Evidence of successive magnetic transition in La2−xBaxCuO4. NQR studies of 139La

Nuclear quadrupole resonance (NQR) of 139 La has been performed to study the electronic and magnetic properties of La 2- x Ba x CuO 4 between 1.5 and 240 K. The temperature dependence of the separation of the double peaks in spectra clearly indicates the magnetic ordering in the small x region. The internal fields at La sites due to magnetic order largely decrease with Ba concentration. The divergence of 1/ T 2 indicates that another phase appears at low temperatures. The electric field gradient changes on passing from the normal to the superconducting states, indicating the apparent influence of superconductivity on the electronic state at La sites in this system.