Magnetic field induced chirality in Ho/Y multilayers with gradually decreasing anisotropy

Metal rare-earth magnetic/nonmagnetic Ho/Y superlattice structures possess a coherent spin helix propagating through many superlattice layer repetitions. An external magnetic field applied in the film plane induces a nonzero average chirality of the helices. It is shown that the direction of the applied in-plane field can modify the value and sign of the chirality parameter $\ensuremath{\gamma}$. The dependence of $\ensuremath{\gamma}$ on the relative angle of applied field during the field-cooling procedure has an oscillatory character and can be described by simple sinusoidal function with \ensuremath{\pi} periodicity. The experimental finding is discussed from the point of view of an interbalance between Zeeman energy, magnetocrystalline anisotropy, and induced uniaxial anisotropy.