First-principles study on ferromagnetism in W-doped graphene

Based on density-functional theory using the generalized gradient approximation plus Hubbard U scheme, we studied the structural, electronic, and magnetic properties of graphene doped with W atoms. Our results show that W introduces a spin polarized magnetic state with a local moment of 2.00 μ_B, which can be well understood using a hybridization model. When two W defects are introduced into graphene, the ferromagnetic (FM), antiferromagnetic, and paramagnetic states are obtained, depending on the crystal directions and relative positions between two W defects. Further analysis indicates that a Ruderman-Kittel-Kasuya-Yosida (RKKY) like behavior plays an important role in the magnetic order when the distance between W atoms is relatively large. However, when it is rather small (<3.0 Å), the systems converge to paramagnetic states due to their direct interactions between W defects. These findings are helpful for better understanding the origin of FM order in 4d or 5d transitions metal doped graphene.