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 co
rrelations represented by broad humps close to (1, 1/2, 0)-type positions w
hile 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 centr
ed on (1, 1/2, 0) positions. The latter are superposed on a quasi-uniform '
background' of magnetic scattering representing a large fraction of the spi
n system frozen into quasi-random orientations at low temperatures. We sugg
est that the periodic nature of the lattice and the relatively strong magni
tudes of the antiferromagnetic first-neighbour and ferromagnetic second- an
d 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 enha
nce the latter at the expense of the uniform cross-section representing the
randomly frozen spin system. (C) 1999 Elsevier Science B.V. All rights res
erved.