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Fe3O4 and Fe3O4/TiO2 magnetic nanoparticles have been successfully prepared using an eco-friendly green synthesis method with various Moringa Oleifera (MO) extract concentrations. The X-ray diffraction and transmission electron microscopy results confirmed that the microstructure of Fe3O4 nanoparticles is a cubic inverse spinel structure with an average particle size of 9.2–11.7 nm and lattice parameters is in the range of 8.14–13.60 Å and the MO did not change the morphological structure of Fe3O4. Fourier-transform infrared showed that the samples had magnetic particles vibration peaks at 632 cm-1 and 570 cm-1, 500–700 cm-1 for Ti-O peaks, and 1047 cm-1 for aromatic C-C indicating green synthesis. Furthermore, the results of UV-VIS data presented the absorption edges of Fe3O4, Fe3O4-MO, and Fe3O4/TiO2-MO were 187.9 nm, 198.7 nm, and 197.1 nm, respectively. The bandgap energy of Fe3O4-MO is in the range of 2.62–2.66 eV and the bandgap energy of Fe3O4/TiO2-MO is 2.76 eV which explains that it depends on the bioactive compounds. Based on these results, the green synthesis nanoparticles have the potential to be applied in the industrial sector, especially for photocatalyst applications.

The giant magnetoresistance (GMR) thin film with spin valve (SV) structure of Ta (2 nm)/Ir20Mn80(10 nm)/Co90Fe10(3 nm)/Cu (2.2 nm)/Co84Fe10B4(10 nm)/Ta (5 nm)] fabricated by RF magnetron sputtering method with a magnetoresistance (MR) of 6% was used in this work. Green synthesis of Fe3O4 magnetic nanoparticles (MNPs) using Moringa Oleifera (MO) leaf extract have been successfully conducted using the coprecipitation method. Fe3O4 MNPs demonstrated the inverse cubic spinel structure with the average crystallite size of 13.8 nm and decreased to 11.8 nm for Fe3O4/PEG. Fe3O4, as a magnetic label, integrated with a Wheatstone bridge-GMR sensor provides access to GMR-based biosensors. The induced-field increase leads the signal (ΔV) to increase with increasing nanoparticle concentration. It was discovered that a sensor can distinguish different types of magnetic labels. The sensitivity for Fe3O4 and MO-green synthesized Fe3O4 magnetic label was 0.04 and 0.1 mV/g/L, respectively. The GMR sensor performed the highest sensitivity on the MO-green synthesized Fe3O4 label. Thus, the SV thin film as a sensor and the green-synthesized Fe3O4 nanoparticles as a superior magnetic label are an excellent combination for biosensor application.

<p>Studi ini mendeskripsikan analisis transisi fasa dan sifat dielektrik pada bahan litium kobalt silikat (Li₂CoSiO₄) yang dipreparasi dari silika sekam padi dan produk daur ulang katoda baterai ion litium bekas dengan perbandingan massa 1:1. Transisi fasa pada sampel Li₂CoSiO₄ dipelajari menggunakan teknik <em>termogravimetry/differential thermal analysis</em> (TG/DTA). Sedangkan, nilai konstanta dielektrik pada sampel yang telah disinter pada suhu 600 – 900 ^oC dikarakterisasi menggunakan <em>i</em><em>nductance</em>, <em>c</em><em>apacitance</em>, dan <em>r</em><em>esistance</em> (LCR) <em>meter</em>. Hasilnya, pada rentang suhu 410 – 850 ^oC terjadi transisi polimorfik fasa  menjadi fasa . Suhu 850 ^oC juga merupakan titik transisi dimana fasa  berubah menjadi fasa . Transisi fasa yang terjadi pada sampel  Li₂CoSiO₄diikuti dengan peningkatan nilai konstanta dielektrik dalam rentang frekuensi 450 – 100.000 Hz.</p><p><strong>Analysis of Phase Transition and Dielectric Properties of Li₂CoSiO₄ Prepared from Rice Husk Silica and The Recycling Product of Used Lithium Ion Batteries Cathode.</strong> This study describes the analysis of the phase transition and dielectric properties of lithium cobalt silicate (Li₂CoSiO₄) prepared from rice husk silica and the recycling product of used lithium ion batteries cathode with mass ratio of 1:1. Phase transition in Li₂CoSiO₄ sample was studied using thermogravimetry/differential thermal analysis (TG/DTA) techniques. Meanwhile, the dielectric constant value in the samples sintered at temperature of 600 – 900 ^oC were characterized using inductance, capacitance, and resistance (LCR) meter. As a result, a polymorphic transition from  phase to  phase was occured in the temperature range of 410 ­– 850 ^oC. Temperature of 850 ^oC is a transition point from  phase to  phase. The phase transitions occured in the Li₂CoSiO₄ was followed by the increasing of the dielectric constant in the frequency range of 450 – 100,000 Hz.</p>