Direct observation of phase coherence in 3-k magnetic configurations

Abstract

We report the observation by neutron diffraction of phase coherent Bragg reflections in a multi-k magnetic configuration with a spatial periodicity outside the conventional scattering cross-section. The peaks, which exist in the 3-k state of UAs_0.8Se_0.2, display long-range order with a wavevector dependence characteristic of a magnetic interaction. The results confirm the long-range order and temperature dependence reported in an earlier study of similar peaks in this material using X-ray resonant scattering by (a) the non-trivial extension to the technique of neutron diffraction, and (b) the observation of similar 3-k phase-coherent reflections in other samples by X-ray resonant scattering. The importance of the neutron diffraction results lies primarily in the fact that magnetic neutron diffraction is well established as a weak probe operating on thermodynamic time scales. This alleviates concern that the rapid (10⁻¹⁵–10⁻¹⁴ s), strong interaction, characteristic of the resonant X-ray technique, is imaging a transient or non-equilibrium configuration. Likewise, the extension of the X-ray resonant scattering results to other samples establishes the generality of this effect. The enigma of how to understand the observed diffraction, which appears to lie strictly outside both the conventional neutron and X-ray scattering cross-sections, remains.

Keywords:

• Neutron scattering
• Non-collinear magnetic structures
• Multiple order parameters

Acknowledgements

EB, PJ and SBW would like to thank the European Commission for support in the frame of the ‘Training and Mobility of Researchers’ programme. This work was performed at the Institut Laue-Langevin, France, the European Synchrotron Radiation Facility, France, and the Swiss neutron spallation source SINQ, at the Paul Scherrer Institut, Switzerland; access to the Swiss neutron spallation source has been supported by the European Commission under the 6th Framework Programme through the Key Action: Strengthening the European Research Area, Research Infrastructures. Contract number: RII3-CT-2004-505925. Part of this work was made possible thanks to the support of the European Community-Access to Research Infrastructures action of the Improving Human Potential Programme in allowing access to the Actinide User Laboratory at the Institute for Transuranium Elements-Karlsruhe under Contract No. HPRICT-200100118.