Magnetic field-induced change of modulated antiferromagnetic correlations for La_1.85 Sr_0.15 Cu_{1 - y} Zn_y O₄ with y = 0.004, 0.02

In the high temperature superconductor La_1.85 Sr_0.15 Cu_{1 - y} Zn_y O₄, we directly observed modulated antiferromagnetic correlations of Cu spin orientations via elastic (y = 0.02) and low energy inelastic (y = 0.004) magnetically scattered neutron intensity. A magnetic field was applied perpendicular to the CuO₂ plane to change these correlations. For y = 0.02 we confirmed an earlier observation of elastic scattered intensity at 2 K and 0 T. The component of the magnetic moment perpendicular to the scattering vector is μ_{⊥ Q} < 0.065 μ_B, and is enhanced by 32% when a 5.5 T field is applied. For y = 0.004, we observed a 145% enhancement of 3 meV spin excitations when a 14.5 T magnetic field is applied at 1.6 K. However, we observed no elastic scattered intensity at either 0 or 14.5 T.