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Magnetoresistance and magnetization measurements on pure DyMn 6 Ge 6 and low-doped Dy(Mn 6 Ge 6 ) 1− x (Fe 6 Al 6 ) x samples x ≤ 0.05 with the hexagonal HfFe 6 Ge 6 -type structure are used to investigate the connection between magnetoresistance and magnetization processes in these compounds. At room temperature, DyMn 6 Ge 6 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.

A melt-textured bulk YBa2Cu3O7−x sample has been investigated by magnetization M(H) and magneto-resistance R(H) measurements in pulsed magnetic fields up to 50 T. We describe a technique which allowed us to determine the irreversibility fields Hirr from M(H) and R(H) curves. The irreversibility line shows linear behavior in the fields above 20 T which cannot be explained by present models.