Behavior of Helical Spin Structures in Applied Magnetic Fields

The problem of the behavior of helical spin structures and the phase transitions they exhibit in applied magnetic fields is studied theoretically. We have obtained a numerical solution valid for the planar helix at $T=0\mathrm{}$ °K with an arbitrary number of interplanar exchange interactions, an arbitrary form of in-plane anisotropy, and an external magnetic field applied in the plane. We calculated the phase diagram for the case of two interplanar exchange constants and no anisotropy, and found different behavior in the intermediate field region from that predicted by the previous theory. As a new result, in the case of an in-plane anisotropy, the angle dependence of the transition fields has been obtained.