C. An attempt is made to interpret the observed anomalies in terms of a coexistence of magnetic and nonmagnetic states in these alloys and to relate the specific heat with the neutron diffraction data.