A transition from ferromagnetic structure to flat spiral structure was observed in a groups of transition metal alloys. The space group is Pnma and the magnetic Mn atoms occupy 4c position. How to understand the occurrence of spiral structure in such compounds?
It is know that Dzyaloshinskii-Moriya interaction due to spin-orbit coupling is responsible for the spiral structure in some multiferroics oxides. However, this interaction just occur in the sample without centrosymmetry. In my sample, the Pnma structure is centrosymmetric, and this interaction cannot occurs. Is there some other interactions or models to explain the spiral magnetic structure in centrosymmetric transition metal alloys?
For transition metal alloys, the interaction should be itinerant or direct interaction?
Sometimes, the electrons localize and delocalized partially. In this case, should the interaction be RKKY?
DM interaction (if it is allowed by symmetry in your sample) might be responsible only for the long (small q) spin spirals. Usually spirals is stabilized in Mn based materials by the competition of the few nearest neighbor exchanges with different signs. Look at the discussion of classical MnAu2 helimagnets given by Udvardi et al. PRB(2006), or Glasbrenner et al. PRB (2010)
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