A MOLECULAR-DYNAMICS APPROACH TO MAGNETIC-ALLOYS WITH TURBULENT COMPLEX MAGNETIC-STRUCTURES - GAMMA-FEMN ALLOYS

A molecular dynamics (MD) approach to magnetic alloys with complex mag netic structures is proposed on the basis of the temperature control M D method and the functional integral technique. The theory allows us t o determine automatically the magnetic structure of a large system wit h a few hundred atoms in a unit cell. Numerical calculations for gamma -FeMn alloys have been performed using 108 atoms in a unit cell. It is demonstrated that gamma-FeMn alloys form various complex magnetic str uctures due to competing interactions: the 'first-kind' antiferromagne tic structure for less than 20 at.% Fe, the helix-like structure for 2 0 at.% Fe, noncollinear structures between 30 and 60 at.% Fe, the coll inear-like structure for 65 at.% Fe, noncollinear structures between 7 0 and 80 at.% Fe, collinear structures between 85 and 95 at.% Fe, and the helical structure for gamma-Fe. The average magnetic moments calcu lated from these structures are shown to explain the concentration dep endence--in particular, the existence of the peculiar minimum of the a verage magnetic moment at 50 at.% Fe.