Prediction of carbon-based metal-free compounds with antiferromagnetism and superhardness

Magnetic superhard materials are still scarce, although they are very important to magnetic devices in extreme environment. Here, we predict a series of antiferromagnetic carbon-based compounds through stacking diamane and 2D C ₄N ₃ . The result exhibits that all the ground states of these compounds display antiferromagnetic ordering and superhard nature. The antiferromagnetism originates from the unpaired electrons of the low-coordinated C atoms at the interface. Interestingly, their hardness, magnetic moment, dynamic and mechanical stabilities are independent of the stacking sequence of the two precursors. The Vickers hardness is ∼ 70 GPa given by Chen model, the magnetic moment is ∼ 0 . 44 μ B . Notably, the magnetic moment is insensitive to the external pressure, whereas the magnetic transition temperature would increase with increasing the external pressure. On the contrary, the electronic property is strongly dependent on the stacking sequence, resulting in energy gaps ranging from 1.00 to 1.30 eV, despite all behaving as semiconductors. This work opens a potential way to design magnetic carbon-based materials with superhard feature.