The room-temperature ferromagnetism of defect-rich ZnMgO semiconductor thin films

The magnetic properties of Mg-doped ZnO thin films grown under different oxygen pressures PO and annealing temperatures Ta on Si (001) substrates by pulsed-laser deposited (PLD) were investigated. The hysteresis curve at room temperature (RT), measured with a high-resolution magnetometer (∼10−6 emu), revealed the presence of a ferromagnetic state for all Mg-doped ZnO thin films that were investigated. Interestingly, a significant magnetic signal was observed for an amorphous Zn0.35Mg0.65O thin film; RT ferromagnetism in amorphous ZnMgO films has rarely been reported. Photoluminescence (PL) spectroscopy measurements, as well as microstructure analysis, suggest that RT ferromagnetism in ZnMgO thin film, when exposed to an oxygen atmosphere or annealed in air, is related to oxygen interstitials, Oi, and zinc vacancies, VZn. Strong polarization from electrons trapped on these defects and vacancies induces the magnetic properties. We reveal a possible approach for explaining the origin of magnetism by a defect-induced mechanism rather than the conventional carrier-induced mechanism. In our proposed mechanism, a defect-rich polarizing effect may play a crucial role in the magnetic behavior of ZnO-based semiconductors.