Jem 4010

The particle size and morphology of silica-coated magnetic nanoparticles were determined by transmission electronic microscopy (TEM) using a JEM-4010 (JEOL; Tokyo, Japan) at an accelerating voltage of 400 kV. The magnetic nanoparticles and silica-coated magnetic nanoparticles were characterized by powder X-ray diffraction (XRD), using a Rigaku D/MAX-2500 diffractometer (Rigaku; Tokyo Japan) using filtered Cu Kα radiation, and the data were collected for 2θ of 20.0° to 80.0°. The magnetization of silica-coated magnetic nanoparticles at room temperature up to 10 kOe was measured by vibrating sample magnetometer (VSM) using a VSM 4179 (Oxford Instruments; Oxfordshire, UK). Fourier transform infrared (FT-IR) spectroscopy was used to identify the functionalized MNPs@SiO₂. The FT-IR spectra were recorded on a V-460 (JASCO; Easton, MD, USA) FT-IR spectrometer using KBr pellets. Spectra were obtained at a resolution of 4 cm^-1, and the wavenumber range from 4,000 to 650 cm^-1. The fluorescence intensity and absorbance of the samples were measured using microplate reader Infinite M200 (Tecan Ltd). The fluorescence was measured five times for each sample with a 20-μs integration time.

The morphological characteristics and structures of the samples were studied using a scanning electron microscope (SEM, JEOL JSM-6700F) equipped with an energy-dispersive X-ray spectroscopy (EDX) and a high-resolution transmission electron microscope (HRTEM, JEOL JEM-4010). The XRD measurements were carried out with a Rigaku X-ray diffractometer with Cu Kα radiation (λ = 1.5418 Å) at a scan rate of 2º/min at an operating voltage of 40 keV and 20 mA. X-ray photoelectron spectroscopy (XPS, K-alpha, Thermo VG, U.K.) employing a monochromated Al X-ray source (Al Kα line: 1486.6 eV) was used to obtain the binding energy plots of the samples.

X-ray diffraction analysis of the bulk composite samples was analyzed using Rigaku D/MAX-2500/PC with Cu Kα radiation. The microstructure of the composites was examined by using a high-resolution transmission electron microscope (HRTEM, JEM- 4010, JEOL) and scanning electron microscopy (SEM, Verios 460 L, FEI). Rectangular sample (2 × 2 × 9 mm³) were cut for the estimation of electrical conductivity and Seebeck coefficient, which were measured by using a four-point probe (TPMS, ZEM-3). High temperature charge transport performance were measured up to 730 K by using a high-temperature Hall measurement (HT-Hall, Toyo Corporation, ResiTest 8400). A circular disc specimen of 1 mm in thickness and 10 mm in diameter was used for thermal diffusivity measurement using a laser flash method (DLF-1300, TA instrument). The density was measured by Archimedes-principle. Thermal conductivity (κ) was calculated from the relation, diffusivity (α) × density (ρ) × specific heat capacity (C_p).