Effect of a magnetic field on long-range magnetic order in stage-4 and   stage-6 superconducting La2CuO(4+y)
  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 La2CuO(4+y). We show that the stage-6 La2CuO(4+y) (Tc=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. 
B. Khaykovich, R. J. Birgeneau, F. C. Chou, R. W. Erwin, M. A.   Kastner, S.-H. Lee, Y. S. Lee, P. Smeibidl, P. Vorderwisch,...