Chiral morphology in ferrimagnetic Pt/Co/Tb bubble domains

Abstract

The Dzyaloshinskii-Moriya interaction (DMI) is a key factor in chiral spin textures and has great potential in spintronics-based applications. The asymmetric bubble domain expansion under an in-plane magnetic field is a common method for DMI evaluation. However, abnormal bubble expansions occur occasionally in the creep regime, which may lead to deviations in the DMI evaluation, implying various physical phenomena in domain wall (DW) kinetics. In this study, DMI evaluation of ferrimagnetic Pt/Co/Tb trilayers was conducted via DW motion in the creep and flow regimes, where the in-plane fields of minimum DW velocities are significantly different for 1.5 nm Co. The accuracy of the extracted DMI effective field in the flow regime was confirmed by Brillouin light scattering measurements, where the DMI coefficient was approximately $1\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$. In the creep regime, a typical flattened bubble shape was observed; accordingly, the dominant direction of the DW motion velocity changes with increasing the in-plane magnetic fields. Based on the bubble morphology and DW anisotropy energy analyses, we attributed the bubble expansion phenomena in the creep regime to the vertical Bloch lines. Our study provides alternatives for a better understanding of DW kinetics in DMI evaluations, which is essential for spin-texture applications.