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

TL;DR

This study combines experimental Brillouin Light Scattering measurements and theoretical modeling to reveal the coexistence of two spin-wave modes in ultrathin Fe/GaAs(001) films below a critical magnetic field, linked to a non-homogeneous magnetic ground state.

Contribution

It introduces a model explaining the double-peaked BLS spectra through perpendicular stripe domains and confirms the existence of two spin-wave modes in ultrathin Fe films.

Findings

Observation of double-peaked BLS spectra below critical field

Theoretical model supports non-homogeneous ground state with stripe domains

Agreement between calculated and experimental spin-wave frequencies

Abstract

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