Abstract
Magnetic susceptibility, magnetization and heat capacity measurements are made on a single crystal sample of a spin–ladder material, Na2Fe2(C2O4)3(H2O)2. The susceptibilities show a broad maximum at a temperature of about 25 K and 20 K parallel (χ||) and perpendicular (χ⊥) to the ladder direction, respectively. The maximum value of χ|| is about three times larger than that of χ⊥. Both χ|| and χ⊥ decrease steeply at low temperatures down to about 5 K, at which χ|| shows an upturn. We find a broad peak in the temperature dependence of the heat capacity. Susceptibility, magnetization and heat capacity data are used to construct the magnetic field versus temperature phase diagram of this compound. Quantum fluctuations are not strong enough to form a singlet ground-state, probably due to the presence of Ising anisotropy. The actual ground state is expected to be close to the quantum critical-point between the spin-gapped and a Néel ordered phases with the help of the inter-ladder interaction.
