Self-assembled epitaxial and polycrystalline magnetic nickel nanocrystallites

Nanocrystalline nickel particles were embedded in amorphous alumina and crystalline TiN matrices using a pulsed-laser deposition process to investigate the effect of texturing on magnetic properties of nickel nanocrystallites. The crystalline quality of both the matrix and magnetic particles were investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in case of TiN matrix and polycrystalline in Al2O3 amorphous matrix. The Ni nanocrystals on TiN/Si grow epitaxially because the TiN acting as a template grows epitaxially on Si substrate via domain epitaxy. On the other hand, Ni nanocrystals in Al2O3 matrix are polycrystalline because of the amorphous nature of the alumina matrix. Magnetization versus temperature measurements have shown that the blocking temperature, above which the samples lose magnetization-field (M-H) hysteretic behavior, of Ni-TiN sample (similar to 190 K) is significantly higher than that of Ni-Al2O3 sample (similar to 30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (H-c) of the two samples, measured from M-H data, indicates that epitaxial Ni nanocrystals also exhibit significantly higher coercivity than polycrystalline Ni particles. The high values of T-B and H-c of Ni-TiN samples with respect to T-B of Ni-Al2O3 samples are believed to be associated with preferred alignment of nanocrystallites. (C) 2001 American Institute of Physics.