Ferromagnetic resonance and magnetic anisotropy in biocompatible Y3Fe5O12@Na0.5K0.5NbO3 core-shell nanofibers

Y3Fe5O12@Na0.5K0.5NbO3 (YIG@NKN) core-shell nanofibers were synthesized by the coaxial electrospinning technique. For comparison, samples of YIG and NKN nanofibers were prepared. Scanning Electron Microscopy (SEM) and 3D laser-scanning confocal microscopy (TDLM) of YIG@NKN nanofibers revealed long uniform size distributed fibers with the average diameter of 100–150 nm. X-Ray diffraction (XRD) examination shows the existence of the distinct peaks of orthorhombic NKN and cubic YIG. Magnetic force microscopy (MFM) of individual YIG@NKN nanofiber demonstrates a magnetic core that is extended in one half of the diameter of the fiber. These nanofibers show obvious Ferromagnetic resonance (FMR) with resonance near 2 KOe similar to YIG fibers but in such a way that it starts to increase linearly with applying magnetic field from zero up to near resonance field. Also they show a soft magnetic behavior with saturation magnetization of 10 emu/gr. Furthermore, we propose a model to explain line shape of randomly oriented fibers and extract all the magnetic anisotropy parameters from FMR data. The results rely the shape anisotropy as dominant effect, however the dipolar field among fibers should be considered. The highest degree of asymmetry observed in the case of core-shell fibers in hard direction that it can be originated from magneto electric effects. By taking into account the observed FMR, the ability of adequate control of microwave absorption by applying magnetic field and biocompatibility, the synthesized core-shell nanofibers are the most promising candidate for clinical application such as microwave cancer thermotherapy and adjustable microwave absorbers.