We report neutron scattering measurements of the structure and magnetism of stage-4 ${\mathrm{La}}_2{\mathrm{CuO}}_{4+y}$ with $T_c\simeq 42\mathrm{K}.$ Our diffraction results on a single crystal sample demonstrate that the excess oxygen dopants form a three-dimensional ordered superlattice within the interstitial regions of the crystal. The oxygen superlattice becomes disordered above $T\simeq 330\mathrm{K},$ and a fast rate of cooling can freeze in the disordered-oxygen state. Hence, by controlling the cooling rate, the degree of dopant disorder in our ${\mathrm{La}}_2{\mathrm{CuO}}_{4+y}$ crystal can be varied. We find that a higher degree of quenched disorder reduces $T_c$ by $\sim 5\mathrm{K}$ relative to the ordered-oxygen state. At the same time, the quenched disorder enhances the spin-density wave order in a manner analogous to the effects of an applied magnetic field.

• Received 10 September 2003

DOI:https://doi.org/10.1103/PhysRevB.69.020502