We report 63Cu nuclear magnetic resonance and muon spin rotation measurements on the S=1/2 antiferromagnetic Heisenberg spin chain compound Sr1.9Ca0.1CuO3. An exponentially decreasing spin-lattice relaxation rate 1/T1 indicates the opening of a spin gap. This behavior is very similar to what has been observed for the cognate zigzag spin chain compound Sr0.9Ca0.1CuO2, and confirms that the occurrence of a spin gap upon Ca doping is independent of the interchain exchange coupling J′. Our results therefore generally prove the appearance of a spin gap in an antiferromagnetic Heisenberg spin chain induced by a local bond disorder of the intrachain exchange coupling J. A low temperature upturn of 1/T1 evidences growing magnetic correlations. However, zero field muon spin rotation measurements down to 1.5 K confirm the absence of magnetic order in this compound which is most likely suppressed by the opening of the spin gap.
@article{arxiv.1403.2890,
title = {Spin Gap in the Single Spin-1/2 Chain Cuprate Sr$_{1.9}$Ca$_{0.1}$CuO$_3$},
author = {F. Hammerath and E. M. Brüning and S. Sanna and Y. Utz and N. S. Beesetty and R. Saint-Martin and A. Revcolevschi and C. Hess and B. Büchner and H. -J. Grafe},
journal= {arXiv preprint arXiv:1403.2890},
year = {2014}
}