The antiferromagnetism of manganese copper alloys

Manganese-rich γ phase alloys of manganese + copper have been investigated by neutron and X-ray diffraction techniques, and the temperature variations of magnetic susceptibility and electrical resistivity have been measured. The disappearance of long-range antiferromagnetic ordering has been correlated with the face-centred-tetragonal → face-centred-cubic marten-sitic transformation of these alloys. The Néel temperatures and the magnetic moments of the manganese ions, for alloys of various compositions, have been determined. The Néel temperature increases approximately linearly with increasing manganese content and extrapolates to 660° K at 100 % Mn; the value of 2⋅4 ± 0⋅1 μ B has been obtained for the ionic moment of the manganese ions in pure γ -Mn. Experiments on plastically strained specimens show that compressive stress results in alinement of the c axes of the crystallites along the [100]-type direction most nearly parallel to the stress axis. The ionic moments are alined along the c axis and the susceptibility of plastically strained specimens is anisotropic. An analysis is given of the results of measurements of the anisotropy of susceptibility from which may be calculated χ ∥ and χ ⊥ , the susceptibilities of a single antiferromagnetic domain measured respectively parallel and perpendicular to the direction of antiferromagnetism. The results of the investigations are discussed in terms of an electron band model of an antiferromagnetic metal.