Quantum spin fluctuation in high Tc related systems

[[abstract]]In the insulating region of high-Tc related systems, antiferromagnetic ordering among Cu moments has often been observed by magnetic measurements or neutron diffraction. Calorimetric data for La2CuO4-δ and (Gd1.85Ce0.15)CuO4-δ, however, show no trace of the expected magnetic entropy Sm=Rln(2S+1)=Rln2 at the Neel temperature TN. Similar results even occur as the Co ions order in Bi2Sr2CoO6+δ, Co replacing for the two-dimensional dynamic short range ordering or quantum spin fluctuation persisting for above TN. The unusual behavior is apparently characteristic of the layered compounds as the consequence of a highly anisotropic coupling. With a strong exchange coupling J within the Cu-O or Co-O layer and a much weaker interlayer coupling J', two-dimensional dynamic short range ordering has gradually removed most of Sm as the temperature lowers toward TN, which reflects only the onset of a stabilized three-dimensionally ordered state[[fileno]]2010102010054[[department]]物理