  We investigate the magnetic dipole moments in even-even self-conjugate nuclei
from ${}^{12}\mathrm{C}$ to ${}^{44}\mathrm{Ti}$. For the latter, the measured
gyromagnetic factors of excited states turn out to assume the same value of $g
\approx + 0.5$ within statistical errors. This peculiar feature can be
interpreted on the basis of collective excitations of $\alpha$-clusters.
Analogously, the behaviour of the same observable is studied for all isotopes
obtained by adding one or two neutrons to the considered self-conjugate nuclei.
It is found that for the $N = Z + 1$ isotopes the $\alpha$-cluster structure
hardly contributes to the observed negative g- factor value, corroborating
molecular $\alpha$-cluster models. The addition of a further neutron, however,
restores the original $\alpha$-cluster g-factors, except for the semi-magic
isotopes, in which the deviations from $g \approx + 0.5$ can be associated with
the relevant shell closures. Secondly, we analyze the same observable in the
framework of a macroscopic $\alpha$-cluster model on a finite lattice of side
length $L$. We focus on the discretization effects induced in the magnetic
dipole moments of the $2_1^+$ and the $3_1^-$ states of ${}^{12}\mathrm{C}$ at
different values of the lattice spacing $a$.
