Structural defects effect on ferromagnetism of layered oxysulfide (La1-xCaxO)Cu1-xNixS

We have studied the effect of structural defects on magnetic properties of (La1-xCaxO)Cu1-xNixS. The magnetization for samples containing less defects shows the magnetism consisting of a diamagnetism and a Pauli paramagnetism. Any ordered phase is not observed down to 2 K. A very weak ferromagnetic component is observed for non-stoichiometric system containing structural defects. These samples exhibit a well-defined hysteresis loop at room temperature. The Curie temperature obtained by the extrapolation of its temperature dependence increases with x. This ferromagnetism may be attributed to Ni and/or S related defects. (C) 2003 Elsevier Science B.V. All rights reserved.