Abstract. Ba 0.6 Sr 0.4 Fe 12-z Mn z O 19 (z = 0,1,2, and 3) were successfully synthesized by solid state reaction through a mechanical milling method. Stoichiometric quantities of analytical-grade MnCO 3 , BaCO 3 , Fe 2 O 3 , and SrCO 3 precursors with purity greater than 99% were mixed. It was found that the best phase composition, having an absorber with high performance, was Ba 0.6 Sr 0.4 Fe 11 MnO 19 . Refinement of the X-ray diffraction patterns revealed that the Ba 0.6 Sr 0.4 Fe 11 MnO 19 was single-phase and had a hexagonal structure (P63/mmc). Mechanical milling of Ba 0.6 Sr 0.4 Fe 11 MnO 19 powders produced particles with a mean size of ~850 nm. SEM images revealed the morphology of the particles as being aggregates of fine grains. The magnetic properties of the Ba 0.6 Sr 0.4 Fe 11 MnO 19 particles showed a low coercivity and a high remanent magnetization. The Ba 0.6 Sr 0.4 Fe 11 MnO 19 has certain microwave absorber properties in the frequency range of 8-14 GHz, with an absorbing peak value of -8 dB and -10 dB at frequencies of 8.5 and 12.5 GHz, respectively. The study concludes that the Ba 0.6 Sr 0.4 Fe 12-zMnzO 19 that was successfully synthesized is a good candidate for use as an electromagnetic absorber material.

Nickel ferrite (NixFe3-xO4) have been synthesized using solid state reaction with composition (2x)NiO : (3-x)Fe2O3 (x = 0.5; 1.0; 1.5 dan 2.0) in mol in wt%. Mixing of this powder was milled with HEM (High Energy Milling) for 10 hours, and then sintered at 1000 °C for 3 h. X-ray diffraction pattern indicates that the all of samples are single phase in this stage. FTIR (Fourier transform infrared) analysis showed two absorption bands in the range of ~410 - ~600 cm-1 related to octahedral and tetrahedral sites. The magnetic measurement using vibrating sample magnetometer (VSM) shows that the sample exhibited a ferromagnetic behaviour with its coercivity value in the range of 164-217 Oe, and the maximum value wasshowed by x =1.5. VNA (Vector Network Analyzer) characterization shows the ability electromagnetic wave absorption with RL (reflection loss) value of -28 dB occurs at frequency of 10.98 GHz. It means that the Ni1.5Fe1.5O4 sample can absorb microwave about ~96 % at 10.98 GHz.

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A magnetic Fe 3 O 4 @ZnO nanocomposite (NC) was successfully synthesized by a wet milling method using a high energy milling (HEM) machine. The magnetic Fe 3 O 4 @ZnO NC was characterized by an X-ray Diffractometer (XRD), scanning and transmission electron microscopes (SEM and TEM), and a vibrating sample magnetometer (VSM @ZnO NC under UV irradiation were quantified by the degradation of a methylene blue (MB) dye solution. The result reveals that the photodegradation efficiency of Fe 3 O 4 @ZnO NC is favorable at pH neutral (pH = 7) reaching 100%. By increasing the MB dye concentration from 10 ppm to 40 ppm, the photodegradation efficiency decreases from 100% to 52%. The Fe 3 O 4 @ZnO NC can be easily collected by an external magnet. The magnetic Fe 3 O 4 @ZnO NC could be extended to various potential applications, such as purification processes, catalysis, separation, and photodegradation.

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This paper reports on the magnetic properties and electromagnetic characterization of La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1-0.8). The La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1-0.8) materials were prepared using a mechanical alloying method. All the materials were made of analytical grade precursors of BaCO3, Fe2O3, MnCO3, TiO2, and La2O3, which were blended and mechanically milled in a planetary ball mill for 10h. The milled powders were compacted and subsequently sintered at 1000°C for 5h. All the sintered samples showed a fully crystalline structure, as confirmed using an X-ray diffractometer. It is shown that all samples consisted of LaMnO3 based as the major phase with the highest mass fraction up to 99% found in samples with x < 0.3. The mass fraction of main phase in doped samples decreased in samples with x > 0.3. The hysteresis loop derived from magnetic properties measurement confirmed the present of hard magnetic BaFe12O19 phase in all La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1-0.8) samples. The results of the electromagnetic wave absorption indicated that there were three absorption peaks of ~9 dB, ~8 dB, and ~23.5 dB, respectively, at respective frequencies of 9.9 GHz, 12.0 GHz, and 14.1 GHz. After calculations of reflection loss formula, the electromagnetic wave absorption was found to reach 95% at the highest peak frequency of 14.1 GHz with a sample thickness of around 1.5 mm. Thus, this study successfully synthesized a single phase of La0.8Ba0.2FexMn½(1-x)Ti½(1-x)O3 (x = 0.1-0.8) for the electromagnetic waves absorber material application.

Objective: This study investigated effects of heat treatment on the crystallinity and phase composition of hydroxyapatites (HAs) of different heat treatment.Methods: HA powder was synthesized by the chemical precipitation method based on the reaction between the phosphorous acid and calcium hydroxide. Synthesized HA was divided into three groups for which each group was then given heat treatment at 100°C, 900°C, or 1300ºC. Phase identification, analyses and the crystallinity of the synthesized HAs were determined using the X-ray diffraction coupled with the Rietveld refinement. Results:The synthesized HAs with each heat treatment were identified as HA phase containing hexagonal structure. Those treated at 100°C or 900°C revealed with crystallinity of 48% and 68%, respectively, with no additional phase; whereas, those treated at 1300°C produced a crystallinity of 72% and contained dicalcium and tricalcium phosphates. Conclusion:The synthesized HAs treated at 100°C, 900°C, or 1300°C were HA phase with hexagonal structure. The variable crystallinity of the synthesized HAs yielded from different heat treatment temperature correspondingly determines different phase composition.

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