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Title: Orbital Dimer Model for the Spin-Glass State in Y 2 Mo 2 O 7

The formation of a spin glass generally requires that magnetic exchange interactions are both frustrated and disordered. Consequently, the origin of spin-glass behavior in Y 2Mo 2O 7-in which magnetic Mo 4+ ions occupy a frustrated pyrochlore lattice with minimal compositional disorder-has been a longstanding question. Here, we use neutron and x-ray pair-distribution function (PDF) analysis to develop a disorder model that resolves apparent incompatibilities between previously reported PDF, extended x-rayabsorption fine structure spectroscopy, and NMR studies, and provides a new and physical explanation of the exchange disorder responsible for spin-glass formation. We show that Mo 4+ ions displace according to a local "two-in-two-out" rule on each Mo 4 tetrahedron, driven by orbital dimerization of Jahn-Teller active Mo 4+ ions. Long-range orbital order is prevented by the macroscopic degeneracy of dimer coverings permitted by the pyrochlore lattice. Cooperative O 2- displacements yield a distribution of Mo-O-Mo angles, which in turn introduces disorder into magnetic interactions. In conclusion, our study demonstrates experimentally how frustration of atomic displacements can assume the role of compositional disorder in driving a spin-glass transition.
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [3] ;  [4] ;  [5] ;  [4] ;  [1] ;  [1]
  1. Univ. of Oxford, Oxford (United Kingdom)
  2. Univ. of Oxford, Oxford (United Kingdom); Rutherford Appleton Lab., Oxfordshire (United Kingdom); Georgia Inst. of Technology, Atlanta, GA (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
  4. Rutherford Appleton Lab., Oxfordshire (United Kingdom)
  5. Rutherford Appleton Lab., Oxfordshire (United Kingdom); Diamond Light Source, Oxfordshire (United Kingdom); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 118; Journal Issue: 6; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
Rutherford Appleton Laboratory, ISIS Pulsed Neutron and Muon Facility; STFC Daresbury Laboratory; Engineering and Physical Sciences Research Council (EPSRC); European Research Council (ERC); Argonne National Laboratory, Advanced Photon Source; USDOE
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
OSTI Identifier:
1390903
Alternate Identifier(s):
OSTI ID: 1343354