Telah dilakukan perhitungan nilai ketidakpastian pengukuran pada karakteristik material magnet permanen menggunakan alat ukur Permagraph Magnet Physik Germany. Karakteristik magnet yang diukur adalah induksi remanen, Br (kG), gaya koersifitas induksi, HcB (kOe), gaya koersifitas polarisasi, HcJ (kOe), kuat medan remanen kiri, Hknee (kOe), produk energi maksimum, BHmax (MGOe), kuat medan produk energi maksimum, Ha (kOe), magnetik fluks, Ba (kG), kuat medan maksimum, Hmax (kOe). Sebelum menentukan nilai ketidakpastian dengan permagraph terlebih dahulu ditentukan nilai ketidakpastian dengan alat penunjang, yaitu jangka sorong dan neraca analitik. Selanjutnya akan didapat nilai ketidakpastian gabungan. Metoda ketidakpastian yang digunakan adalah dengan cara statistik dan berlaku hanya untuk serangkaian observasi. Penentuan nilai ketidakpastian dilakukan dengan cara melakukan pengukuran yang berulang sebanyak sepuluh kali terhadap sample yang sama. Metoda ini mengacu kepada ISO GUM dengan menggunakan evaluasi tipe A. Nilai ketidakpastian yang didapat untuk pengukuran dengan jangka sorong adalah ±0,0329 cm, neraca analitik ±0,0528 gr, dan untuk karakteristik magnet Br ±0,0648 kG, HcB ±0,0632 kOe, HcJ ±0,0628 kOe, Hknee ±0,0643 kOe, BHmax ±0,0631 MGOe, Ha ±0,1213 kOe, Ba ±0,0664 kG,Hmax ±0,0627 kOe.

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Metal oxide semiconductor has attracted so much attention due to its high carrier mobility. Herein, thermoelectric study of nanocrystalline SnO2 through a simple co-precipitation method is conducted to enhance the Seebeck coefficient (S). X-ray diffraction, thermogravimetric analysis (TGA), resistivity (r), Seebeck coefficient (S), and power factor (PF) measurements are conducted to analyze the thermoelectric properties of the material. The measurements show that there are two interesting results, which are the unusual resistivity behavior and the high value of the S. Resistivity behavior shows a non-reflective intermediate semiconductor-metals behavior where the turning point occurs at 250 o C. This behavior is strongly correlated to the surface oxide reaction due to annealing temperature. The maximum S likely occurs at 250 ºC, since the curve shows a slight thermopower peak at 250 ºC. The value of the S is quite high with around twenty times higher than other publications about SnO2 thermoelectric material, this happens due to the bandgap broadening. The energy gap of SnO2 calculated using density functional theory (DFT), which was performed by Quantum Espresso 6.6. The result shows that there is a broadening energy gap at different momentum or wave factor. Nanocrystalline semiconductors material is giving an impact to increase the width of bandgap due to quantum confinement and could enhance the thermopower especially in SnO2 nanocrystalline

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Abstract. Magnetic properties of barium ferrite that were mashed by High Energy Milling (HEM) has been characterized. The starting iron oxide powder (Fe2O3) and barium carbonate (BaCO3) were prepared by powder metallurgy technique by the stages of mixing, calcining, milling, compacting, and sintering. Weight ratio of Fe2O3: BaCO3 was 88.74 wt% : 17.52 wt%. Some additives such as calcium oxide (CaO), silicon dioxide (SiO2), and polyvinyl alcohol (PVA) were added after calcining process. Milling by HEM was varied at 30, 60, 90, 120, and 150 minutes. The ball and container of HEM were made of stainless steel. Characterization micro structure by SEM showed that the milling time affect the grain size of the magnetic powder. The longer of milling time, the grain size was smaller and uniform. Characterization by using magnetic instrument Permagraph showed that the grain size will affect the magnetic properties of barium ferrite. Induction of remanence (Br), coercivity (HcJ), and product energy maximum (BHmax) values increased with increasing milling time. The optimal magnetic properties were obtained at the time of milling 120 minutes with value of Hc = 1.97 kG, HcJ = 2.314 kOe, and BHmax = 0.64 MGOe.

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This study aims to evaluate the structural, magnetic, and microwave absorbing properties at the X-band region of oxidized mill scales as by-product derived from a steel making process by means of a facile solid-state reaction. The oxidized mill scales were heated at 600 °C for 4 h followed by mixing with NiO. A calcination process took place at 900 °C and sintering process were conducted at 1260 °C with a milling process conducted in between the heating process. X-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) were employed to evaluate the structural properties of the Ni-ferrites samples. Remacomp measurement were conducted to evaluate the magnetic properties and vector network analyzer (VNA) to measure its microwave properties. A single phase of NiFe2O4 was confirmed by XRD data. The site occupancies derived from the Rietveld refinement shows that the Ni:Fe:O ratio deviates from the 1:2:4 ratio as that suggests vacancies formed in the Ni2+ and Fe3+ that lowers the unit cell density to 5.08 g/cm3 that further confirmed by EDS measurement. The coercivity of 11 kOe is also higher than the bulk NiFe2O4¬ prepared by the chemical grade raw materials. The reflection data of the microwave properties at X-band of 8-12 GHz do not shows significant absorptions. This study suggests that the selected preparation method yields a single phase, however with the significant crystallographic defects and has less ‘soft’ magnetic properties compared to NiFe2O4 prepared using chemical grade by previous study.