Novel diffractometer optimized for the study of weak superlattice reflections using crossed parabolic mirrors

Abstract

We present the development of a novel laboratory-based diffractometer optimized for high intensity and resolution matched to that of flux grown single crystal transition metal–oxide samples studied in solid state physics. This has been implemented using crossed graded d-spacing parabolic multilayer mirrors, a severely off-cut asymmetric analyzer crystal, and a microminiature cryostat. We demonstrate that the wider bandpass of the multilayer mirrors provides a significant increase in intensity compared to the use of silicon and germanium optics, but still provides the necessary resolution to obtain accurate measurements for inverse correlation lengths. The increase in flux allows the observation of features that were previously only visible with third generation synchrotron x-ray sources, shown by the observation of the very weak charge order peak without the use of a synchrotron source. Results on samples previously studied show an increase of a factor of 10 in intensity, coupled together with a factor of 7.5 increase in resolution over the previous system employed using a rotating anode source and flat pyrolytic graphite (0001) crystals. With such a diffractometer it is now possible to carry out detailed studies of charge ordering in transition metal oxides in the laboratory and the benefits of this are threefold. First, this will improve the quality of any preparation work, for subsequent experiments at synchrotron sources. This has the advantage of maximizing the efficiency of synchrotron measurements. Second, the enhanced intensity and resolution will allow experiments to be conducted in the laboratory which previously required access to synchrotron sources. Third, it will allow for synchrotron time to be used for its unique properties, i.e., wavelength tunability and polarization, which are necessary for the observation of magnetic reflections and orbital ordering by means of resonant enhancements and polarization analysis. This means that laboratory based measurements can be easily incorporated with synchrotron data, maximizing the potential of both techniques and receiving a net gain in data output.