First-principles study on the non-collinear magnetic structures of disordered alloys

The first-principles calculations for FeMn and MnPt alloys both of ordered and disordered phases have been performed with the TB-LMTO method combined with the CPA. The magnetic structure of FeMn in the disordered phase is suggested to be non-collinear 3Q structure where the average moment is around 1.7μ_B and the Neel temperature estimated from the effective exchange constant is about 550 K. For MnPt system, the high stability of the ordered phase may be closely related to the pseudo-gap formed at the Fermi level, which is brought about by the collinear antiferromagnetic (AF) staggered field. Accordingly, the calculated Neel temperature is quite high (∼760 K) as much as the measured value (∼1000 K). In the disordered phase, on the other hand, the random distribution eliminates the pseudo-gap and the magnetic structure turns likely to be 3Q structure with the Neel temperature down to around the room temperature.