Muon spin relaxation study of 1/8 anomaly in high-Tc superconductor La2-x-yEuySrxCuO4

In order to investigate the origin of the so-called 1/8-anomaly in high-T-c La(Sr,Ba)-214, we have carried out the measurements of electric resistivity, magnetic susceptibility and muon spin relaxation (mu SR) for the samples La2-x-yEuySrxCuO4. Eu(y=0.1)-substitution stabilizes a low temperature tetragonal (LTT) phase and consequently, around x=0.125 (1/8) the magnetic ordering temperature T. shows the maximum value while the superconducting critical temperature T. is most suppressed, indicating a strong competition between them, and over the whole x range T-c are entirely lowered. On the other hand, with increasing y up to y similar to 0.05 at x=0.125 (1/8), T-m steeply increases and Tc rapidly decreases, indicating transition to LTT, but both the temperatures gradually decrease in LTT phase above y similar to 0.05. In all Eu-substituted samples, the resisitivity upturn is observed at low temperature, implying carrier localization. The anomalous suppression of T-c in Eu-substituted LSCO can be attributed to the strong carrier localization in LTT phase and the subsequent peculiar magnetic order such as spin and charge stripe-order.