Magnetic Properties and Structure of Iron-Nickel Nanoparticles and Thin Films Synthesized by Pulsed Laser Deposition.

摘要

The study of new combinations of self-assembled magnetic materials in nanoparticle and thin film form is becoming increasingly important with the continuous shrinking of data storage device size with higher densities. The work presented in this dissertation is focused towards synthesis, structural characterizations, and magnetic properties of an L10 iron-nickel (Fe50Ni50) phase that has a potential to replace noble metals based L10 magnetic materials, such as Ni-Pt, Fe-Pt, being used as recording media. Fe50Ni50 was fabricated using a pulsed laser disposition (PLD) method under various deposition conditions, the most important among which was the substrate temperature. The substrate temperature was varied all the way from liquid nitrogen boiling temperature of 77K (-196 ºC) to high temperatures up to 600 ºC. In order to understand and optimize the formation of L10 phase, the PLD method was used to fabricate FeNi in three distinct ways: (i) FeNi films were prepared using a FeNi composite (alloy) target, (ii) FeNi films were fabricated in a multilayered structure using sequential ablation of Fe and Ni targets, and (iii) FeNi thin films were fabricated in alumina (Al2O3)/FeNi/Al2O 3 sandwich structures.;To promote the stabilization of L10 FeNi phase, a thin film layer of gold catalyst was deposited prior to the deposition of FeNi films. FeNi films deposited in the presence or absence of gold catalyst were annealed at 600°C for 1 hour to study effect of annealing that has been found to bring about significant alterations in structural and magnetic properties. The substrate materials such as silicon and sapphire were also found to play a significant role in the microstructural and magnetic properties of the FeNi films. The FeNi samples deposited at liquid nitrogen temperature were found to be completely glassy (amorphous), and they exhibited a perfect superparamagnetic behavior, making them good candidates for magnetic biomedical devices.