Magnetic dipole excitations in magic nuclei with subtracted second random-phase approximation

Magnetic dipole (M1) excitations of magic nuclei ⁴⁸Ca, ⁹⁰Zr, and ¹³²Sn are investigated by a self-consistent Hartree-Fock (HF) plus subtracted second random-phase approximation (SSRPA) with Skyrme energy density functions (EDFs). We clarify the effects of the mixing of two-particle two-hole (2p-2h) configurations and tensor correlations in SSRPA on the excitation energies and the quenching of the $M1$ strength. It is shown that the 2p-2h configurations shift the $M1$ peak energies downwards by about 1.5 MeV in both ⁴⁸Ca and ⁹⁰Zr. In contrast, the tensor correlations move the peaks upwards and improve the description of experimental data. We also show that the 2p-2h configurations largely fragment the $M1$ strength, and reduce the cumulative strengths around the main $M1$ peaks by about 25% and 27% in ⁴⁸Ca and ⁹⁰Zr, respectively, compared with those of random-phase approximation (RPA), as an outcome of the combined effect with the tensor force. The $M1$ transitions in ¹³²Sn are calculated by the same SSRPA model with the Skyrme EDF including the tensor terms.