Date of Award
Master of Applied Science (MASc)
Materials Science and Engineering
Ni-Fe alloys have been used in industrial applications over the past century due to their unique mechanical and magnetic properties. Currently, researchers are interested in enhancing the performance of Ni-Fe alloys by modifying their microstructure. An example of this would be the use of ultra-fine nanocrystalline Ni-Fe alloys for magnetic shielding products that are uniquely shaped and cost effective. These nanocrystalline materials usually exhibit good soft magnetic properties, such as high saturation magnetization, low coercivity and good magnetic permeability. The following study has been devoted to the magnetic properties of electrodeposited nanocrystalline Ni-Fe alloys.
The structure and texture of electrodeposited Ni-Fe alloys was studied by two-dimensional XRD. The Ni-Fe alloys with Fe content from 24.9at. % to 54.2at. % were comprised exclusively of the FCC phase. For 60.2at. % Fe sample, a mixed phase of BCC and FCC structure was found. The lattice parameter increased with increasing Fe content until 54.2at. %, and then decreased due to the presence of BCC structure. The increase in lattice parameter was attributed to the iron replacement of nickel in the Ni crystalline lattice. Texture analysis shows that all Ni-Fe alloys with different Fe content exhibit the fiber texture with a major component of theaxis aligned perpendicular to the sample plane. A second component iswith a significantly lower volume fraction. It also shows that the Ni-Fe alloy with 44.2at. % Fe exhibits the highest volume fraction of random orientation.
Magnetic measurements showed that all Ni-Fe nanocrystalline alloys exhibit soft magnetic properties with narrow hysteresis loops. The saturation magnetization increased linearly with increasing Fe content. The magnetization at T = 2K were slightly higher than that at T = 298K. The lowest coercivity~6Oe was obtained at 44.2 at. % Fe content.
Good agreement between Random Anisotropy Model (RAM) theory and experimental data for all the Ni-Fe alloys has been obtained. By fitting the high field magnetization curve with the Law of Approach to Saturation (LATS), the magnetocrystalline anisotropy constant (Keff) were obtained. Keff decreased with increasing temperature. Also, the ferromagnetic exchange lengths for each Ni-Fe alloy were calculated. They are 26nm, 21nm, 19nm, 18nm, 17nm for Ni-24.9at.%Fe, Ni-33.1at.%Fe, Ni-44.2at.%Fe, Ni-54.2at.%Fe, Ni-60.2at.%Fe at room temperature, respectively. The exchange lengths are larger than the average grain size (D) for all of the samples. The results confirmed the feasibility of Random Anisotropy Model for the prediction of the magnetic properties of the nanocrystalline Ni-Fe alloys fabricated by electrodeposition.
Wang, Minghe, "Magnetic Properties of Electrodeposited Nanocrystalline Ni-Fe alloys" (2012). Open Access Dissertations and Theses. Paper 7575.
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