Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Magnetismus Poster: Do., 13:00–15:30 D-P233
Antiferromagnetic domains in RNi2B2C and GdNi2Ge2 - characterization
in reciprocal space and real space by neutron and x-ray diffraction
A. Kreyssig 1,2 , J. W. Kim 2 , C. Detlefs 3 , H. Klein 3 , A. Dreyhaupt 1 , L. Tan 2 ,
B. Grenier 4 , D. Wermeille 2,5 , A. I. Goldman 2 , M. Loewenhaupt 1
1 Institut für Festkörperphysik, Technische Universität Dresden, Germany – 2 Ames
Laboratory and Department of Physics and Astronomy, Iowa State University, Ames,
USA – 3 European Synchrotron Radiation Facility, Grenoble, France – 4 Institut Laue-
Langevin, Grenoble, France – 5 Advanced Photon Source, Argonne, USA
Magnetic domains are intensely investigated in ferromagnetic compounds according to
their application as hard or soft ferromagnetic materials. Numerous methods are deployed
to characterize the magnetic domain structure because of its strong influence on
the relevant extrinsic magnetic properties. Mostly these techniques are based on measurements
of the net magnetisation or on mapping of magnetic field inhomogeneities
at the domain borders. Studies of domains in antiferromagnetic materials naturally
request the usage of other signatures.
In this presentation we will motivate at first the study of domains in antiferromagnetic
materials. In general, the onset of antiferromagnetic order yields domains due to
the lowering of symmetry by the propagation vector or the moment direction. These
domains can play an important role, for instance, in the interplay between magnetism
and superconductivity due to the pinning effect of domain borders on superconducting
flux lines. Last but not least, the knowledge of the domain behavior is often necessary
to determine the microscopic magnetic structure unambiguously. For both cases, we
will present examples demonstrating different ways to characterize antiferromagnetic
domains. In RNi2B2C compounds (R = rare earth), superconductivity and antiferromagnetic
order can coexist. The antiferromagnetic domains are indirectly imaged
through their attendant magnetoelastic distortions using x-ray topography at ESRF
Grenoble. The results are discussed in relation to regularities in the domain arrangement
proven by satellite reflections in neutron and x-ray diffraction patterns measured
at ILL Grenoble and at Ames Laboratory. Consequences for the superconducting
properties are discussed. In GdNi2Ge2, the second example, direct imaging of antiferromagnetic
domains could be realised by x-ray resonant magnetic scattering and microscanning
across the sample surface at APS Argonne. Domain imaging was essential
to investigate the phase transition between the low-temperature spiral-like magnetic
order and the high-temperature collinear magnetic structure in detail, because both
magnetic structures would yield similar patterns in usual diffraction experiments due
to domain averaging.
We thank the groups of G. Behr and P. C. Canfield for the preparation of the
high-quality single crystals. We acknowledge the financial support by the Deutsche
Forschungsgemeinschaft through the SFB 463 and by the U. S. Department of Energy,
Office of Science under contracts W-7405-ENG-82 and W-31-109-ENG-38.