Nuclear ground-state spin and magnetic moment of 21Mg

We present the results of combined laser spectroscopy and nuclear magnetic resonance studies of 21Mg. The nuclear ground-state spin was measured to be I = 5 / 2 with a magnetic moment of μ = − 0.983 ( 7 ) μ N . The isoscalar magnetic moment of the mirror pair ( F 21 , Mg 21 ) is evaluated and compared to the extreme single-particle prediction and to nuclear shell-model calculations. We determine an isoscalar spin expectation value of 〈 σ 〉 = 1.15 ( 2 ) , which is significantly greater than the empirical limit of unity given by the Schmidt values of the magnetic moments. Shell-model calculations taking into account isospin non-conserving effects, are in agreement with our experimental results.