Low temperature hydrogen treatment of Fe doped ZnO ferromagnetic semiconductor

Ferromagnetism of Zn_1-xFe_xO (x=0.00, 0.01, 0.03, 0.05, 0.07, 0.10) powder at room temperature, fabricated by sol-gel method, is investigated. The dried powder is grounded and annealed at 650°C for 6 h in H₂ 5%/Ar bal. gas atmosphere. Hydrogen treatment is employed to control phase separation. X-ray diffraction with CuKα radiation of the samples reveal that the doping of iron does not change the wurzite structure of ZnO for doping concentrations below x = 0.07. Above x = 0.10, some secondary peaks appeared, which are defined as phase separation of FeO. Rietveld refinement shows that Zn_0.99Fe_0.01O has a hexagonal crystal structure at room temperature. Measured magnetic hysteresis loops determine a ferromagnetic behaviour of the samples with coercivity of 200∼220 Oe. Also, it is noteworthy that the magnetic moment per Fe atom increases until x=0.07 but decreases in the x=0.10. This phenomena can be explained by decrease of Fe ions which contribute to Zn(Fe)O, and it is closely related to the low antiferromagnetic Neel temperature for the second phase of FeO (∼210 K).