Noncollinear magnetism of Fe-rich FeNi alloys

The magnetic structure of Fe-rich FeNi alloys has long been a subject of gr eat scientific interest and controversy. In this study, the authors attempt to understand an interesting phenomenon that the average magnetic moment o f the alloys in the gamma-phase (fcc) decreases dramatically in the composi tion range near 70% Fe. Although the observation was made more than 30 year s ago, the nature of the mechanism for this moment collapse is still contro versial. In this approach, the noncollinear locally self-consistent multipl e-scattering (LSMS) method is applied to the magnetic structure calculation of large unit cell samples consisting of Fe and Ni atoms. The Fe and Ni at oms are randomly distributed on a fee lattice. The moment directions are in itialized to be randomly oriented and then, as the self-consistent iteratio ns proceed, are allowed to rotate to minimize the total energy. A stable ma gnetic structure of the alloy is determined by the final moment configurati on. Results are compared with experiments and the possible existence of non collinear magnetic structures are discussed.