  We have measured the effect of a c-axis aligned magnetic field on the
long-range magnetic order of insulating Nd2CuO4, as-grown nonsuperconducting
and superconducting Nd1.85Ce0.15CuO4. On cooling from room temperature, Nd2CuO4
goes through a series of antiferromagnetic (AF) phase transitions with
different noncollinear spin structures. In all phases of Nd2CuO4, we find that
the applied c-axis field induces a canting of the AF order but does not alter
the basic zero-field noncollinear spin structures. Similar behavior is also
found in as-grown nonsuperconducting Nd1.85Ce0.15CuO4. These results contrast
dramatically with those of superconducting Nd1.85Ce0.15CuO4, where a c-axis
aligned magnetic field induces a static, anomalously conducting, long-range
ordered AF state. We confirm that the annealing process necessary to make
superconducting Nd1.85Ce0.15CuO4 also induces epitaxial, three-dimensional
long-range ordered cubic (Nd,Ce)2O3 as an impurity phase. In addition, the
annealing process makes a series of quasi two-dimensional superlattice
reflections associated with lattice distortions of Nd1.85Ce0.15CuO4 in the CuO2
plane. While the application of a magnetic field will induce a net moment in
the impurity phase, we determine its magnitude and eliminate this as a
possibility for the observed magnetic field-induced effect in superconducting
Nd1.85Ce0.15CuO4.
