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

The magnetic phase diagram of γ-Mn alloys contains both collinear and noncollinear magnetic phases in fct and fcc crystal structures. Using a two-band model which incorporates the magnetoelastic coupling, we find that the gap (Formula presented) in the spin-wave dispersion is proportional to the 3/2 power of the sublattice magnetization (Formula presented) 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 (Formula presented) where 2Δ is the energy gap in the quasiparticle spectrum.