Ferromagnetic Resonance of All Oxide Core / Shell Nanoparticle Variants

Core-shell magnetic nanoparticles (MNPs) are being considered for various applications in spintronics as well as in the bio-medical field. Ferromagnetic Resonance (FMR) is a widely-used technique for determining magnetic properties such as bulk magnetization and anisotropy, gyromagnetic ratio / g-factor, and damping. Broadband FMR using a co-planar waveguide (CPW) is well-suited for examining properties of thin film samples, but MNPs present some challenges. MNPs can have a wide distribution of sizes and crystalline orientation. Also, at room temperature MNPs are generally superparamagnetic, where the magnetic orientation is unstable against thermal fluctuations. This research sought to adapt the standard CPW-FMR methods for thin films to characterize the resonant responses of MNPs, starting with commercially available magnetite (Fe₃O₄) MNPs and progressing to more complex Fe₃O₄/CoFe₂O₄ core-shell nanoparticle variants. Protocols were developed for mounting the different MNPs onto substrates suitable for CPW-FMR. The temperature- and frequency-dependent resonant response of the MNPs was explored. The determination of specific sample properties extracted from the CPW-FMR methods will be discussed.