Spin-Gap Behavior of CuNb2O6

Abstract

The magnetic properties of two polymorphs of CuNb 2 O 6 with quasi-one-dimensional zig-zag spin ( S =1/2) chains of Cu 2+ ions are studied. The magnetic excitation spectra of Cu spins measured by neutron scattering, and the T -dependence of the longitudinal spin relaxation rate of 93 Nb nuclei by NMR indicate the existence of the spin gap in the monoclinic phase whose magnitude is consistent with the one deduced by the detailed analyses of uniform magnetic susceptibility at low temperatures. The behavior in the monoclinic phase is in clear contrast to that found in the orthorhombic phase.