Impurity-related defect complexes-mediated ferromagnetism and impurity band hopping conduction in a highly compensated Zn-doped SnO₂

We reported the ferromagnetism (FM) and electrical transport properties induced by donor-acceptor compensated defect complexes and related impurity bands in highly compensated Zn-doped SnO2 thin films. Various characterizations were used to study the optical, electrical, luminescent, and magnetic properties of SnO2 films with Zn dopants. Comparing with the paramagnetic nature of undoped n-type SnO2, we observed a room tem-perature d(0) FM in the highly compensated and p-type Zn-doped SnO2 films with a low conductivity of similar to 10(-3) Scm(-1), suggesting a strong correlation between ferromagnetism and the donor-acceptor compensation. The coercive field, remanent and saturation magnetization for the Zn-doped SnO2 film at 300 K are 310 Oe, 0.8 emu/cm(3), and 2.6 emu/cm(3), respectively. A detailed analysis for temperature-dependent resistivity indicates that the electrical conduction behavior of Zn-doped SnO2 at low temperatures follows the variable range hopping mechanism proposed by Mott and confirms that impurity bands occur at the Fermi level. As the concentration of Zn dopants increases, the fitting Mott temperature gradually rises, suggesting the contribution of Zn impurities to form the impurity bands where the carriers are localized. First-principles calculations reveal that the Zn substituting Sn site (Zn-Sn) defect with a low formation energy is responsible for the transformation of the charge carrier type. Furthermore, the oxygen vacancy (V-O) between two nearest-neighbor ZnSn defects can stabilize the ferromagnetic coupling and form Mott's variable range hopping conduction derived from the localized carriers in the compensated impurity bands. Our results are of significance for the better understanding of the physical mechanisms underlying the effects of impurity/defect bands on the magnetic and electrical properties of the SnO2 with Zn dopants.