Possible defect-induced ferromagnetism in Cr doped SiC single crystals

Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.