Diluted magnetic characteristics of Ni-doped AlN films via ion implantation

Abstract

The structural and magnetic properties, as well as the mechanism of magnetization, of Ni-implanted AlN films were studied. AlN was deposited on Al2O3 substrates by metalorganic chemical vapor deposition (MOCVD), and subsequently Ni ions were implanted into the AlN films by Metal Vapor Arc (MEVVA) sources at an energy of 100 keV for 3 h. The films were annealed at 900°C for 1 h in the furnace in order to transfer the Ni ions from interstitial sites to substitutional sites in AlN, thus activating the Ni3+ ions. Characterizations were performed in situ using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and vibrating sample magnetometry (VSM), which showed that the films have a wurtzite structure without the formation of a secondary phase after implanting and annealing. Ni ions were successfully implanted into substitutional sites of AlN films, and the chemical bonding states are Ni-N. The apparent hysteresis loops prove that the films exhibited magnetism at 300 K. The room temperature (RT) saturation magnetization moment (M s ) and coercivity (H c ) values were about 0.36 emu/g and 35.29 Oe, respectively. From the first-principles calculation, a total magnetic moment of 2.99 μB per supercell is expected, and the local magnetic moment of a NiN4 tetrahedron, 2.45 μB, makes the primary contribution. The doped Ni atom hybridizes with four nearby N atoms in a NiN4 tetrahedron; then the electrons of the N atoms are spin-polarized and couple with the electrons of the Ni atom with strong magnetization, which results in magnetism. Therefore, the p-d exchange mechanism between Ni-3d and N-2p can be the origin of the magnetism. It is expected that these room temperature, ferromagnetic, Ni-doped AlN films will have many potential applications as diluted magnetic semiconductors.