Change of magnetoresistivity and magnetic structure of by iron substitution

Alloyed ( Mn 1 - x Fe x ) Au 2 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 MnAu 2 and the field-driven transition from helix to fan spin-structure. The threshold field H thr 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.