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 (mu SR) measurements of La1 .6-xNd0.4SrxCuO4 with x = 0.125,0.15,0.2; La1.475Nd0.4Ba0.125CuO4, La1 .875Ba0.125CuO4, and La1.875Ba0.125-ySryCuO4 with y = 0.025,0.065. All of the samples with dopant concentrations x + y less than or equal to 0.15 show similar static magnetic order with coherent precession of t he muon spins below T-N approximate to 30 K, with a T-->0 ordered Cu m oment approximate to 0.3 mu(B). The samples with x=0.20 show no cohere nt precession but manifest two distinct relaxation regimes, typical of quasistatic magnetism. We then present transverse-field mu SR hystere sis measurements of the La1.45Nd0.4Sr0.15CuO4 and La1.4Nd0.4Sr0.2CuO4 systems that show a large superconducting response below approximately 7 K and 12 K, respectively. We argue that superconductivity and magne tic order coexist in the x=0.15 system.