Anomalous lattice contraction and magnetism of γ-Fe precipitates in Cu

The lattice parameter of FCC ( gamma -)Fe precipitates in a Cu matrix is investigated as a function of the size of the precipitates. With prolonged aging, noncoherent gamma -Fe precipitates with about 0.2% smaller lattice spacings than the coherent ones are found. The structural phase transition, the magnetic structure and the Neel temperature of this new state are studied using X-ray and neutron diffraction methods. Antiferromagnetic ordering takes place accompanying a structural phase transition as in the coherent state. The observed Neel temperature is slightly higher than the previously reported value TN=67 K. Various magnetic properties of gamma -Fe precipitates in Cu are discussed on the basis of the present experimental data.