Magnetic Phase Diagram and Superconductivity in High-Tc(La1-xBax)2CuO4

Abstract

The magnetic phase diagram of (La _{1- x} Ba _x ) ₂ CuO ₄ has been studied using the ¹³⁹ La nuclear quadrupole resonance (NQR) technique. The ordering temperature T _N has been determined from the temperature dependence of the internal magnetic field at the La site proportional to the Cu magnetic moment. It has been found that T _N markedly decreases from T _N ∼240K for x =0, to 12K for x =0.008, however the magnitude of the Cu magnetic moment at 1.3 K is almost constant. On the other hand, in the composition range of 0.008< x T _N gradually decreases down to ∼1.5K for x =0.025 where the superconductivity appears. This demonstrates that two-dimensional correlations within the CuO ₂ in-plane are quite strong. The magnetic phase diagram established from a microscopical point of view suggests a strong relationship between the antiferromagnetism and the superconductivity.