In two-dimensional (2D) ferromagnets, anisotropy is essential for the magnetic ordering as dictated by the Mermin-Wagner theorem. The recently discovered van der Waals ferromagnets are largely considered to have uniaxial anisotropy. On the other hand, honeycomb lattice is immune to magnetic frustration even with antiferromagnetic exchange coupling due to its bi-partite unit cell.
Click here for original story, Frustrated ferromagnetic transition in AB-stacked honeycomb bilayer
Source: Phys.org