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


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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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slide1
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
na 5 rbcu 4 aso 4 4 cl 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)

nmr study of na 5 rbcu 4 aso 4 4 cl 2
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
high resolution m agic angle spinning mas nmr
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
23 na mas

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
slide8

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Stern, et al., unpublished

conclusion

AFM

LT1

PM

LT2

T

74

110

0

50

100

150

200

250

300

N

Temperature [K]

Conclusion
acknowledgements
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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