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.

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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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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