Structure and magnetic properties of the S=1 geometrically frustrated double perovskites La2LiReO6 and Ba2YReO 6

Tomoko Aharen, John E. Greedan, Craig A. Bridges, Adam A. Aczel, Jose Rodriguez, Greg MacDougall, Graeme M. Luke, Vladimir K. Michaelis, Scott Kroeker, Chris R. Wiebe, Haidong Zhou, Lachlan M.D. Cranswick

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Two B-site ordered double perovskites, La2LiReO6 and Ba2 YReO6, with S=1 were investigated as geometrically frustrated antiferromagnets, using x-ray and neutron diffraction, superconducting quantum interference device magnetometry, heat capacity, muon spin relaxation (μSR), and 89Y magic-angle spinning (MAS) NMR. La2 LiReO6 has a monoclinic structure (P 21 /n) with cell parameters at room temperature; a=5.58262 (22) Å, b=5.67582 (20) Å, c=7.88586 (27) Å, and β=90.240 (4) °. A zero-field cooled/field cooled (ZFC/FC) divergence at 50 K was observed in the susceptibility. The ZFC susceptibility is zero below ∼5K for polycrystalline samples, suggesting a cooperative singlet ground state but weak moments are induced by cooling in very small fields ∼1mT. No evidence of long-range ordering is evident in heat capacity, neutron-diffraction, or μSR data. The ZF spin dynamics from μSR are anomalous and can be fitted to a stretched exponential rather than the Kubo-Toyabe form expected for random frozen spins but the muon spins are decoupled in longitudinal fields (LF), consistent with spin freezing of the fraction of spins relaxing within the muon time scale. The internal fields sensed by the muons are anomalously small, consistent with an electronic spin-singlet state. Ba2 YReO6 is found to be cubic (Fm3m) with cell parameter a=8.36278 (2) Å at 300 K with no change in symmetry at 3.8 K, at variance with the Jahn-Teller theorem for a t2g2 configuration for Re5+. 89Y MAS NMR shows a single peak indicating that Y/Re site disorder is at most 0.5%. The susceptibility shows two broad peaks around 50 and 25 K but no evidence for long-range order from heat capacity, neutron diffraction, or μSR. The ZF μSR result shows a two-component ground state with both slow and fast relaxations and decoupling results in a 1 kG LF, indicating spin freezing. These results are in sharp contrast to the long-range AF order found in the S=3/2 isostructural materials, La2 LiRuO6 and Ba2 YRuO6, indicating that the reduction to S=1 plays a major role in ground state determination.

Original languageEnglish (US)
Article number064436
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number6
StatePublished - Feb 26 2010
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics


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