  Ferromagnetism emerges when the Moire superlattice formed by stacking two
graphene monolayers in a magic twist angle are filled with integer number
electrons. This work investigates the ferromagnetism based on the Ising models
for a triangular lattice at one-quarter filling, a square lattice at half
filling and a Kagome lattice at three-quarters filling of electrons. The
temperature dependent heat capacity, magnetic susceptibility, energy and
magnetization curves are calculated at zero magnetic field with a Monte Carlo
method, leading to derive the phase transition temperatures, T_c=0.76, 1.33 and
4.75 K, respectively. Magnetization curves at finite magnetic field show strong
hysteresis at temperature below 0.5 K for all the fillings considered,
indicating the ferromagnetism of the system; the results are in agreement with
experimental observations.
