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Size- and Composition-Dependent Radio Frequency Magnetic Permeability of Iron Oxide Nanocrystals

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journal contribution
posted on 23.12.2014 by Hongseok Yun, Xiyu Liu, Taejong Paik, Duraivelan Palanisamy, Jungkwun Kim, William D. Vogel, Arthur J. Viescas, Jun Chen, Georgia C. Papaefthymiou, James M. Kikkawa, Mark G. Allen, Christopher B. Murray
We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals. All nanocrystalline samples are confirmed to be in the superparamagnetic state at room temperature by SQUID magnetometry. Through the one-turn inductor method, the ac magnetic properties of the nanocrystalline oxides are characterized. In magnetite-rich iron oxide nanocrystals, size-dependent magnetic permeability is not observed, while maghemite iron oxide nanocrystals show clear size dependence. The inductance, resistance, and quality factor of hand-wound inductors with a superparamagnetic composite core are measured. The superparamagnetic nanocrystals are successfully embedded into hand-wound inductors to function as inductor cores.