Magnetic Properties of O2-Annealed YBa2(Cu1-xMx)3Oywith M=Fe, Co and Ni

The dc magnetic susceptibility of YBa 2 (Cu 1- x M x ) 3 O y with M=Fe and Co ( x <0.08) annealed in high-pressure oxygen gas was measured in the normal state. The annealing was done in flowing oxygen gas of about 6 kg/cm 2 for 24 hours at low temperatures (350–450°C) after an ordinary annealing in air. Although the O 2 annealing markedly enhances the superconducting transition temperature, the measured susceptibilities of Fe and Co substituents were essentially unchanged. The dc magnetic susceptibilities of the air- and O 2 -annealed samples with Ni ( x <0.08) were also measured and found to be the same. In this compound, the Ni atom was found to have a magnetic moment close to that of the Ni 2+ ion ( S =1, P eff =2.83 µ B ).