Simultaneous existence of two spin-wave modes in ultrathin Fe/GaAs(001) films studied by Brillouin Light Scattering: experiment and theory

摘要

A double-peaked structure was observed in the {\it in-situ} Brillouin LightScattering (BLS) spectra of a 6 \AA$ $ thick epitaxial Fe/GaAs(001) film forvalues of an external magnetic field $H$, applied along the hard in planedirection, lower than a critical value $H_c\simeq 0.9$ kOe. This experimentalfinding is theoretically interpreted in terms of a model which assumes anon-homogeneous magnetic ground state characterized by the presence ofperperpendicular up/down stripe domains. For such a ground state, two spin-wavemodes, namely an acoustic and an optic mode, can exist. Upon increasing thefield the magnetization tilts in the film plane, and for $H \ge H_{c}$ theground state is homogeneous, thus allowing the existence of just a singlespin-wave mode. The frequencies of the two spin-wave modes were calculated andsuccessfully compared with the experimental data. The field dependence of theintensities of the corresponding two peaks that are present in the BLS spectrawas also estimated, providing further support to the above-mentionedinterpretation.