Magnetic properties of polydisperse and monodisperse NiZn ferrite nanoparticles interpreted in a surface structure model

Static and dynamic magnetic properties of cuboctahedrally truncated polydisperse, rf plasma torch synthesized NiZn ferrite nanoparticles have been studied. The transmission electron microscopy (TEM) determined nanoparticle size distribution was log-normal (mean=11.7nm, σ=10.9nm). Magnetic properties are interpreted using a polyhedral surface structure model, for the observed (111) and (100) nanoparticle surfaces. To determine the magnetic anisotropy fields and isolate anisotropy contributions of the (100) and (111) surfaces, rf transverse susceptibility (TS) measurements were performed. The TS data showed broad peaks observed at characteristic anisotropy fields, consistent with the large particle size distribution. A surfactant-mediated size selection technique was used to obtain monodisperse nanoparticles with a log-normal size distribution (mean=6nm, σ=2.9nm). TS measurements on the monodisperse samples showed absence of anisotropy peaks, with the smaller particles being dominated by (111) surfaces with isotropic canted triangular spin structures.