Room Temperature Ferromagnetism Effects of Transition Metal (M=Ni or Co) Co-doping with Y in Ce1-x-yMxYyO2 Nanoparticles
Dr. Charles Hanna
The utility of nanoparticles has, as a result of extensive research, grown drastically over the last few years. In the past, ceria (cerium oxide, CeO2) has been used in many different industries and has a wide range of applications from use in catalytic converters in automobiles to more modern uses in fuel cells or in hydrolysis for hydrogen production, but only recently has it been shown to exhibit useful magnetic properties as a nanoparticle. Further work is being done to study the viability of CeO2 as a pragmatic spintronics material, where both the charge and spin of electrons are utilized to further miniaturization and multi-functionality of materials. Research by several groups has previously indicated that ceria exhibits room temperature ferromagnetism (RTFM), a requirement for practical and useful devices. RTFM has been proposed to be due to oxygen vacancies, transition metal dopants (such as Ni and Co), and/or surface defects. It is our goal in this experiment to examine how doping ceria nanoparticles affects the RTFM. Recent reports have indicated that adding yttrium to the transition metal doped CeO2 system can increase the ferromagnetic moment of thin film samples. Therefore, we attempted to enhance the ferromagnetic properties of ceria nanoparticles through co-doping with Ni or Co and Y. / CeO2 nanoparticles were synthesized by co-dissolution of cerium acetate and a transition metal acetate precursor in denatured ethanol with lithium hydroxide. The solution was brought to a temperature of 70° C for 90 min. After heating, the solution was cooled to room temperature before adding n-heptane. Once the n-heptane was added, it was aged for 1-2 days to allow for particle growth. After aging, the solution was centrifuged at approximately 41,000g and washed with a water-ethanol-water cycle. The particles were then dried in an oven at 50° C for at least 12 hours before the powder was ground by mortar and pestle for characterization. Atomic concentrations of the transition metal (M) dopant x and the yttrium y are given by the molar ratio x = [M]/([M]+[Ce]) and y = [Y]/([Y]+[Ce]) respectively. All samples were produced in triplicate to obtain an average and standard deviation. / Based on the comparison between the saturation magnetization saturation (Ms) of pure ceria and the results of doping, it can be seen that doping does alter the RTFM of ceria nanoparticles. It was found that the optimal amount of yttrium was around y = 0.02 to achieve maximum Ms with good repeatability. It is also worth noting that when the x was varied without any yttrium, Ms peaked at x = 0.02, but when they were co-doped with 2% Y the peaks both shifted to give maximum magnetic moment for x = 0.03. Further work is required to understand the role of yttrium in the transition metal doped oxide system.
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