We present zero-field muon spin relaxation (μSR) measurements of ${\mathrm{La}}_{1.6-x}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ with $x=0.125,0.15,0.2;{\mathrm{La}}_{1.475}{\mathrm{Nd}}_{0.4}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_4,{\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_4,$ and ${\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125-y}{\mathrm{Sr}}_y{\mathrm{CuO}}_4$ with $y=0.025,\mathrm{0.065.}\mathrm{}$ All of the samples with dopant concentrations $x+y<~0.15$ show similar static magnetic order with coherent precession of the muon spins below $T_N\approx 30\mathrm{K},$ with a $\overrightarrow{T}0$ ordered Cu moment $\approx 0.3{\mu }_B.$ The samples with $x=0.20\mathrm{}$ show no coherent precession but manifest two distinct relaxation regimes, typical of quasistatic magnetism. We then present transverse-field μSR hysteresis measurements of the ${\mathrm{La}}_{1.45}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_4$ and ${\mathrm{La}}_{1.4}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{0.2}{\mathrm{CuO}}_4$ systems that show a large superconducting response below approximately 7 K and 12 K, respectively. We argue that superconductivity and magnetic order coexist in the $x=0.15\mathrm{}$ system.

• Received 23 April 1998

DOI:https://doi.org/10.1103/PhysRevB.58.8760