Codoping induced enhanced ferromagnetism in diluted magnetic semiconductors

The experimentally observed d (0)-magnetism and its subsequent attribution to the presence of structural and topological defects has opened the way for engineering the magnetic properties of diluted magnetic semiconductors (DMSs) and transition metal oxides (TMOs). Doping and codoping constitute the most commonly used processes (either experimentally or theoretically) for developing and studying this type of defect-induced magnetism. The focus of the present review is to highlight the basic features of the defect magnetism which have been observed over diverse systems, while emphasizing the local, holistic and synergistic response of the host materials to their doping and investigating their role in the development of the magnetic coupling (MC) that is developed among the magnetic dopants. Ab initio computational results elucidate the local aspects of the MC (charge and spin transfers between dopants and their first nearest neighboring anion ligands) and their relation with holistic processes which are reflected in the band structure, and the shifts of both the d- and p-band centers of the doped material (compared to the undoped one). In view of these results the MC between the magnetic dopants is framed within the newly proposed successive spin polarization and the defect-induced defect-mediated models. The similarities found in the magnetic characteristics between the codoped DMSs/TMOs and the magnetic multilayer systems lends further support to these models which introduce new contributions to the MC that are competitive with the existing classical ones (superexchange, double exchange, s-d & p-d couplings etc).