New magnetic materials obtained by ion-exchange reactions from non-magnetic layered perovskites

New layered magnetic materials, (MCl)Ca₂Ta₃O₁₀ (M = Cu, Fe), have been prepared by ion-exchange reactions of non-magnetic perovskite derivatives, ACa₂Ta₃O₁₀ (A = Rb, Li), in corresponding anhydrous molten salts. Powder x-ray diffraction patterns of the products are successfully indexed assuming tetragonal symmetry with cell dimensions a = 3.829 Å and c = 15.533 Å for Cu, and a = 3.822 Å and c = 15.672 Å for Fe. Being separated by the Ca₂Ta₃O₁₀ triple-layer perovskite slabs, the transition-metal chloride (MCl) network provides a two-dimensional magnetic lattice. Magnetic susceptibility measurements show that (CuCl)Ca₂Ta₃O₁₀ is in an antiferromagnetic state below 8 K, while (FeCl)Ca₂Ta₃O₁₀ has two anomalies at 91 and 125 K, suggesting successive phase transitions due to geometrical spin frustration.