Abstract
The phase diagram of the title system is remarkably rich, exhibiting regions of long-range antiferromagnetic order, short-range (spin-glass-like) order, high temperature superconductivity, or none of these. Here, the phase diagram is reviewed, with an emphasis on our recent studies using
139La NQR, powder and single crystal neutron diffraction, and magnetization measurements for 0≤
χ≤0.15 and 0≤
δ≤0.1.