Thermodynamic properties in the approach to the quantum critical point of the spin-ladder material Na2Co2(C2O4)3(H2O)2 -: art. no. 087204

Magnetic susceptibility and heat capacity measurements as a function of temperature on a single-crystal sample of a spin-ladder material, Na2Co2(C2O4)(3)(H2O)(2), are reported. Principal susceptibilities, parallel and perpendicular to the ladder direction, respectively, show broad maxima around 22 and 17 K. Both susceptibilities decay exponentially down to about 5 K and thereafter they are essentially independent of temperature. These findings amount to a signature of a quantum phase transition from a spin-liquid to Neel ordered state previously predicted theoretically. No anomaly is found in the heat capacity around the transition temperature.