NMR characterization of spin-1/2 alternating antiferromagnetic chains in   the high-pressure phase of (VO)2P2O7
  Local-susceptibility measurements via the NMR shifts of $^{31}$P and $^{51}$V nuclei in the high-pressure phase of (VO)$_{2}$P$_{2}$O$_{7}$ confirmed the existence of a unique alternating antiferromagnetic chain with a zero-field spin gap of 34 K. The $^{31}$P nuclear spin-lattice relaxation rate scales with the uniform spin susceptibility below about 15 K which shows that the temperature dependence of both the static and dynamical spin susceptibilities becomes identical at temperatures not far below the spin-gap energy. 
J. Kikuchi, K. Motoya, T. Saito, M. Azuma and M. Takano