Magnetic multilayers are material systems that offer a high degree of tunability with respect to their magnetic and electronic properties. These are essential for today’s spintronics and magnonics-based magnetic applications 1, 2. The Dzyaloshinskii-Moriya interaction (DMI) 3 is one of the interesting phenomena in such multilayers that give rise to the presence of magnetic skyrmions under certain conditions even at room temperature. Pt/Co is one of the most promising classes of the multilayers that contributes to a significant DMI due to the different characters of Pt/Co and Co/Pt interfaces 4. The performance of the films may vary depending on the substrates, deposition temperature, layer thickness, and other factors in the Pt/Co multilayers. The thermal stability can be significantly increased and the magnetic anisotropy of Pt/Co multilayers can be controlled by adding spacer layers between two Co layers 5. In our study, we investigate magnetic bubbles in Pt/Co-based multilayer thin films. The bubbles have been expanded using an external magnetic field both in-plane and out-of-plane. In presence of the in-plane field, bubbles expand asymmetrically as observed in Fig.1(a). The in-plane field-dependent velocities of two opposite chiral domain walls are measured as shown in Fig. 1(b). The asymmetry of bubble expansion is found to be influenced by the thickness of Co which gives us information about the intrinsic chiral properties of the system. Mumax simulations are performed to understand underlying behavior. The study is important for race track memory applications.

References
1. R. E. Camley, and R. L. Stamps, “Magnetic multilayers: spin configurations, excitations, and giant magnetoresistance,” Journal of Physics: Condensed Matter, vol. 5, no. 23, 1993. 2. E. Y. Vedmedenko, R. K. Kawakami, D. D. Sheka, P. Gambardella, A. Kirilyukand, A. Hirohata, C. Binek, O. Chubykalo-Fesenko, S. Sanvito, and B. J. Kirby, “The 2020 magnetism roadmap,” Journal of Physics D: Applied Physics, vol. 53, no. 45, 2020. 3. T. Moriya, “Anisotropic Superexchange Interaction and Weak Ferromagnetism,” Phys. Rev, 1960. 4. A. W. J. Wells, P. M. Shepley, C. H. Marrows, and T. A. Moore, “Effect of interfacial intermixing on the Dzyaloshinskii-Moriya interaction in Pt/Co/Pt,” Phys. Rev. B, vol. 95, 2017. 5. S. Eimer, H. Cheng, J. Li, and X. Zhang, “Perpendicular magnetic anisotropy based spintronics devices in Pt/Co stacks under different hard and flexible substrates,” Science China. Information Sciences, 2021.