Spin gap of the one-dimensional CuO2 chains in Sr14-yYyCu24O41-delta

We have measured the magnetic susceptibility chi of Sr14-yYyCu24O41-delta consisting of two-dimensional Cu2O3 planes, namely, so-called spin-1/2 ladders with two legs and also of one-dimensional CuO2 chains. The susceptibility chi(chain)(T) due to the CuO2 chains, obtained by subtracting the susceptibility chi(ladder)(T) due to the Cu2O3 planes from the experimental data of chi(T), is described by the Curie-Weiss law at T > T-max similar to 80 K, where chi exhibits the maximum for y = 0. With increasing y, chi(chain) becomes large owing to the increase of Cu2+ spins introduced into the CuO2 chains. Moreover, the antiferromagnetic interaction between Cu2+ spins in the CuO2 chains becomes weak with the increase in y, namely, with the increase of Cu2+ spins introduced into the CuO2 chains, leading to suppression of the spin gap of the CuO2 chains. As the result, the broad peak of chi, observed around 80 K for y = 0, is found to disappear for y greater than or equal to 1.0.