The impurity-induced antiferromagnetic ordering of the doped Haldane magnet Pb(Ni{1-x}Mg{x})2V2O8 (0 < x <0.06) was studied by electron spin resonance (ESR) on ceramic samples in the frequency range 9-110 GHz. Below the N\'{e}el temperature a transformation of the ESR spectrum was found, indicating an antiferromagnetic resonance mode of spin precession. The excitation gap of the spin-wave spectrum increases with increasing Mg-concentration x in the same manner as the N\'{e}el temperature, reaching its maximum value of 80 GHz at x > 0.04. At small concentrations x < 0.02 the signals of antiferromagnetic resonance were found to coexist with the signal of the paramagnetic resonance indicating a microscopic separation of the magnetic phases.
@article{arxiv.cond-mat/0112443,
title = {Paramagnetic and antiferromagnetic resonances in the diamagnetically diluted Haldane magnet PbNi2V2O8},
author = {A. I. Smirnov and V. N. Glazkov and H. -A. Krug von Nidda and A. Loidl and L. N. Demianets and A. Ya. Shapiro},
journal= {arXiv preprint arXiv:cond-mat/0112443},
year = {2009}
}