Spin-wave gap and spin dynamics of γ-Mn alloys

The magnetic phase diagram of gamma-Mn alloys contains both collinear and noncollinear magnetic phases in fct and fee crystal structures. Using a two-band model which incorporates the magnetoelastic coupling, we find that the gap Delta(sw)(T) in the spin-wave dispersion is proportional to the 3/2 power of the sublattice magnetization M(T), in agreement with experiments on both the collinear and noncollinear magnetic phases. For the noncollinear magnetic phases observed in MnNi and FeMn alloys, high-frequency excitations are predicted with omega((q) over right arrow=0)similar to Delta, where 2 Delta is the energy gap in the quasiparticle spectrum.