Magnetic Force Microscopy and Brillouin Light Scattering study of magnetostrictive Fe0.8Ga0.2 film with stripe domains

We report on Magnetic Force Microscopy (MFM) and Brillouin Light Scattering (BLS) investigation of magnetostrictive Fe0.8 Ga0.2 film with thickness of 72 nm, grown by molecular beam epitaxy onto ZnSe/GaAs(001) substrate. [1] When the external magnetic field, applied in the sample plane, is reduced below about 2 kOe, we observed the formation of stripe domains aligned along the direction of the magnetic field and with a perpendicular component of the magnetization pointing alternately up and down (with respect to the film surface). This is caused by the competition between the easy-plane dipolar interaction and the out-of-plane magnetic anisotropy, induced by magnetostriction. MFM measurements showed that the stripes direction can be rotated applying a magnetic field of increasing intensity in a direction perpendicular to the stripes axis. For H=800 Oe the stripes rotation was completed, and when the field was removed the stripe structure was preserved. BLS measurements were performed at remanence rotating the sample around the film normal, when the stripes are prepared along the [110] direction. We observed two perpendicular standing modes having a constant frequency, and a Damon-Eshabach (DE) like mode which exhibits a pseudo-uniaxial anisotropy showing a frequency maximum in correspondence to the perpendicular orientation between the in-plane transferred wave-vector and the stripes axis (Fig.1). The values of the frequency of the DE-like mode were fitted (continuous curve) by means of an analytic equation including a rotatable field (Hrot ~ 1 kOe) associated with the presence of the stripe pattern. Moreover, from a fit of the DE-like mode versus the intensity H of the inplane applied magnetic field, we found that, in contrast with an usual uniaxial anisotropy field, the value of Hrot decreases with increasing H and vanishes when the magnetization lies entirely in plane. [1] M. Eddrief et al. Phys. Rev. B, 84, 161410 (2011)