M-type hexaferrite, with chemical formula of MeFe12O19 (Me = Ba, Sr and Pb) have been widely used as permanent magnet with great technical importance attracted an extensive attention for the last few decades. The increase in electromagnetic pollution due to the rapid development of gigahertz (GHz) electronic systems and telecommunications has resulted in a growing and intense interest in electromagnetic-absorber technology. Electromagnetic interference (EMI) can cause severe interruption of electronically controlled systems. It can cause device malfunctions, generate false images, increase clutter on radar and reduce performance because of system-to-system coupling. Recent developments in Microwave absorber technology have resulted in materials that can effectively reduce the reflection of electromagnetic signals on the one hand, and have good physical performance and lower production cost on the other. There have been several reports regarding the use of ferrite materials for microwave absorbers. Spinel Mn-Zn type ferrite magnet is now widely used for application in microwave with lower frequencies (1-3 GHz). As compared to the usual spinel ferrites, the hexaferrites with planar magnetic anisotropy are of great interest for use as electromagnetic energy dissipation in the GHz range. Barium ferrite powders are ideal fillers for the development of electromagnetic attenuation materials at microwave, due to their low cost, low density, high stability, large electrical resistivity and high microwave magnetic loss. Whereas Garnet type is used for the applications in higher frequencies ( ~ 6 GHz) . Even much higher frequencies absorber materials such as Radar employing hexagonal magnetic ferrites like SrFe12O19. Recently, several techniques have been developed to prepare intrinsic and doped hexagonal ferrites for recoding application and for microwave devices.
Latest research has been conducted by Tri Wahono and Azwar Manaf from Materials Science, Department of Mathematic and Natural Science, University of Indonesia, Indonesia. They are report on the relationship between magnetic properties and microstructure for SrO.6Fe2-(x+y)MnxTiyO3 .
Strontium hexaferrite with nominal compositions SrO.6Fe2–(x+y) MnxTiyO3 (x = 0, y =0; x = 0.4, y = 0.6; x = 0.5, y = 0.5; x = 0.6, y = 0.4) have been synthesized by solid state reaction (mechanical milling). The four component powders were SrCO3, Fe2O3, MnCO3, and TiO2 mixed with High Energy Milling for 10 hours and sintered at 1050°C in the air at atmosphere pressure for 15 hour and furnace cooling. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), vibrating sample magnetometer (VSM) and vector network analyzer were used to analyze its structure, electromagnetic and Microwave Absorption Properties. The result showed that, phase identification by refinement results of XRD pattern confirmed single phase was obtained for Mn-Ti substituted SrO.6Fe2O3 with x = y and multiphase formed for x ¹ y. The microstructure analyses by SEM showed that the varied particle sizes of 2 ~ 5 mm. Evaluation on the magnetic characteristic indicated that coercivity decreased as the number of Mn2+ and Ti4+ ions increased but significant decrease in saturation magnetization obtained for Mn and Ti substitution with x ¹ y. Present investigation demonstrates that microwave absorber, reflection and transmission as well as reflection loss in the frequency range 7–16 GHz were derived. Absorption performance of Mn and Ti substituted strontium hexaferrite are also reported.