The effect of graded anisotropy on static and dynamic magnetic properties of Ar+-irradiated FePt films has been investigated by static magnetometry, magnetic force microscopy, and Brillouin light scattering from thermally excited spin waves. A gradual variation of magnetic anisotropy with film thickness was obtained by Ar+ irradiation. The irradiation incidence angle influences the anisotropy profile: on decreasing α, a decreasing thickness of the hard L10 phase and an increasing thickness of the soft A1 phase were obtained. Accordingly, the zero-field spin-wave frequency gap was found to decrease. In the sample with the highest soft-phase thickness the spin-wave frequency gap takes a substantial value (ν0≈6 GHz), which could be reproduced assuming the presence of a nonzero "rotatable" anisotropy (i.e., any direction in the film plane can be established as the easy axis by the application of a saturating magnetic field along this direction). The hypothesis is supported by both magnetometry and magnetic force microscopy data.

Tunable spin-wave frequency gap in anisotropy-graded FePt films obtained by ion irradiation / Tacchi, S.; Pini, M. G.; Rettori, A.; Varvaro, G.; Di Bona, A.; Valeri, Sergio; Albertini, F.; Lupo, P.; Casoli, F.. - In: PHYSICAL REVIEW. B. - ISSN 2469-9950. - 94:2(2016), pp. 024432-1-024432-8. [10.1103/PhysRevB.94.024432]

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