Morphology and Magneto-optical Properties of Amorphous AlN Films Doped with Nickel
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Morphology and Magneto-optical Properties of Amorphous AlN Films Doped with Nickel W. M. Jadwisienczak1, H. Tanaka1, G. Chen2, M. Kordesch2, A. Khan3 1
School of EECS, Ohio University, Athens, Ohio, U.S.A. Department of Physics and Astronomy, Ohio University, Athens, OH, U.S.A. 3 Department of Chemistry and Biochemistry, Ohio University, Athens, OH, U.S.A. 2
ABSTRACT Structural and magneto-optical properties of Ni-doped amorphous AlN layers (a-AlN) deposited by radio frequency (rf) sputtering on Silicon (001) substrates were investigated. The as-grown material exhibits weak ferromagnetic behavior as evidenced by the magneto-optic Kerr effect (MOKE) measurement with Kerr rotation less than 100 µrad at room temperature regardless of the Ni fraction. The samples with a Ni concentration below 10 at.% show a weak but monotonically increasing MOKE signal with post-growth annealing temperature. A hundred-fold increase in the Kerr rotation value was observed for samples with Ni content exceeding 20 at.% after thermal annealing at 450°C in nitrogen; and the Kerr rotation value abruptly decreases above that temperature. The morphology of as-grown and annealed a-AlN:Ni films were characterized by small angle x-ray scattering and transmission electron microscopy. It was found that the as-deposited film contains nano-particles of different sizes with average diameters less than 30 nm. The size distribution of nano-particles in the thermally annealed a-AlN:Ni was studied as a function of annealing time and temperature. The results correlate well with those obtained from the MOKE measurements. INTRODUCTION Magnetically ordered amorphous materials and magnets exhibit a wide range of technologically important materials that rely on magnetic ordering and the dynamic interactions between spin excitations and electronic transport phenomena [1,2]. Amorphous III-nitride semiconductors doped with Transition Metals (TM) and rare earth ions are suitable for prospective applications in spintronics because of a strong magnetic moment associated with the metallic impurities [3,4] and the possibility of easy modification of the magnetic domain environment. The unique feature of a-AlN:TM, in general, is that a long-range magnetic ordering is possible, while the long-range order does not exist in the distribution of constituent atoms. This implies that magnetic and nonmagnetic atoms in an a-AlN:TM lose completely the periodicity of lattice in its crystalline counterpart and form a non-crystalline solid. The high doping of magnetic transition metals is extremely difficult with the commonly used doping technique such as thermal diffusion because the solubility of the magnetic impurities is too low, especially in III-V materials [5]. Furthermore, doping with TM at high concentrations is prone to morphological inhomogeneity like nano-size precipitates and atom clustering. Experimental techniques like small angle x-ray scattering (SAXS) and high resolution transmission electron microscopy (HRTEM) allow for detailed investigations of nano-size partic
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