Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

Defect-induced ferromagnetism has triggered a lot of investigations and controversies. The major issue is that the induced ferromagnetic signal is so weak that it can be sufficiently accounted for by trace contamination. To resolve this issue, we studied the variation of the magnetic properties of SiC after neutron irradiation with fluence covering four orders of magnitude. A large paramagnetic component has been induced and scales up with defect concentration, which can be well accounted for by uncoupled divacancies. However, the ferromagnetic contribution is still weak and only appears in the low fluence range of neutrons or after annealing treatments. First-principles calculations hint towards a mutually exclusive role of the concentration of defects: A higher defect concentration favors a larger magnetic interaction at the expense of spin polarization. Combining both experimental and first-principles calculation results, the defect-induced ferromagnetism can probably be understood as a local effect which cannot be scaled up with the volume.