Magnetic Properties of Superconducting and Nonsuperconducting GdBa₂(Cu_1−xM_x)₃O₇ (M=Fe, Co, Ni: x=0–0.19)

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Magnetization measurements were carried out for the samples of superconducting and nonsuperconducting GdBa₂(Cu_1−xM_x)₃O₇ (M=Fe, Co, Ni: x=0–0.19). From the magnetization curve at 1.3 K below Gd-ordering temperature T_N, a Gd-spin flipping field, a molecular field and an anisotropy field were determined to be 1.5 T, 3.0 T and 0.4 T, respectively, and decrease of their saturation magnetizations due to increase of dopants was also observed. Furthermore, it was found that T_N of metal doped samples decrease with increasing the concentrations of dopants. These results indicate that magnetic moments of doped metal atoms couple antiferromagnetically with Gd spins and this antiferromagnetic interaction reduces T_N of Gd spins.