Abstract
Insulating Bi 2 Sr 2 CoO 6+δ is nearly isomorphic with the Bi(2201)-type high-T c superconductors. Magnetic and calorimetric studies were carried out on single crystal samples of this layered compound. Based on magnetic measurements, the cobalt ions undergo a canted antiferromagnetic ordering at T N =159 K. A low temperature neutron diffraction study of the magnetic structure is in progress. The molar magnetic susceptibility χ ab (H⊥c) above 200 K can be well fitted by the Curie-Weiss form χ ab (T)=χ 0 +C/(T-θ p ), with χ 0 =0.56 cm 3 /mol, Curie constant C=3.2×10 -2 cm 3 K/mol and Curie-Weiss intercept θ p =159 K. There is no magnetic specific heat peak, however, prevailing around T N . This anomalous calorimetric behavior is attributed to the two-dimensional quantum spin fluctuation of Co spins above T N in the layered compound as previously observed for Cu spins in (Gd 1.85 Ce 0.15 )CuO 4-δ and La 2 CuO 4-δ . © 1993.