On the magnetic structure of γ-FeMn alloys

The alloy gamma-FeMn is a rare example of a fcc antiferromagnet. It has become a prototype for pinning layer studies in magnetoelectronic devices. Here we report the results of first principles calculations of the magnetic structure of gamma-FeMn based on large cell models of the disordered alloy. The calculations are based on the constrained local moment model and use of first principles spin dynamics to obtain the ground state orientational configuration. In agreement with previous layer KKR-CPA studies, we find the 3Q-state to be lowest of the three prototype structures studied (1Q,2Q,3Q). However, the constraining fields introduced into the theory to maintain a specific orientational configuration are not zero indicating that even the 3Q-structure is not the ground state. Subsequent optimization of the magnetic configuration using first principles spin dynamics yields a state that is lower in energy by 2.5 meV/atom. (C) 2002 American Institute of Physics.