Investigation of thermodynamic properties of Cu(NH3)4SO4·H2O, a Heisenberg spin chain compound

Detailed experimental investigation of thermal and magnetic properties are presented for Cu(NH3)4SO4·H2O, an ideal uniform Heisenberg spin ½ chain compound. A comparison of these properties with relevant spin models is also presented. Temperature dependent magnetic susceptibility and specific heat data have been compared with the exact solution for uniform Heisenberg chain model derived by means of Bethe ansatz technique. Magnetization isotherms measured as a function of field are analyzed using the numerical results simulated by Quantum Monte Carlo technique. Specific heat as a function of magnetic field (up to 7T) and temperature (down to 2 K) is reported. Subsequently, the data are compared with the corresponding theoretical curves for infinite Heisenberg spin ½ chain model with J = 6 K. Moreover, internal energy and entropy are calculated by analyzing the experimental specific heat data. Magnetic field and temperature dependent behavior of entropy and internal energy are in good agreement with the theoretical predictions.