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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 comparison of the suppression of antiferromagnetism in metals as a function of temperature or high magnetic fields provides a deep probe of the nature of the metallic state as well as the antiferromagnetic order. Here we report magnetization and resistivity measurements of the metallic antiferromagnets Mn3Si (TN=25 K), CuMnSb (TN=50 K) and PdMnTe (TN=17 K) in pulsed magnetic fields up to μ0H=50 T and temperatures down to 4.2 K. Experiments were performed at the Dresden high magnetic field facility. The low antiferromagnetic ordering temperatures in these compounds combined with the ordered magnetic moments known from neutron scattering studies show that we access for the first time equivalent magnetic and thermal energy scales in transition metal antiferromagnets. While Mn3Si and CuMnSb exhibit a bulk magnetization of only a fraction of the ordered moment up to 50 T, PdMnTe shows a trend towards saturation. We speculate that in particular the tiny response of Mn3Si and CuMnSb up to 50 T are related to a strong asymmetry of the density of majority to minority charge carriers. Such a trend would be naturally supported in the Heusler structure of these compounds as originally proposed for NiMnSb and PtMnSb, in which the absence of minority charge carriers is referred to as half-metallic ferromagnetism.

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.

We have used point-contact (PC) spectroscopy on 1:6:6 rare earth:transition metal:metal compounds with complex magnetic order. The limiting compounds of the alloy series DyGe 6 Fe 6− x Mn x are the helimagnet DyGe 6 Mn 6 with antiferromagnetic coupling of Mn- and Dy-sublattices and DyFe 6 Ge 6 showing antiferromagnetic order in the Fe-sublattice but only an independent order of the Dy-sublattice at low temperature. Here, we present new PC data for melt-spun ribbons using homocontacts and heterocontacts with Cu.

The novel ternary compound CeCo 9 Si 4 has been studied by means of specific heat, magnetization and transport measurements. Single-crystal X-ray refinements reveal a fully ordered distribution of Ce, Co and Si atoms with the tetragonal space group I4/mcm isostructural with other RCo 9 Si 4 . The smaller lattice constants of CeCo 9 Si 4 in comparison with the trend established by other RCo 9 Si 4 is indicative for intermediate valence of cerium. While RCo 9 Si 4 with R = Pr , … Tb , and Y show ferromagnetism and LaCo 9 Si 4 is nearly ferromagnetic, CeCo 9 Si 4 remains paramagnetic even in external fields as large as 40 T, though its electronic specific heat coefficient ( γ ≃ 190 mJ / mol K 2 ) is of similar magnitude as that of metamagnetic LaCo 9 Si 4 and weakly ferromagnetic YCo 9 Si 4 .