Muon spin relaxation study of the stripe phase order in La1.6-xNd0.4SrxCuO4 and related 214 cuprates

We present zero-field muon spin relaxation (μSR) measurements of La_1.6-xNd_0.4Sr_xCuO₄ with x=0.125,0.15,0.2; La_1.475Nd_0.4Ba_0.125CuO₄, La_1.875Ba_0.125CuO₄, and La_1.875Ba_0.125-ySr_yCuO₄ with y=0.025,0.065. 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~30 K, with a T-->0 ordered Cu moment ~0.3μ_B. The samples with x=0.20 show no coherent precession but manifest two distinct relaxation regimes, typical of quasistatic magnetism. We then present transverse-field μSR hysteresis measurements of the La_1.45Nd_0.4Sr_0.15CuO₄ and La_1.4Nd_0.4Sr_0.2CuO₄ 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 system.