Improved magnetic properties of self-assembled epitaxial nickel nanocrystallites in thin-film ceramic matrix

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 was investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in the case of the 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 the 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 the Ni-TiN sample (approximately 190 K) is significantly higher than that of Ni-Al2O3 sample (approximately 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 in amorphous alumina matrix. 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.