Improved magnetic properties of self-assembled epitaxial nickel nanocrystallites in thin-film ceramic matrix
- PDF / 339,087 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 0 Downloads / 165 Views
V. Craciun and Rajiv K. Singh Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (Received 13 June 2001; accepted 13 December 2001)
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 (Hc) 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 TB and Hc of Ni–TiN samples with respect to TB of Ni–Al2O3 samples are believed to be associated with preferred alignment of nanocrystallites.
I. INTRODUCTION
There is a wide recognition of critical length scales in the nanometer range that define the material structure and organization which ultimately determine the fundamental macroscopic properties of solid-state materials. An important class of materials, where the critical length scales in nanometer range play a dramatic role, is nanomagnetic materials.1– 4 When the size of magnetic particles is reduced to a few tens of nanometers, they exhibit a number of outstanding physical properties such as giant magnetoresistance, superparamagnetism, large coercivities, high Curie temperature, and low saturation magnetization as compared to the corresponding bulk values. Due to realization of these outstanding physical properties with size reduction, magnetic nanoparticles are bringing revolutionary changes in a variety of applications.5 The textured nanoparticles are expected to have even higher
a)
Also at North Carolina A T State University, Greensboro, NC 27411.
738
http://journals.cambridge.org
J. Mater. Res., Vol. 17, No. 4, Apr 2002 Downloaded: 20 Mar 2015
anisotropy energy (K) and lower saturation magnetization yielding systems with still higher coercivity (⳱2K/ Ms). This expectation is what precisely constitutes the basis of the present investigation. We are reporting here the fabrication and magnetic properties of self-
Data Loading...
