Magnetic excitations around magnetic Brillouin zone centre in antiferromagnetic Mn(13.7%Ni) alloy

Our studies of the itinerant antiferromagnetic gamma-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.