Spin-Vacancy-Induced Long-Range Order in a New Haldane-Gap Antiferromagnet

Abstract

Magnetic susceptibility, high-field magnetization, and inelastic neutron scattering experiments are used to study the magnetic properties of a new $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ quasi-one-dimensional antiferromagnet ${\mathrm{PbNi}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{8}$. Interchain interactions are shown to be almost, but not quite, strong enough to destroy the nonmagnetic singlet ground state and the energy gap in the magnetic excitation spectrum. Substituting nonmagnetic ${\mathrm{Mg}}^{2+}$ ( $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$) ions for ${\mathrm{Ni}}^{2+}$ ( $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$) induces a magnetically ordered state at low temperatures. To our knowledge this is the first observation of doping-induced long-range order in a Haldane-gap system.