Magnetoresistance and magnetization processes in the helimagnetic compound DyMn6Ge6 and in related alloys Dy(Mn6Ge6)1−x(Fe6Al6)x

Magnetoresistance and magnetization measurements on pure DyMn6Ge6 and low-doped Dy(Mn6Ge6)1−x(Fe6Al6)x samples x ≤ 0.05 with the hexagonal HfFe6Ge6-type structure are used to investigate the connection between magnetoresistance and magnetization processes in these compounds. At room temperature, DyMn6Ge6 shows negative magnetoresistance MR(H), which is related to a transition from a ferromagnetic helix state into a fan state in this compound. Below 100 K, positive MR(H) is found with a non-monotonic dependence in fields above 20 T. The anomalous behavior of MR(H) is explained by a sequence of transitions from conical helix to conical fan and a field-driven canting in the ferromagnetic Dy-Mn-subunits at higher fields. This transition transforming the ferrimagnetic fan into a ferromagnetic spin-flop state is discernible as a macroscopic metamagnetic behavior in the magnetization curves. For low substituted samples an increase of the specific resistivity and reduced magnetic ordering temperatures are found. Their MR(H) at high temperatures displays a similar negative behavior as the pure compound. The anomalous low-temperature magnetoresistance behavior is absent in the alloyed samples.