Ferromagnetic resonance in the complex permeability of an Fe3O4-based ferrofluid at radio and microwave frequencies

• Published in: Journal of magnetism and magnetic materials 2019-11, Vol.489, p.165387, Article 165387
• Main Authors: Dubreuil, J., Bobowski, J.S.
• Format: Article
• Language: English
• Subjects: Dependence; Ferrofluids; Ferromagnetic resonance; Ferromagnetism; Field strength; Iron oxides; Magnetic fields; Magnetic permeability; Microwave absorption; Microwave frequencies; Nanoparticles; Permeability
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2019.165387

•We have made a sensitive measurement of the complex permeability of a ferrofluid.•Our measurements have revealed a clear ferromagnetic resonance.•The measurements span a wide range of RF and microwave frequencies.•We have uncovered a small dip feature in the real part of the permeability.•We developed a new custom experimental method for these measurements. The complex permeability of an iron-oxide nanoparticle suspension has been measured as a function of magnetic field strength at radio and microwave frequencies using a loop-gap resonator. The system studied was a water-based ferrofluid containing Dextran-coated Fe3O4 particles with an average diameter of 8 nm. The real part of the permeability increased sharply beyond a frequency-dependent threshold value of the static magnetic field before saturating. Just beyond this threshold field, there was a peak in the imaginary part of the permeability. The permeability measurements, which exhibited features associated with ferromagnetic resonance, were used to determine the dependence of the microwave absorption on static magnetic field strength. Using the absorption data, the g-factor of the ferrofluid was found to be 1.86 ± 0.07.