Our studies of the itinerant antiferromagnetic -Mn-based alloys are extended to investigate magnetic excitations in a Mn(13.7%Ni) alloy. The composition of the present sample being close to the part of the phase diagram where a number of structural phase transitions take place, the basic aim of this work is the search for the effect of these transitions on spin dynamics. This is the first study of the Mn - Ni alloy in the fct (c < a) phase. The parameters of the spin wave dispersion relation and their temperature dependence are determined and compared with those for Mn - Ni alloys in the fct (c > a) and fcc phases. We obtain the concentration dependence of the low-temperature parameters of the spin wave dispersion relation which differs essentially from that found for the Mn - Fe alloys. In particular the change of the spin wave parameters in the vicinity of the phase transitions in Mn - Ni alloys is remarkable.

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A systematic study of temperature dependence of magnetic inelastic neutron scattering for itinerant antiferromagnet Mn(12%Ge) is presented. At low temperatures the experimental data are well described in terms of damped spin waves. This description becomes insufficient at least 150 K below TN. In the temperature range 200-400 K the integrated intensity of distribution for energy transfer 13 THz increases by one third and the shape of the deconvoluted neutron scattering cross-section changes. These changes suggest that ca. 200 K below TN an additional contribution to the inelastic neutron scattering starts to appear and that its origin is different from spin waves.PACS numbers: 75.30.Ds, 75.50.EeThe magnetic excitations in itinerant antiferromagnets are not yet satisfactorily understood. In particular more detailed studies of their temperature dependence are needed. The aim of our experiment was to study the evolution of the neutron scattering by spin waves at low temperature into the paramagnetic scattering above TN.The crystal structure of the γ-Mn alloys with high: manganese concentration (fcc in the paramagnetic phase) becomes tetragonal with c < a in the antiferromagnetic (AF) phase. Many alloys with lower manganese concentration remain fcc in the AF phase. In some narrow concentration region (different for different diluents) two other crystal structures: orthorhombic and tetragonal with c > a appear in the AF phase. The composition of the investigated alloy is close to the composition for the tricritical point for paramagnetic fcc, AF tetragonal and AF (483)

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The interest in magnetic properties of DO 3 -type alloys stems from their ability to exhibit dependence of magnetic moments on local environment. It is shown that both, static and dynamic properties of the alloys based on Fe 3 Si and Fe 3 Al require further investigations. This concerns mainly the problem of selective substitution of chromium for iron, as well as spin dynamics, the latter problem is illustrated on the example of measured spin waves in Sendust.

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The inuence of spinodal decomposition on the spin wave characteristics in the Mn0.75Cu0.25 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 /TN ≈ 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 Mn0.9Cu0.1 alloy. This fact conrms 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 inuence them. The spin wave velocity for the quenched sample is lower than observed in any other manganese alloy.