Magnetic Susceptibility of YBa₂Cu₃O7-xwith Various Oxygen Deficiency

The magnetic susceptibility of YBa 2 Cu 3 O 7- x with various oxygen deficiency (0< x <0.9) was measured below room temperature. The susceptibility of samples in orthorombic phase (0< x <0.44) shows the linear temperature dependence, χ 0 + A T , with diamagnetic deviation due to the superconducting fluctuation above the T c , without any upturn with decreasing temperature. χ 0 decreases linearly from 5.0×10 -7 to 2.2×10 -7 emu/g, and the linear slope A increases from 0 to 5.6×10 -10 emu/gK with increasing x , although the T c changes from 90 K to 60 K rather discontinuously in this phase. In tetragonal phase samples (0.5< x <0.7), an upturn in the susceptibility with decreasing temperature was inevitably observed, suggesting the appearence of localized magnetic moments which were also detected by EPR. A new analysis of subtracting the extrinsic magnetic contribution which is proportional to T -4/3 from the observed static susceptibility is proposed with the aid of EPR results.