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

Peter Kerschl 2Nadezda V. Kozlova 2Zbigniew Śniadecki 1Konstantin Nenkov 2Ulrich K. Rößler 2Bogdan Idzikowski 1,2Karl-Hartmut Müller 2Ludwig Schultz 2

1. Polish Academy of Sciences, Institute of Molecular Physics, Mariana Smoluchowskiego 17, Poznań 60-179, Poland
2. Leibniz-Institute for Solid State and Materials Research, P.O.Box 270116, Dresden D-01171, Germany

Abstract

Hexagonal DyMn6Ge6 with HfFe6Ge6 structure is a prototypical rare-earth transition-metal compound with complex magnetic couplings. Rare-earth and transition metal ions order simultaneously in a ferrimagnetic helix with locally anti-parallel moments of the sublattices at a high transition temperature (TC = 423 K). This layered magnetic system is a suitable experimental model for studies on the relation between magnetization processes and magnetoresistance in complex metallic alloys. Field and temperature-dependent spin-reorientation in this compound cause anomalies of the electrical resistivity and sizeable magnetoresistance effects.

We report results from measurements of the magnetoresistance and magnetization in static and pulsed fields up to 50 T for polycrystalline samples of pure and diluted Dy(Mn6Ge6)1-x(Fe6Al6)x. The samples were prepared by melt-spinning and subsequent annealing. Annealed pure and low-doped samples x<0.05 have the HfFe6Ge6-structure. At room-temperature, the pure compound shows negative magnetoresistance MR(H) = (R(H) - R(0)) / R(0), that reaches about 7% at 4 T and displays a marked change of slope at the helix-fan-transition near 5 T. Below 100 K, positive magnetoresistance is found with a non-monotonic dependence MR(H) in high fields above 20 T. The anomalous decrease of MR(H) is explained by a metamagnetic behaviour related to a transition from the ferrimagnetic fan into a spin-flop state. For low substitutions of MnGe by FeAl (x = 0.01) an increase of the specific resistivity and reduced magnetic ordering-temperatures are found. Near the helix-magnetic ordering temperature, an anomaly of the resistivity occurs indicating a strong influence of magnetic impurity-scattering on electronic transport. As-quenched and more strongly alloyed samples show different crystalline phases, derived from the hexagonal TbCu7-type structure, but have similar magnetoresistive behaviour.

This work is supported by BMBF project: 03SC5DRE.

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Presentation: poster at E-MRS Fall Meeting 2005, Symposium D, by Zbigniew Śniadecki
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-30 07:18
Revised:   2009-06-07 00:44
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