A group from the University of Warwick, ISIS and the ILL carried out single crystal diffraction experiments using both polarised and unpolarised neutrons to identify two distinct types of short-range magnetic order at low temperatures in SrHo2O4. Their results have been published in Physical Review B.
SrHo2O4 belongs to the SrLn2O4 (where Ln = Lanthanide) family of compounds, in which the magnetic Ln3+ ions form honeycomb layers joined by a network of zigzag chains. In the presence of antiferromagnetic exchange interactions, these exhibit geometric frustration. The crystal structure of SrHo2O4 allows for two crystallographically inequivalent sites for the Ho3+ ions. The group used neutron diffraction on WISH at ISIS and D7 and D10 at the ILL to study the low temperature magnetic structure of SrHo2O4.
They have found that SrHo2O4 displays no long-range order down to at least 50 mK, but two distinct types of short-range magnetic order coexist in the material that shows no chemical instability or phase separation. The first type of magnetic order is characterised by the appearance of broad diffuse scattering peaks around k = 0 positions in the (hk0) scattering plane, as shown in Fig. 1. The data were collected using the WISH diffractometer. The second type of magnetic order reveals itself through the planes of diffuse scattering intensity at the (hk ±l/2) positions. This observation suggests that the second type of short-range order present in SrHo2O4 is principally one-dimensional in nature, that is the magnetic structure is essentially a collection of antiferromagnetically coupled chains running along the c-axis with the intrachain correlations remaining rather weak down to lowest temperatures. The authors suggest that the two types of magnetic structure arise from the two crystallographically inequivalent sites for the Ho3+ ions in the unit cell.
Olga Young is a final year PhD student in the Superconductivity and Magnetism Group based in the Physics Department, Warwick University. She says, "In order to study the effects of geometrical frustration on various systems it is crucial to be able to look at the large sections of reciprocal space quickly and with a good resolution, particularly at the ultra-low temperatures. WISH is an ideal instrument in this respect."
Pascal Manuel is the instrument scientist on WISH. He says, “The principal aim of WISH was powder diffraction with single crystal capability. We’ve been very successful with powder diffraction with over 20 publications already, but this is the first paper on a single crystal sample. We needed a lot of software development so this paper is partly the result of some hard work from the Mantid development team, making it possible for the users to analyze the huge volume of data that comes with single crystal experiments.”
Jon Taylor leads the Mantid project. He says, “"One of the objectives of the Mantid project is to deliver high quality scientific software for the ISIS user program. The WISH instrument generates large volume datasets which by definition requires high performance specialist software to enable visiting scientists and ISIS staff to probe the collected data in an efficient and productive fashion in order to determine the crystallographic and magnetic structures. The Mantid development team has over the last year put a large amount of effort into efficient visualisation of single crystal neutron diffraction data, which will not only benefit users of Wish and SXD but also users of MAPS, MERLIN and LET. It is excellent news that the software that is developed jointly by ISIS and SNS has made such an immediate impact in this area."
Pascal Manuel and Sara Fletcher
Research date: July 2013
Highly frustrated magnetism in SrHo2O4: Coexistence of two types of short-range order,
O. Young, A. R. Wildes, P. Manuel, B. Ouladdiaf, D. D. Khalyavin, G. Balakrishnan, and O. A. Petrenko, Physical Review B 88, 024411 (2013).