Effect of Sn substitution for Cu on the magnetic and superconducting properties of La2-xSrx(Cu1-ySny)O4+δ (0 ≤ x ≤ 0.15)

We have investigated the effect of Sn doping on the magnetic and superconducting properties of La2-xSrx(Cu1-ySny)O4+δ with 0 ≤ x ≤ 0.15 and 0 ≤ y ≤ 0.01. Measurements of the 119Sn Moessbauer isomer shift of samples doped with y = 0.005 (119Sn) show that Sn is tetravalent (Sn4+) in the whole concentration range 0 ≤ x ≤ 0.15. On the other hand, the electrical resistivity, the Neel temperature (TN), and the superconducting temperature (Tc) are found to be affected by increasing the Sn content. In the anti-ferromagnetic state (x = 0.0.008), we find that TN is slightly affected by increasing Sn content. In the superconducting state (x = 0.065, 0.10 and 0.15), Tc is strongly suppressed with increasing Sn content. It is shown that the variation of TN upon Sn doping depends on the competition between two mechanisms: (1) magnetic disorder due to the nonmagnetic impurity which induces an uncompensated local magnetic moment on the CuO2 lattice and thereby tends to decrease TN; (2) reduction (compensation) of the number of the free O- holes by the excess electrons introduced by Sn4+ which leads to stabilizing the antiferromagnetic order and increasing TN. We further show that the suppression of Tc with increasing Sn content can be explained by the same magnetic mechanism (1) responsible for decreasing TN. (orig.)