Absence of stable collinear configurations in Ni(001) ultrathin films: Canted domain structure as ground state

Brillouin light scattering (BLS) measurements were performed for 17-120-Angstrom-thick Cu/Ni/Cu/Si(001) films. A monotonic dependence of the frequency of the uniform mode on an in-plane magnetic field H was observed both on increasing and on decreasing H in the range 2-14 kOe, suggesting the absence of a metastable collinear ground state. Further investigation by magneto-optical vector magnetometry in an unconventional canted-field geometry provided evidence for a domain structure where the magnetization is canted. Spin-wave calculations confirm the absence of stable collinear configurations.