Difference in AC magnetization between suspended and immobilized magnetic nanoparticles in Néel-relaxation dominant case: Effect of easy axis alignment in suspended nanoparticles

Keiji Enpuku, Ahmed L. Elrefai, Jinnya Gotou, Shuya Yamamura, Teruyoshi Sasayama, Takashi Yoshida

Research output: Contribution to journalArticlepeer-review

Abstract

Magnetic nanoparticles (MNPs) have been widely studied for bio-sensing applications, where suspended and immobilized MNPs can be magnetically distinguished using their different magnetic properties. We study magnetic properties of suspended and immobilized MNPs when the Néel relaxation time is much shorter than the Brownian. We show in both numerical simulation and experiment that they have different magnetic properties such as AC magnetization curves and harmonic spectra even though the dynamic behavior of both MNP types is primarily dominated by Néel relaxation. This difference is caused by the partial alignment of the easy axes in suspended MNPs when an AC magnetic field is applied. We introduce a distribution function for the angle of easy axis alignment. We also show a method to evaluate the distribution function from the measured AC magnetization curve and clarify the relationship between easy axis alignment and the AC field strength. Using the distribution function, we can quantitatively discuss the effect of easy axis alignment on the magnetic properties of suspended MNPs. The obtained results provide a basis for using MNPs in bio-sensing.

Original languageEnglish
Article number113903
JournalJournal of Applied Physics
Volume130
Issue number11
DOIs
Publication statusPublished - Sep 21 2021

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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