The crystal structure and magnetic properties of Co(HPO3)⋅H2O have been determined. The solid crystallizes in space group Pca21, a=8.984(2) Å, b=7.918(2) Å, c=10.139(8) Å, V=721.2 Å3. Z=4 dcalc =2.89 g/cm3. The structure consists of layers only connected by hydrogen bonds. These layers can be viewed as formed by zigzag chains of edge‐sharing Co(II)O6 octahedra interconnected by a three atom bridge (O‐P‐O) and a single oxygen bridge. ac magnetic susceptibility measurements show a sharp peak at Tc =(10.8±0.1) K, and are consistent with a transition from one‐ to two‐dimensional magnetic order, in agreement with the structure. An analysis of the χT/C vs ϵ=(1−Tc/T) data in the critical region, for T>Tc, using a double‐logarithmic plot, yields a critical exponent γ=1.75 for 0.01<ϵ<0.1, which correspond to a two‐dimensional Ising model.... [Leer más...]