SPIN-WAVE GAP AND SPIN DYNAMICS OF GAMMA-MN ALLOYS

The magnetic phase diagram of gamma-Mn alloys contains both collinear and noncollinear magnetic phases in fct and fee crystal structures. Us ing a two-band model which incorporates the magnetoelastic coupling, w e find that the gap Delta(sw)(T) in the spin-wave dispersion is propor tional to the 3/2 power of the sublattice magnetization M(T), in agree ment 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.