An effective way to increase the high-frequency permeability of FeO nanorods

Uniform Fe 3 O 4 magnetic nanorods (NRs) were successfully synthesized and oriented in epoxy resin under a rotating magnetic field. Magnetic induction fields within and around a single Fe 3 O 4 nanorod in the remanence state were obtained by off-axis electron holography. The induction fields indicated a single domain state of the highly anisotropic Fe 3 O 4 nanorod due to its strong magnetic shape anisotropy. Quantitative magnetic moment analysis of the obtained phase image yielded an average magnetization of 0.53 T of a single Fe 3 O 4 nanorod. Moreover, the real part of the permeability ( μ ′) of magnetic-oriented Fe 3 O 4 NRs is obviously higher than that of random Fe 3 O 4 NRs in the GHz range. The oriented Fe 3 O 4 NRs exhibit a higher resonance peak at 4.75 GHz compared to the bulk counterpart (1.2 GHz) in the frequency dependence of μ in the range of 1-10 GHz. Moreover, the calculated μ value of the oriented Fe 3 O 4 NRs could be improved to 4.22 with the increased dipolar interaction strength using the OOMMF software. These results could play a guiding significance in the development of an effective method to improve the permeability of magnetic nanomaterials at GHz working frequency. The oriented Fe 3 O 4 magnetic nanorods (NRs) were successfully synthesized with a high-frequecy permeability.