Control of interlayer friction in two-dimensional ferromagnetic CrBr₃

Two-dimensional (2D) magnetic materials may offer new opportunities in the field of lubrication at the nanoscale. It is essential to investigate the interfacial properties, particularly magnetic coupling, at the interfaces of 2D magnetic materials from the point of view of friction. In the present study, we investigated the tribological and interfacial properties at the interface of bilayer CrBr₃ by performing first-principles calculations. The effects of normal load, biaxial strain and carrier doping on interlayer magnetic coupling were also studied. Our calculations identify the ferromagnetic (FM)-antiferromagnetic (AFM) conversion of the interlayer magnetic couplings, which leads to the reduction of the sliding energy barriers. Importantly, our calculations demonstrate the lower sliding energy barrier at the interface of 2D FM CrBr₃, implying lower friction and better lubricating properties. Additionally, we found that a normal load of 0.5-1.0 eV Å^-1, a biaxial compressive strain of 0% to -5%, and a carrier doping of -0.2 to 0.2 e f.u.^-1 are effective in reducing the sliding energy barrier and the friction. It is also found that the biaxial strain tunes the interlayer electron redistribution and thus alters the interlayer interaction and friction. The differences between the lubricating properties of 2D magnetic CrX₃ (X = Cl, Br and I) have also been studied. The present findings are inspiring for the application of 2D magnetic materials as solid lubricants in the fields of lubrication at the nanoscale.