  Using a tight-binding model along with the mean-field Hubbard method, we
investigate the effect of twisting angle on the magnetic properties of twisted
bilayer graphene (tBLG) quantum dots (QDs) with triangular shape and zigzag
edges. We consider such QDs in two configurations: when their initial untwisted
structure is a perfect AA- or AB-stacked BLG, referred to as AA- or AB-like
dots. We find that AA-like dots exhibit an antiferromagnetic spin polarization
for small twist angles, which transits to a ferromagnetic spin polarization
beyond a critical twisting angle $\theta_c$. Our analysis shows that $\theta_c$
decreases as the dot size increases, obeying a criterion, according to which
once the maximum energy difference between electron and hole edge states (in
the single-particle picture) is less than $(U / \gamma_0)\, t_0$, the
spin-polarized energy levels are aligned ferromagnetically [$U$ is the Hubbard
parameter and $\gamma_0$ ($t_0$) the graphene intralayer (interlayer) hopping].
Unlike AA-like dots, AB-like dots exhibit finite magnetization for any twist
angle. Furthermore, in the ferromagnetic polarization state, the ground net
spin for both dot configurations agrees with prediction from Lieb's theorem.
