Cluster and Thickness Dependence of Ferromagnetism in Nickel In Situ-Doped Amorphous AlN Thin Films

• Published in: Journal of electronic materials 2013-05, Vol.42 (5), p.844-848
• Main Authors: Tanaka, H., Jadwisienczak, W. M., Kaya, S., Chen, G., Wan, C., Kordesch, M. E.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electrical engineering; Electronics and Microelectronics; Exact sciences and technology; Ferroelectrics; Instrumentation; Magnetic properties and materials; Magnetic properties of monolayers and thin films; Magnetic properties of surface, thin films and multilayers; Magnetism; Materials Science; Nanostructured materials; Nickel; Optical and Electronic Materials; Physics; Solid State Physics; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Thin films
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-013-2493-3

We report on magneto-optical investigations of Ni-doped amorphous AlN (a-AlN) thin films. The a-AlN was grown by radiofrequency (rf) sputtering on Si (0001) substrates at low temperature and doped with Ni at fixed concentrations with different a-AlN layer thicknesses. As-grown a-AlN:Ni layers were annealed up to 900°C for 5 min and 15 min time duration in nitrogen ambient at atmospheric pressure. Each sample was characterized by the magneto-optical Kerr effect (MOKE) in both polar and longitudinal geometries. Only the 65-nm-thick a-AlN:Ni layers showed linear enhancement of magnetization after thermal treatment up to 900°C, indicating the presence of a critical a-AlN:Ni layer thickness supporting the formation of magnetic domains. No measurable MOKE signal was observed in the longitudinal geometry for any tested samples with different thicknesses. This observation confirms that the easy magnetization axis in a-AlN:Ni layers is out of plane due to the strong magnetic anisotropy observed in polar MOKE geometry. The morphology of as-grown and annealed a-AlN:Ni films was characterized by atomic force microscopy (AFM), magnetic force microscopy (MFM), and scanning electron microscopy (SEM) and revealed the existence of nanoclusters. The size distribution of nanoclusters was studied as a function of annealing time and temperature, and the results correlate well with those obtained from the MOKE measurements.