ZnO Magnetic Semiconductor By Mechanical Alloying

It is generally believed that the usefulness of ferromagnetic wide band gap semiconductors for spin electronics applications requires the existence of a coupling between ferromagnetic and semi conducting properties. As a result, dilute magnetic semiconductors (DMS) produced by doping transition metal ions into nonmagnetic semiconductors had drawn much attention. There have been numerous recent reviews on DMS, which lead to many new interesting properties. There are many techniques for obtaining samples, but the magnetic properties were in diverse results. In some cases, even the conclusion of intrinsic ferromagnetism remained controversial. So far the system of Fe-doped ZnO has seldom been investigated, so we carried out experiments on the system of Fe-doped ZnO and (Fe, Cu) co-doped ZnO by mechanical alloying. X-ray diffractrometer (XRD), Vibrating Sample Magnetometer (VSM), Mossbauer spectra were taken to investigate the structural and magnetic properties of the samples.Zn_1-xFe_xO (x = 0.0306, 0.0509, 0.0708, 0.0989) compounds were fabricated by mechanical alloying. The X-ray diffraction patterns showed that zinc oxide (ZnO) of single phase with wurzite structure were obtained below x=0.0708. The samples were examined for the magnetic property using VSM, indicating ferromagnetic behavior with the Curie temperature higher than room temperature, and the magnetism decreased as the content of iron increased. The ⁵⁷Fe Mossbauer spectra was conducted to further determine the magnetic behavior, and revealed that Fe atoms dissolve in the ZnO lattice in Fe²⁺ and Fe³⁺ state. Some of the iron did not dissolve in the ZnO lattice while the iron content x>0.0708. The insoluble iron appeared as a sextet in the Mossbauer spectra and resulted in the increasing magnetic property.Zn_0.93-xFe_0.07Cu_xO (x = 0.0, 0.005, 0.01, 0.015, 0.020) compounds were fabricated by mechanical alloying. Applying appropriate conditions, doping Fe alone can induce ferromagnetism in ZnO itself, while co-doping Cu might enhance the magnetic moment for some extent below x=0.01. The X-ray diffraction patterns showed that zinc oxide (ZnO) of single phase with wurzite structure were obtained below x=0.01. The samples were examined for the magnetic property using Vibrating Sample Magnetometer (VSM), indicating ferromagnetic behavior with the Curie temperature higher than room temperature. Besides, ⁵⁷Fe Mossbauer spectrum was conducted to determine the magnetic behavior, and revealed that Fe atoms dissolve in the ZnO lattice in Fe²⁺ and Fe³⁺ state. In the case of Zn_0.91Fe_0.07Cu_0.02O, the majority of the Fe ions in the system go into ZnFe₂O₄ instead of dissolve in the ZnO lattice. The magnetic property of the sample was paramagnetic.