The spin magnetic-dipole transitions and the neutron-proton spin-spin correlations in $sd$-shell even-even nuclei with $N=Z$ are investigated by using shell-model wave functions taking into account enhanced isoscalar (IS) spin-triplet pairing as well as the effective spin operators. It was shown that the IS pairing and the effective spin operators gives a large quenching effect on the isovector (IV) spin transitions to be consistent with data observed by $(p,p^{\prime })$ experiments. On the other hand, the observed IS spin strengths show much smaller quenching effect than expected by the calculated results. The IS pairing gives a substantial quenching effect on the spin magnetic-dipole transitions, especially on the IV transitions. Consequently, an enhanced IS spin-triplet pairing interaction enlarges the proton-neutron spin-spin correlation deduced from the difference between the IS and the IV sum-rule strengths. The $\beta$-decay rates and the IS magnetic moments of the $sd$ shell are also studied in terms of the IS pairing as well as the effective spin operators.

• Received 26 July 2017
• Revised 25 March 2018

DOI:https://doi.org/10.1103/PhysRevC.97.054333