Change of magnetoresistivity and magnetic structure of MnAu2 by iron substitution

Alloyed (Mn1-xFex)Au2 ribbons (x=0-0.075) show a complex dependence of magnetization and magnetoresistivity on composition, magnetic field, and temperature. This is associated with the helimagnetism of MnAu2 and the field-driven transition from helix to fan spin-structure. The threshold field Hthr for this metamagnetic transition strongly depends on x. Neutron diffraction shows that the periodicity length of the helix increases with increasing iron contents x<0.075. For x=0.05 a transition from the helical ground-state to a collinear ferromagnetic structure takes place at 150 K; for x=0.075 only a ferromagnetic order is found.