La1.8Sr0.2Ni1-xCuxO4+δ, (0≤x≤0.9): magnetization measurements

Oxides with the general formula La1.8Sr0.2Ni1-xCuxO4+δ, with 0≤x≤0.9, have been prepared as ceramic specimens. Structural studies have been carried out on the entire series. Heat capacity measurements have been carried out in the range 0.5 to 30 K. Magnetization measurements were made in the temperature region 4.2-300 K. None of the samples shows any indication of a transition to the superconducting state down to 4.2 K. Magnetization versus temperature curves do show a peak below 25 K; the peak becomes sharper and moves to lower temperatures with increasing x for x<0.8 and disappears for x≥0.8. The possible origin of the peak is discussed. (orig.)