Magnetic signatures on mixed-mode frequencies - I. An axisymmetric fossil field inside the core of red giantsL. Bugnet, V. Prat, S. Mathis, A. Astoul, K. Augustson, R. A. García, S. Mathur, L. Amard and C. NeinerA&A, 650 (2021) A53DOI: https://doi.org/10.1051/0004-6361/202039159