SPIN-DENSITY WAVES IN DILUTE CUMN ALLOYS

Neutron scattering studies on concentrated CuMn alloys show static spin density waves (SDW) that are incommensurate with the lattice and which become dynamic above the freezing temperature T(f) with a dispersion relation that is essentially vertical. The existence of both the static and the dynamic SDW in dilute CuMn alloys where the Mn atoms may be separated beyond the range of SDW stability was examined. There is no such cutoff range in the Overhauser SDW model where the transition temperature is simply linear with concentration, but a recent calculation by Ioffe and Feigel'man gives magnetic order that does depend on an interaction range and the density of spins on the lattice. For CuMn alloys, they obtain spin-glass ordering at low Mn concentration with a crossover to short-range helical order near 10% Mn. Our neutron scattering measurements were made on single crystals of CuMn alloys containing 1.4% and 3.0% Mn. Elastic scans along [1zeta0] at temperatures well below T(f) yield the same type of intensity distribution as that previously observed for the more concentrated alloys and show the existence of static SDW at dilutions down to 1.4% Mn. Inelastic scans in the same Q region for the Cu-3% Mn alloy clearly show the presence of dynamic SDW at temperatures up to T/T(f) = 7.5. These results favor the SDW model of Overhauser as the best description of the magnetic order in dilute CuMn alloys.