Two-dimensional tetramer-cuprate Na
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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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NICPB , Tallinn , Estonia: R. Stern I. Heinmaa A. Kriisa E. Joon NHMFL,Tallahassee, USA: P. Kuhns

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Nicpb tallinn estonia r stern i heinmaa a kriisa e joon nhmfl tallahassee usa p kuhns

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


Nicpb tallinn estonia r stern i heinmaa a kriisa e joon nhmfl tallahassee usa p kuhns

ResolvedNa+ Sites in RT MAS NMR/14.1T, νrot=40kHz

100

50

0

-50

-100

-150

-200

ppm


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


Nicpb tallinn estonia r stern i heinmaa a kriisa e joon nhmfl tallahassee usa p kuhns

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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