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NICPB , Tallinn , Estonia: R. Stern I. Heinmaa A. Kriisa E. Joon NHMFL,Tallahassee, USA: P. Kuhns

Two-dimensional tetramer-cuprate Na 5 RbCu 4 (AsO 4 ) 4 Cl 2 : phase transitions and AFM order as seen by NMR. NICPB , Tallinn , Estonia: R. Stern I. Heinmaa A. Kriisa E. Joon NHMFL,Tallahassee, USA: P. Kuhns A. Harter A. Reyes W. Moulton.

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NICPB , Tallinn , Estonia: R. Stern I. Heinmaa A. Kriisa E. Joon NHMFL,Tallahassee, USA: P. Kuhns

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  1. Two-dimensional tetramer-cuprate Na5RbCu4(AsO4)4Cl2 :phase transitions andAFMorder as seen byNMR NICPB, Tallinn, Estonia: • R. Stern • I. Heinmaa • A. Kriisa • E. Joon NHMFL,Tallahassee, USA: • P. Kuhns • A. Harter • A. Reyes • W. Moulton Department of Chemistry, Clemson University, USA: • M. Kartin-Ulutagay • X. Mo • W. Queen • S.-J Hwu Physics Department, Miami University USA: • J. Clayhold

  2. Na5RbCu4(AsO4)4Cl2 • nearly tetragonal insulating magnetic material • The copper and oxygen ions form square tetramer units Cu4O4 • spin exchange is expected to be two-dimensional S.-J. Hwu et al., J. Am. Chem. Soc., 124, 12404 (2002)

  3. NMR study ofNa5RbCu4(AsO4)4Cl2 • The experiments are performed at 8,45T and 14,1T (4K<T<300K) • We used powders and small single crystals • On powders we employed MAS(12K < T < 300K) • All attempts to see Cu NMR above TN have yet been unsuccessful • We have measured 87Rb, 35Cl and 23Na NMR spectra

  4. High-resolution magic-angle spinning(MAS) NMR • Sample is rotated about an axis oriented at 54.74° withrespect to B0 • Sidebands become insignificant when spectral width is smaller than rotation frequency • Our rotation frequency: 20 ÷ 40 kHz

  5. ResolvedNa+ Sites in RT MAS NMR/14.1T, νrot=40kHz 100 50 0 -50 -100 -150 -200 ppm

  6. 294.5K 203.5K 139.0K 107.4K 106.3K 104.3K 87.4K 86.3K 85.6K 72.4K 40.7K 200 100 0 -100 -200 -300 -400 ppm 23Na MAS

  7. Na5RbCu4(AsO4)4Cl2: single crystal 87Rb NMR B0 = 14.1 T || [010] • Direct observation of the transition into the AFM ordered phase • (TN = 14.3 K in B0 = 14.1 T) • (ii) The complicated low-T 87Rb NMR line shape suggests a complicated, incommensurate (IC) ordered phase • (iii) A plane-wave modulated IC spin state? Stern, et al., unpublished

  8. AFM LT1 PM LT2 T 74 110 0 50 100 150 200 250 300 N Temperature [K] Conclusion

  9. Acknowledgements NICPB, Tallinn, Estonia: • R. Stern • I. Heinmaa • A. Kriisa • E. Joon NHMFL,Tallahassee, USA: • P. Kuhns • A. Harter • A. Reyes • W. Moulton Department of Chemistry, Clemson University, USA: • M. Kartin-Ulutagay • X. Mo • W. Queen • S.-J Hwu Physics Department, Miami University USA: • J. Clayhold

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