Chiral Inversion of Resonant Modes in Gd_xFe_1-x Ferrimagnetic Alloy

Antiferromagnetic materials exhibit higher frequencies (up to THz) compared to ferromagnetic materials and demonstrate better magnetic field stability due to the absence of stray fields. They possess a twin sublattice structure, and their intrinsic magnetic excitation modes exhibit both left-handed and right-handed precession modes. However, controlling their magnetic order with an external magnetic field is challenging as their net magnetic moment is zero. In contrast, ferrimagnetic materials, with a twin sublattice structure and partial net magnetic moment, provide a suitable platform for studying antiferromagnetic spin dynamics. In ferrimagnetic alloys with specific composition ratios, compensation temperatures for magnetic moment and angular momentum exist due to thermal excitation. Moreover, as the composition ratio changes, points of magnetic moment compensation (PM) and angular momentum compensation (PA) are observed. In this study, we employed atomic-scale micromagnetic simulation techniques considering the lattice spatial structure to investigate the chirality reversal characteristics of GdxFe1-x ferrimagnetic alloys at different composition ratios and the variations of spin wave precession near the PA point under an external magnetic field. Our results indicate that the chirality of the resonant mode in GdxFe1-x alloys undergoes reversal with an increase in Gd ratio. Additionally, the energy degeneracy points of the two resonant modes deviate from zero magnetic field, distinguishing them from antiferromagnetic materials, owing to the different saturation magnetization strengths of the two sublattices in GdxFe1-x alloys. That is to say, the chirality of the spin resonance mode changes with variations in the external magnetic field under the same composition ratio. We also provide a theoretical explanation for this phenomenon.