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Title: Unstable spin-ice order in the stuffed metallic pyrochlore Pr2+xIr2-xO7-δ

Specific heat, elastic neutron scattering, and muon spin rotation experiments have been carried out on a well-characterized sample of “stuffed” (Pr-rich) Pr2+xIr2-xO7-δ. Elastic neutron scattering shows the onset of long-range spin-ice “2-in/2-out” magnetic order at 0.93 kelvin, with an ordered moment of 1.7(1) Bohr magnetons per Pr ion at low temperatures. Approximate lower bounds on the correlation length and correlation time in the ordered state are 170 angstroms and 0.7 nanosecond, respectively. Muon spin rotation experiments yield an upper bound 2.6(7) milliteslas on the local field B4floc at the muon site, which is nearly two orders of magnitude smaller than the expected dipolar field for long-range spin-ice ordering of 1.7-Bohr magneton moments (120–270 milliteslas, depending on the muon site). This shortfall is due in part to splitting of the non-Kramers crystal-field ground-state doublets of near-neighbor Pr3+ ions by the positive-muon-induced lattice distortion. For this to be the only effect, however, ~160 Pr moments out to a distance of ~14 angstroms must be suppressed. An alternative scenario—one consistent with the observed reduced nuclear hyperfine Schottky anomaly in the specific heat—invokes slow correlated Pr-moment fluctuations in the ordered state that average B4floc on the μSR time scale (~10-7 second), but are staticmore » on the time scale of the elastic neutron scattering experiments (~10-9 second). In this picture, the dynamic muon relaxation suggests a Pr3+ 4f correlation time of a few nanoseconds, which should be observable in a neutron spin echo experiment.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [5] ;  [5] ;  [6] ;  [7] ;  [8] ;  [4] ;  [4] ;  [9] ;  [4] ;  [4]
  1. Univ. of California, Riverside, CA (United States); Univ. of Tokyo, Chiba (Japan)
  2. California State Univ., Los Angeles, CA (United States)
  3. Univ. of California, Riverside, CA (United States); Fudan Univ., Shanghai (China)
  4. Univ. of Tokyo, Chiba (Japan)
  5. John Hopkins Univ., Baltimore, MD (United States)
  6. John Hopkins Univ., Baltimore, MD (United States); National Institute of Standards and Technology, Gaithersburg, MD (United States)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  8. John Hopkins Univ., Baltimore, MD (United States); National Institute of Standards and Technology, Gaithersburg, MD (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  9. Univ. of Tokyo, Chiba (Japan); Japan Science and Technology Agency, Saitama (Japan)
Publication Date:
OSTI Identifier:
1213348
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 92; Journal Issue: 5; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY