$M1\mathrm{}$ spin excitations in deformed nuclei within a microscopic multiphonon approach

We adopt the quasiparticle-phonon nuclear model to compute the $M1\mathrm{}$ strength distribution in the energy range 4–10 MeV in the deformed ${}^{154}\mathrm{Sm}.$ We show that the coupling with two-phonon configurations enhances considerably the fragmentation of the $M1\mathrm{}$ strength with respect to the random-phase approximation but not enough to reach a complete agreement with experiments. The results obtained contribute also to shed light on the controversial properties of the $M1\mathrm{}$ spectrum in this energy range.