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

• Published in: ACS nano Vol. 8; no. 12; pp. 12323 - 12337
• Main Authors: Yun, Hongseok, Liu, Xiyu, Paik, Taejong, Palanisamy, Duraivelan, Kim, Jungkwun, Vogel, William D, Viescas, Arthur J, Chen, Jun, Papaefthymiou, Georgia C, Kikkawa, James M, Allen, Mark G, Murray, Christopher B
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 23.12.2014
• Subjects: Inductors; Iron oxides; Magnetic permeability; Mossbauer spectroscopy; Nanocrystals; Nanostructure; Oxides; Radio frequencies; magnetite; radio frequency; magnetic susceptibility; maghemite; inductor; superparamagnetism
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/nn504711g

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.