Tuning of perpendicular magnetic anisotropy in Bi-substituted yttrium iron garnet films by He+ ion irradiation

We report the continuous tuning of magnetic anisotropy in perpendicularly magnetized bismuth-substituted yttrium iron garnet (Bi-YIG) films via He+ ion irradiation. Our findings indicate that the magnetization direction of epitaxial Bi-YIG films on sGGG substrates transitions from out of plane in the as-grown state to in plane after He+ ion irradiation at a fluence exceeding 2×1014ions/cm2. The reorientation is attributed to the relaxation of tensile film strain, which reduces the perpendicular magnetic anisotropy without affecting the saturation magnetization. The Gilbert damping parameter and the inhomogeneous broadening of the ferromagnetic resonance linewidth show only minimal increases with ion irradiation. Additionally, at a fluence of 5×1013ions/cm2, we observe the formation of magnetic bubble domains in the Bi-YIG films. Micromagnetic simulations estimate a Dzyaloshinskii-Moriya interaction of 0.006mJ/m2, which is insufficient for stabilizing Néel-type skyrmions. Finally, we demonstrate that the effects of He+ ion irradiation can be largely reversed through thermal annealing in an oxygen atmosphere.