nicpb , tallinn , estonia: r. stern i. heinmaa a. kriisa e. joon nhmfl,tallahassee, usa: p. kuhns
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Two-dimensional tetramer-cuprate Na5RbCu4(AsO4)4Cl2 :
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
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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Na5RbCu4(AsO4)4Cl2
a
c
Cu
O
As
a
c
a
c
a
c
Cu
O
As
nearly tetragonal nearly tetragonal insulating insulating magnetic materialmagnetic material
The copper and The copper and oxygen ions form oxygen ions form square tetramer square tetramer units units Cu4O44
spin exchange is spin exchange is expected to be expected to be two-dimensionaltwo-dimensional
S.-J. Hwu et al., J. Am. Chem. Soc., 124, 12404 (2002)
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NMR study ofNMR study of Na5RbCu4(AsO4)4Cl2
The experiments are performed at 8,45T and The experiments are performed at 8,45T and 14,1T14,1T ( (4K4K << TT << 300K300K))
We used powders and small single crystalsWe used powders and small single crystals On powders we employed MASOn powders we employed MAS (12K < T < (12K < T <
300K)300K) All attempts to see Cu NMR above TAll attempts to see Cu NMR above TNN have have
yet been unsuccessfulyet been unsuccessful We have measured We have measured 8787Rb, Rb, 3535Cl and Cl and 2323Na NMR Na NMR
spectraspectra
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High-resolution magic-angle spinning (MAS) NMRMAS) NMR
SSampleample is rotated is rotated about about an axis oriented at an axis oriented at 54.74° with54.74° with respect to respect to BB00
Sidebands become Sidebands become insignificant when insignificant when spectral width is smaller spectral width is smaller than than rotation frequencyrotation frequency
Our rotation frequencyOur rotation frequency: : 20 20 ÷÷ 40 kHz 40 kHz
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100 50 0 -50 -100 -150 -200
ppm
Resolved Na+ Sites in RT MAS NMR/14.1T, νrot=40kHz
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2323Na MASNa MAS
200 100 0 -100 -200 -300 -400
ppm
40.7K
72.4K
85.6K
86.3K
87.4K
104.3K
106.3K
107.4K
139.0K
203.5K
294.5K
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Na5RbCu4(AsO4)4Cl2: single crystal 87Rb NMR
(i) 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
-300 -200 -100 0 100 200
9.80 K
10.80 K
11.76 K
12.70 K
13.86 K
14.05 K
14.13 K
14.25 K
14.42 K
Shift from RbCl [kHz]
B0 = 14.1 T || [010]
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0 50 100 150 200 250 3001600
1800
2000
2200
2400
2600
2800
87
Rb Quadrupolar Coupling
87νQ∝VZZ
[ ]kHz
[ ]Temperature K
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0 50 100 150 200 250 300
50
100
150
200
250
10
20
30
40
50
satellite transition (3/2 ↔ 1/2) (-3/2 satellite transition↔ -1/2)
[ ]Linewidth of the satellites kHz
[ ]Temperature K
(1/2 central transition↔ -1/2)
[ ] Linewidth of the central transition kHz
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ConclusionConclusion
0 50 100 150 200 250 300
Temperature [K]
PMLT1LT2AFM
11
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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