Local and average structures of the spin-glass pyrochlore Y2Mo2O7 from neutron diffraction and neutron pair distribution function analysis

Greedan, J. E.; Kim, H.-J.; Lozano-Gorrin, A. D.; Bozin, E.; Derahkshan, S.; Proffen, Th.; Gout, D.; Billinge, S. J. L.

doi:10.1103/PhysRevB.79.014427

Journal Article

Local and average structures of the spin-glass pyrochlore Y2Mo2O7 from neutron diffraction and neutron pair distribution function analysis

Greedan, J. E. ; Gout, D.FZJ* ; Lozano-Gorrin, A. D. ; Derahkshan, S. ; Proffen, T. ; Kim, H.-J. ; Bozin, E. ; Billinge, S. J. L.

2009
APS College Park, Md.

Physical review / B 79(1), 014427 (2009) [10.1103/PhysRevB.79.014427]

This record in other databases:

Please use a persistent id in citations: http://hdl.handle.net/2128/11034 doi:10.1103/PhysRevB.79.014427

Abstract: The observation of canonical spin-glass behavior in the pyrochlore oxide Y2Mo2O7 has been a subject of considerable interest as the original structural studies were interpreted in terms of a well-ordered crystallographic model. It is widely held that the stabilization of the spin-glass state requires some level of positional disorder along with frustration. Recent reports from local probe measurements, extended x-ray-absorption fine structure (EXAFS) and Y-89 NMR, have been interpreted in terms of disorder involving the Mo-Mo distances (EXAFS) and multiple Y sites (NMR). This work reports results from temperature-dependent (15-300 K) neutron diffraction (ND) and neutron pair distribution function studies which can provide from the same data set information on both the average and local structures. The principal findings are that: (1) there is no crystallographic phase transition over the temperature region studied within the resolution of the ND data; (2) the diffraction data are well fitted using a fully ordered model but with large and anisotropic displacement parameters for three of the four atomic sites; (3) the pairwise real-space correlation function G(r) shows clear evidence that the principal source of disorder is associated with the Y-O1 atom pairs rather than the Mo-Mo pairs, in disagreement with the interpretation of the EXAFS results; (4) fits to the G(r) improve significantly when anisotropic displacements for all sites are included; (5) inclusion of a split-site position parameter for O1 improves, slightly, both the G(r) fits and the Rietveld fits to the ND data; and (6) for all models the fits become worse as the temperature decreases and as the fitting range decreases. These results are qualitatively consistent with the Y-89 NMR observations and perhaps recent muon-spin-relaxation studies. The issue of static versus dynamic disorder is not resolved, definitively. An estimate of the distribution of exchange constants due to the disorder is made using spin-dimer analysis and compared with the Saunders-Chalker model for the generation of spin-glass behavior from "weak" disorder on geometrically frustrated lattices.

Keyword(s): J ; exchange interactions (electron) (auto) ; frustration (auto) ; neutron diffraction (auto) ; spin glasses (auto) ; yttrium compounds (auto)

Classification:

Physics, Condensed Matter

Note: J.E.G. thanks the Natural Sciences and Engineering Research Council of Canada for support through a Discovery Grant. A. D. L.-G. thanks the Spanish Ministry of Education for support. The authors thank I. P. Swainson for helpful discussions. This work benefited from the use of NPDF at the Lujan Center at Los Alamos Neutron Science Center, funded by DOE Office of Basic Energy Sciences. Los Alamos National Laboratory is operated by Los Alamos National Security LLC under DOE Contract No. DE-AC5206NA25396. The upgrade of NPDF was funded by NSF through Grant No. DMR00-76488. Work by the Billinge group was supported by the Office of Science, U. S. Department of Energy, under Contract No. DE- AC02-98CH10886.

Contributing Institute(s):

Research Program(s):

Appears in the scientific report 2009

Database coverage:
American Physical Society Transfer of Copyright Agreement