Neutron scattering from MnCu alloys near the critical composition: effects of stress and aging

A neutron diffraction study of the effects of applied stress and aging on MnCu alloys, 63.4 and 71.7 at% Mn, has provided information on the various contributions to the diffuse peak near 100 and the decomposition of the alloys in the two-phase (α + γ) region. In stress-orientated antiferromagnetic alloys the cusp-like scattering at 001 has been shown to arise from spin waves, and that at 1 1/2 0 from magnetic defect scattering. Magnetic short range order scattering, also at 1 1/2 0, is observed for the paramagnetic alloys. Comparisons of total scattering with elastic-only scattering experiments at various temperatures support these findings. The high damping capacity reported previously for these alloys after appropriate heat treatment is associated with the early stages of aging and the formation of a fine, coherent antiferromagnetic γMn precipitate. Prolonged aging results in an incoherent αMn precipitate in a Mn-depleted γ phase matrix. In MnCu, unlike MnNi alloys, aging does not produce a change in the shape of the diffuse peak: only a reduction in amplitude. (author)