  Magnetic dipole (M1) excitation is the leading mode of multi-nucleon
excitations induced by the magnetic field, and is a phenomenon of the
spin-orbit (SO) splitting and residual interactions involved. In this work, we
investigate the effects of the residual interactions on the M1 excitation from
a novel perspective, the framework of relativistic nuclear energy-density
functional (RNEDF). The relativistic Hartree-Bogoliubov (RHB) model is utilized
to determine the nuclear ground state properties, while the relativistic
quasi-particle random-phase approximation (RQRPA) is employed for the
description of M1-excitation properties. From the analysis of M1 mode in the Ca
isotope chain, role of the isovector-pseudovector (IV-PV) residual interaction
is discussed. For open-shell nuclei, the pairing correlation also plays a
noticeable role in the M1 mode. The experimental data on M1 mode is expected to
provide a suitable reference to improve and optimize the theoretical aspects to
describe the residual interactions.
