Resistivity, magnetic-susceptibility, and specific-heat studies ofErBa2(Cu(1−x)Mx)3O7−y[(M=Ni, Zn, Fe, Co, and Ga) andx=0.005]: The effect of site-dependent substitutional disorder

We report here a systematic study of the resistivity, ac magnetic susceptibility, and specific-heat (${\mathit{C}}_{\mathit{p}}$) anomalies in Er-1-2-3 systems for both the pure phase and when Cu is partly (0.5%) replaced by Ni, Zn, Fe, Co, and Ga. These substitutions are aimed at studying the role of site-dependent in-plane and out-of-plane disorder, in conjunction with fluctuation effects. Analysis of the results shows that, as compared to in-plane, the out-of-plane substitutions exhibit a domination of the fluctuation effect. This has been explained from the fact that the out-of-plane disorder substantially decouples the interlayer links between ${\mathrm{CuO}}_{2}$ planes across the adjoining unit cells. This transforms the system to be more two dimensional, thereby enhancing the contribution of fluctuations.