Magnetic anisotropies and stripes rotation in FeGa thin films studied by magnetic force microscopy and Brillouin light scattering

Galfenol alloys Fe1-xGax exhibit a strong magnetostriction, whose size is very sensitive to Ga concentration [1]. In this work, we have studied the magnetic properties of Fe1-xGax epitaxial films deposited onto ZnSe/GaAs (100) as a function of both the film thickness and the Ga concentration, by means of Brillouin Ligth Scattering (BLS) and Magnetic Force Microscopy (MFM). Thinnest films show an in-plane magnetic anisotropy resulting from the superposition of a biaxial term, typical of the bulk Fe, and a uniaxial anisotropy with the easy axis along the [1-10] direction. We found the intensity of the in-plane anisotropy decreases on increasing both the film thickness and the Ga concentration. In particular, for a Fe0.80Ga0.20 72 nm thick we observed an in-plane isotropic behaviour. MFM measurements have pointed out the presence of stripe domain patterns at remanence for films with Gallium concentration greater than 14% and a thickness of 72 nm. In-field MFM has been employed to perform experiments of domains rotation: after the induction of stripes by the application of a field (up to 3 kOe) along a preferred orientation of the crystal, the rotation process has been produced by the application of another field placed at 45 or 90 degrees from the first one and followed by detecting the MFM signal at different field intensities. Depending on the specific orientations considered, we have observed coherent rotation of linear stripes together with transitions from stripes to labyrinth domain patterns or saw-tooth zig-zag periodic patterns. The stripes period was on the average of 120 nm. In any case, the stripes maintained the direction of the external applied field, even after field removal. This effect is known as rotatable anisotropy and is a consequence of magnetostriction. [1] M. Eddrief et al., Phys. Rev. B 84, 161410 (2011