Decomposition of the spin-1/2 Heisenberg chain compound Sr2CuO3 in air and water: An EPR and magnetic susceptibility study of Sr2Cu(OH)6

The reaction of Sr2CuO3 with air and liquid water was studied to address the origin of the reported variable Curie-Weiss impurity contribution to the magnetic susceptibility X of this compound at low temperatures. Sr2CuO3 was found to decompose upon exposure to either of these environments. The compound Sr2Cu(OH)6 was identified as the primary reaction product. A pure sample of Sr2Cu(OH)6 was then prepared separately. Electron paramagnetic resonance (EPR), isothermal magnetization versus magnetic field M(H) and X versus temperature T measurements demonstrate that Sr2Cu(OH)6 contains weakly interacting Cu+2 magnetic moments with spin S = 1/2 and average g-factor 2.133. From a fit of X(T) by the Curie-Weiss law and of the M(H) isotherms by modified Brillouin functions, the exchange interaction between adjacent Cu+2 spins was found to be J/kB = -1.06(4)K, a weakly antiferromagnetic interaction. Our results indicate that the previously reported, strongly sample-dependent, Curie-Weiss contribution to X(T) of a polycrystalline Sr2CuO3 sample most likely arises from exposing the sample to air, resulting in a variable amount of paramagnetic Sr2Cu(OH)6 on the surface of the sample.