Münster 1999 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 6: Niederdimensionale Spinsysteme
TT 6.6: Vortrag
Montag, 22. März 1999, 16:15–16:30, F2
23Na NMR Study of the Lattice Dimerisation in the Spin-Peierls Compound α-NaV2O5 — •Y. Fagot-Revurat1, M. Mehring1, and R. K. Kremer2 — 1U. Stuttgart, 2. Phys. Inst., 70550 Stuttgart — 2MPI f. Festk"orperforschung, 70569 Stuttgart
A new magneto-elastic transition at TSP=35 K has been reported two years ago in α-NaxV2O5 providing thus the second example of known inorganic spin-Peierls compounds. As far as the magnetic properties are concerned, this system belongs to the standard S=1/2 Heisenberg Antiferromagnetic Chain Model but the possible mixed valency between two adjacent Vanadium sites has led to a redefinition of this compound as a quarter-filled ladder compound made of weakly coupled V4+ and V5+ chains with the spins S=1/2 carried by V-O-V orbitals on the rungs of the ladder (instead of adjacent magnetic chain of V4+ carrying the spins S=1/2 and diamagnetic V5+ chains). The resulting dimerized structure should be thus more complicated than in a standard S=1/2 HAFC Model involving both charge and spin degree of freedom. We present here an overview of 23Na(I=3/2) data obtained in a chemically well characterized crystalline sample (x=0.996, TSP=34.95 K). We determined the full T-dependence of both electric field gradient and magnetic hyperfine shift tensors at the Na sites from 10 to 300 K. The lattice distortion leads to a progressive quadrupolar splitting of the NMR lines coupled to the order parameter of the SP-transition. The unexpected great number of quadrupolar sites below TSP support the assumption of an unusual lattice modulation wavevector kSP=1/2,1/2,1/4 proposed in order to explain INS measurements. Some dynamic effects associated with the T-dependence of (1/T1) will be discussed and additional 51V(I=7/2) NMR data will be also presented. - PAUSE -