Self-assembled epitaxial and polycrystalline magnetic nickel nanocrystallites

Kumar, D.; Zhou, H.; Nath, T. K.; Kvit, Alex V.; Narayan, J.
October 2001
Applied Physics Letters;10/22/2001, Vol. 79 Issue 17, p2817
Academic Journal
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 Al[sub 2]O[sub 3] 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 Al[sub 2]O[sub 3] 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 (∼190 K) is significantly higher than that of Ni–Al[sub 2]O[sub 3] sample (∼30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (H[sub 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[sub B] and H[sub c] of Ni–TiN samples with respect to T[sub B] of Ni–Al[sub 2]O[sub 3] samples are believed to be associated with preferred alignment of nanocrystallites. © 2001 American Institute of Physics.


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