Inelastic Neutron Scattering Investigation of Magnetic Excitations in the Quenched and Decomposed Samples of the $Mn_{0.75}Cu_{0.25}$ Alloy

The influence of spinodal decomposition on the spin wave characteristics in the $Mn_{0.75}Cu_{0.25}$ alloy was studied with inelastic neutron scattering. The measurements were performed on the quenched and annealed samples at a few temperatures. Parameters of spin-wave dispersion-relation for small wave-vector were derived. The values of spin wave velocity and energy gap obtained at reduced temperature $T//T_{N}$ ≈ 0.65 are after decomposition twice higher than for the quenched sample. For the decomposed sample the values of both parameters are close to the results published for the $Mn_{0.9}Cu_{0.1}$ alloy. This fact confirms that after decomposition spin waves are present in the sample regions of Cu concentration close to 0.1 and that the neighborhood of regions with high Cu content seems not to influence them. The spin wave velocity for the quenched sample is lower than observed in any other manganese alloy.