Magnetic Susceptibility of YBa₂(Cu_1-xFe_x)₃O_y Prepared by Various Heat Treatments

The magnetic susceptibility was measured for YBa₂(Cu_1-xFe_x)₃O_y (0≦x≦0.10) prepared by the `usual' and `special' heat treatments. By the special heat treatment, we mean that the sample prepared by the usual method was reduced at 800°C in flowing N₂ gas followed by reoxidation in flowing O₂ gas below 400°C, stabilizing the orthorhombic phase to higher Fe concentrations. We estimated the effective magnetic moment per Fe in the Cu1 site, P_eff(1), from the magnetic susceptibility combined with the result of the Mössbauer effect measurement. The values of P_eff(1) could be calculated as 4.4 µ_B and 2.2 µ_B for the compounds with the `usual' and the `special' heat treatments, respectively. This smaller P_eff(1) may be attributed to the antiferromagnetic coupling between Fe spins within the process at high temperature.