Defects versus doping for percolation of magnetism

Magnetism's tangible origin in magnetic oxide semiconductors has yet to be discovered. According to the extensive literature review, magnetism percolation in semiconducting oxides is not limited to a single compound or preparation technique, but rather is diverse to various undoped and doped materials. Based on the reports of the previous decade, here, this chapter emphasizes the four major contributions to the magnetism in: (1) undoped oxide semiconductors; (2) defects induced magnetism; (3) transitions metal (TM)-doped oxide semiconductors; and (4) rare earth (RE)-doped oxide semiconductors. Hitherto, the origin of magnetism used to be considered as the unpaired d electrons present in the material. However, the emergence of d0 magnetism in undoped semiconductors like TiO2, ZnO, CeO2, CaO, SnO2, etc. have changed the perspective toward the understanding of the cause of magnetism. We now understand that unpaired d electrons are not the only requirement for the existence of ferromagnetism. Several developed models have demonstrated defect-induced ferromagnetism. The vacancies and defects responsible for ferromagnetism in these systems have also been determined using theoretical calculations. On the other hand, ferromagnetism is more prominent in systems doped with TM or RE ions. Furthermore, the substitution of a dopant ion for a host cation alters the electronic structure, resulting in changes in intrinsic properties such as ferromagnetism. As a result, the origin of magnetism in undoped and doped oxide semiconductors is still unknown. As a result, this chapter provides a detailed description of the percolation of magnetism caused by defects and doping in oxide semiconductors.