Room Temperature Ferromagnetism in Nickel Doped Cerium Oxide Nanoparticles
Type of Culminating Activity
Master of Science in Materials Science and Engineering
Materials Science and Engineering
Powders comprised of nanocrystalline Ce1-xNixO2 were obtained using the sol-gel synthesis route. Precipitated gels were dried at 50°C for 12 hours before being ground in an agate mortar and annealed at 450°C for 3 hours. X-ray diffraction confirmed cubic CeO2 with lattice parameter a near the expected 5.41 Ǻ for all x with particle size decreasing from 9 nm for x = 0 as to 4 nm for x = 0.1o. Transmission electron microscopy verified these particle sizes. Lattice strain from x-ray diffraction data showed a minimum for x = 0.04. Optical reflectance showed a direct band gap varying with x from 3.8 eV for x = 0 decreasing to 3.3 eV for x = 0.04, then increasing again, following the same trend as the lattice strain. Room temperature magnetic measurements showed ferromagnetic hysteresis for Cel-xNixO2 for 0 < x ≤ 0.10, with a maximum magnetization of 8.6 x 10-4 μB/Ni ion for x = 0.04. The decreased magnetization with increased Ni concentration is expected as the higher concentration results in antiferromagnetic coupling between neighboring Ni ions. Electron paramagnetic resonance confirmed presence of Ni2+ incorporated insterstitially and substitutionally into CeO2, with the interstitial component increasing with x. Additional processing to enhance the room temperature magnetization was found to increase magnetization by up to 600 times for x = 0.10. This magnetic activation process was found to be accompanied by the loss of the interstitial Ni2+ signal in electron paramagnetic resonance studies.
Thurber, Aaron Paul, "Room Temperature Ferromagnetism in Nickel Doped Cerium Oxide Nanoparticles" (2008). Boise State University Theses and Dissertations. 538.