NMR study of the doped chain compounds 2-x xD. Arcon1, 2, A. Zorko1 and A. Lappas3
1 Institute "Jozef Stefan" - Jamova 39, 1000 Ljubljana, Slovenia
2 Faculty of Mathematics and Physics, University of Ljubljana Jadranska 19, 1000 Ljubljana, Slovenia
3 Institute of Electronic Structure & Laser Foundation for Research & Technology-Hellas P.O. Box 1527, 711 10 Heraklion, Crete, Greece
(Received 28 July 2003; accepted in final form 23 October 2003)
NMR has been measured in polycrystalline chain compounds 2-x x ( x = 0, 0.12, 0.24 ) between room temperature and 4 . A broad strongly shifted resonance has been found in all three cases, suggesting that tetrahedra serve as a superexchange bridge between chains. The temperature dependence of the first moment of the NMR lines demonstrates the existence of a spin-gap down to very low temperatures even in doped samples. On the other hand, the large inhomogeneous broadening of the NMR spectra and the spin-lattice relaxation data suggest that short-range antiferromagnetic correlations already develop at and coexist with the 1D magnetic excitations in the -substituted derivatives. In addition, we propose that not all NMR centres remain equivalent after doping. Namely, in -doped samples we find an intense, narrow NMR line whose origin is compatible with the deformed tetrahedra.
75.50.Ee - Antiferromagnetics.
75.10.Jm - Quantized spin models.
76.60.-k - Nuclear magnetic resonance and relaxation.
© EDP Sciences 2004