Preparation of nano-structure soft magnetic core using Fe@SiO2 nano-particles

Fe@SiO2 nanoparticles with average size of 30 nm have been prepared and their magnetic properties have been investigated. The SiO2 coating layer has been formed by hydrolysis and polycondensation of tetraethoxysilane(TEOS). The existence of Fe and Si atoms were characterized by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) and the core-shell structure was determined by high resolution transmission electron microscopy (HRTEM). Fe nano-particles are stabilized by SiO2 thin layer with about 2 am thickness. Magnetic measurements done by a superconducting quantum interference device (SQUID) magnetometer show the Fe@SiO2 nano-particles are in ferromagnetic state. Thermal treatment has been done to increase crystalinity of the particles. With the particles, toroidal cores were made using a hydraulic press. The core has a dimension with outer-diameter of 10mm, inner-diameter of 5mm and height of 5mm. The apparent density of the core is measured as about 50% determined by Archimedes-method. The permeability of the core was measured by B-H meter within frequency of 1 MHz.