Atomic and magnetic correlations in a Cu-5 at % Mn spin-glass alloy

Measurements of atomic and magnetic correlations in the plane perpendicular to the [1, 0, 0] axis for a Cu-5 at% Mn single crystal at low temperatures using polarised neutrons give clear evidence of weak atomic short-range correlations represented by broad humps close to (1, 1/2, 0)-type positions while magnetic correlations are evidenced as strong low Q-scattering and SDW-like peaks at (1, 1/2 +/- delta, 0)-type positions, as well as humps centred on (1, 1/2, 0) positions. The latter are superposed on a quasi-uniform 'background' of magnetic scattering representing a large fraction of the spin system frozen into quasi-random orientations at low temperatures. We suggest that the periodic nature of the lattice and the relatively strong magnitudes of the antiferromagnetic first-neighbour and ferromagnetic second- and third-neighbour interactions give rise to the SDW-like short-range order while the effect of the small amount of atomic short-range order is to enhance the latter at the expense of the uniform cross-section representing the randomly frozen spin system. (C) 1999 Elsevier Science B.V. All rights reserved.