Effect of a magnetic field on long-range magnetic order in stage-4 and stage-6 superconducting La2CuO4+y -: art. no. 054501

We have measured the enhancement of the static incommensurate spin-density wave (SDW) order by an applied magnetic field in stage-4 and stage-6 samples of superconducting La2CuO4+y. We show that the stage-6 La2CuO4+y (T-c=32 K) forms static long-range SDW order with the same wave vector as that in the previously studied stage-4 material. We have measured the field dependence of the SDW magnetic Bragg peaks in both stage-4 and stage-6 materials at fields up to 14.5 T. A recent model of competing SDW order and superconductivity describes these data well.