  Metastable face-centered-cubic Fe78Ni22 thin films grown on Cu(001)
substrates are excellent candidates for focused ion beam direct writing of
magnonic structures due to their favorable magnetic properties after
ion-beam-induced transformation. The focused ion beam transforms the originally
nonmagnetic fcc phase into the ferromagnetic bcc phase with additional control
over the direction of uniaxial magnetic in-plane anisotropy. The
magnetocrystalline anisotropy in transformed areas is strong enough to
stabilize the magnetization in transverse direction to the long axis of narrow
waveguides. Therefore, it is possible to propagate spin waves in these
waveguides without the presence of an external magnetic field in the favorable
Demon-Eshbach geometry. Phase-resolved micro-focused Brillouin light scattering
yields the dispersion relation of these waveguides in zero as well as in
nonzero external magnetic fields.
