Material Characterization Study of Magnetite Nanocrystals for RF Sensing

Magnetite nanocrystals show promise for electrically small gigahertz frequency applications, which could lead to miniaturizing transformer cores and new sensing technologies. This work presents a rigorous radiofrequency characterization of these nanocrystals using vector network analyzer (VNA) ferromagnetic resonance (FMR) measurements. For the first time, two different average diameters of Fe₃O₄ nanocrystals are investigated (7.3 and 20.2 nm). When the VNA-FMR results were compared to micromagnetic simulations, the magnetic anisotropy (K₁) deviated from the ideal mean orientation value of K₁/2 to K₁/80 for the 7.3 nm nanocrystal. In contrast, the obtained magnetic anisotropy in 20.2 nm nanocrystals slightly deviated to K₁/11 due to less structural deformations. These findings resulted in a newly proposed methodology for an approximate simulation based on VNA-FMR measurements. In addition, this work estimates the approximate amount of nanocrystals needed to measure a useful VNA-FMR spectrum.