Structural and magnetic properties of ZnO nanocrystals in (Zn, Al)O films using pulse laser deposition

In this manuscript, we reported that the room temperature ferromagnetism was observed in (Zn _0.70, Al _0.30)O film, which was fabricated by a novel pheyical method (pulse laser deposition (PLD)). The film was deposited from (Zn _0.80, Al _0.20 O ceramic target onto quartz (110) substrate by PLD at 400 °C under an oxygen partial pressure of 10 ^-4 torr. TEM result shows ZnO NCs with diameter of 4-5 nm and they are quite uniformly embedded into amorphous ZnO-Al ₂O ₃ phase. The SAED shows clearly that ZnO NCs possess polycrystalline structure. The SQUID measurement shows that the film has room temperature ferromagnetism (saturation magnetization = 3.6 emu/cm ³) with Curie temperature above 300 K. The magnitude of magnetic moment of the films can be changed by tuning ZnO NCs size. Both oxygen partial pressure and film thickness studies show that the origin of ferromagnetism is possibly related to the oxygen defects at the surface of ZnO NCs.