Study on the magnetic susceptibility of Li1−xNaxCu2O2 single crystals

Li1−xNaxCu2O2 (x=0, 0.05, 0.10, and 0.20) single crystals were synthesized by the self-flux method, and the temperature dependent magnetic susceptibility χ(T) were measured along the c axis. Na doping at the Li sites induces almost no change in the temperature (about 40 K) corresponding to the maximum of magnetic susceptibility. However, it results in the upturn of the magnetic susceptibility in the low temperature region (T<14 K), which could be attributed to the filling of the spin-gap. The behaviors of magnetic susceptibility in the high temperature region (T>60 K) of all the samples were well fitted by the spin S=1/2 chain frustrated model. The exchange coupling constants J1 (ferromagnetic interaction) and J2 (antiferromagnetic interaction) both decrease smoothly with the increase of the doping level x, which is possibly related to the increase of lattice parameters. At the same time, the frustration parameter α=J2/J1 is unchanged, resulting in the unchanged temperatures corresponding to the maximum of magnetic susceptibility (TMax=40 K) and to the maximum probability of the magnetic transition (Th=24 K). It indicates th at α is the decisive factor for the frustrated systems.