X-band ESR and 51V NMR study of the haldane system PbNi2-xMgxV2O8

The temperature and angular dependence of the X-band electron spin resonance (ESR) and V-51 nuclear magnetic resonance (NMR) spectra have been measured in a recently discovered Haldane-gap system, PbNi2-xMgxV2O8, (0 less than or equal to x less than or equal to 0.24). The angular dependence of the ESR signal suggests that both the spin diffusion as well as the magnetic anisotropy determine the electronic spin correlation functions. However, in doped samples the magnetic anisotropy increasingly dominates the spin dynamics on cooling. The huge broadening of the V-51 NMR spectra in doped samples at low temperatures provides evidence for localized magnetic moments in the vicinity of the Mg impurities. Locally distorted structure around each Mg impurity may slightly modify the magnetic interactions and be potentially responsible for the antiferromagnetic ordering (below T-N approximate to 3.5 K) in doped compositions.