Competition of Magnetic Order and Superconductivity in (La1-xBax)2CuO4 Systems

Abstract

Both the magnetic and superconducting properties of (La _{1- x} Ba _x ) ₂ CuO ₄ systems have been investigated in terms of ¹³⁹ La nuclear quadrupole resonance (NQR). For La ₂ CuO ₄ , it has clearly been demonstrated that the internal field H _n is applied on the La site by magnetic ordering below ∼240 K. The observed H _n is not consistently explained by the spin structure proposed in the neutron diffraction study. For the doped compound with x =0.01, the internal field at 1.3 K was almost the same as that for La ₂ CuO ₄ , while for x =0.025, it decreased and was significantly distributed. Furthermore, the superconductivity was found to set in around 2 K. From a microscopic point of view, it is concluded that the magnetic ordering and superconductivity compete around x =0.025.