Physical and Microwave Absorption Characteristics of High Powered Ultrasonically Irradiated Crystalline BaFe9Mn1.5Ti1.5O19 Particles

Barium hexaferrite (BHF) with the chemical formula BaFe₁₂O₁₉ is a well-known permanent magnet and is still primarily used in various electrical devices. Because of its excellent magnetic properties, BHF is potentially one of the best candidates as a microwave absorber. For this investigation, the magnetic and microwave absorption characteristics of nanostructured BHF and BaFe₉Mn_1.5Ti_1.5O₁₉ were study. The high coercivity of BHF was substantially reduced through Mn-Ti partial substitution for Fe atoms with a minor reduction of its saturation magnetization. Nanostructured Mn-Ti–doped BHF was obtained through particle size reduction with high-powered ultrasonic irradiation. After 12 h of ultrasonic irradiation, the mean particle of BHF reduced to 61 nm from 380 nm, and the Mn-Ti–doped BHF reduced from 545 nm to 95 nm. The mean crystallite size of the two samples was 15 and 18 nm, respectively. Hence, the particles of both samples contained only a few crystallites. The characterization of reflection loss revealed that the highest absorption value achieved by the nanostructured BaFe₉Mn_1.5Ti_1.5O₁₉ sample was 19.75 dB at 13.6 GHz, and approximately 90% of the intensity of incoming electromagnetic waves was reduced by the material.

Barium hexaferrite; Mechanical alloying; Reflection loss; Ultrasonic irradiation

      Barium hexaferrite (BHF) is a permanent magnetic material characterized by high values of coercivity, saturation magnetization, magnetic transition temperature, and corrosion resistance (Kerschl et al., 2002). The high value of saturation magnetization in BHF provides an opportunity for employing it in microwave absorption applications. However, its high coercivity must be reduced to some extent to facilitate the interaction between the magnetic field of electromagnetic waves and the magnetization of BHF. The reduced coercivity of Mn-Ti–substituted BHF was shown to increase microwave absorption (Manaf et al., 2017). Studies have shown that BaFe_12-yMn_yTi_yO₁₉ (y = 0.0; 0.5; 1.0; 1.5) with y = 1.5 was the best absorption up to a 40 dB reflection loss in 1–5 GHz (Priyono and Manaf, 2009). BHF as an electromagnetic wave absorber is widely used in many applications like information, communication using electronics components, and radar­-absorbing material (Priyono and Manaf, 2009; Adi et al., 2017; Fitriana et al., 2017; Manaf et al., 2017).

Mechanical alloying is a simple tool for the preparation of crystalline materials. Mn-Ti–substituted BHF has been employed by several researchers to prepare microwave absorption materials. Large crystallites resulting from mechanical alloying can be further fragmented to smaller sizes of crystallites by means of high-powered ultrasonic irradiation. There have been several methods available for the fabrication of nanoparticles, including salt-assisted ultrasonic spray pyrolysis (Hwan An et al., 2014), microwave-induced combustion (Fu et al., 2003), ceramic routing (Hessien et al., 2007), microwave-hydrothermal (Sadhana et al., 2012), and citrate sol–gel combustion routing (Sözeri et al., 2012). Mechanical alloying has some advantages: it is a simple technique, produces waste-free material, and can be implemented on a large scale.

In terms of magnetic properties, remanence and coercivity are affected by crystallite size. Magnetic materials with nanostructures allow the grain exchange interaction effect, resulting in enhanced remanence and reduced coercivity (Manaf et al., 1993). The effect is further beneficial for microwave absorption applications since nanoscale crystallites have become a center for electromagnetic wave scattering due to a high density of surfaces in the material. A combination of high remanence and nanostructure would be a potentially powerful source for electromagnetic wave absorption.

        In this work, we explored the potential of BHF and its physical effects on its magnetic properties and microwave absorption characteristics. BHF-based magnetic materials were fabricated through mechanical alloying combined with high-powered ultrasonic irradiation. The material under study is BaFe₉Mn_1.5Ti_1.5O₁₉, a selected composition from the BaFe_12-yMn_yTi_yO₁₉ (y = 0.0, 0.5, 1.0, and 1.5) series, which has been previously studied (Priyono and Manaf, 2009; Repi and Manaf, 2012; Manawan et al., 2014). However, the focus of the current work of this composition is to further explore its excellent absorption characteristics.

Ultrasonic irradiation treatment to the mechanically alloyed BHF and BFMTO powders for 12 h resulted in monocrystalline powders with mean sizes of 15 and 18 nm, respectively. The BHF sample with a mean crystallite size of 15 nm allowed inter-grain exchange interaction, leading to a remanence-to-saturation ratio value of greater than 0.5. The BFMTOU12 sample with the mean crystallite size of 18 nm was characterized by a high RL value, where almost 90% of the incoming EM wave intensity was absorbed by the material.

Research work was funded by Sultan Ageng Tirtayasa University. The authors are grateful to the support of the Physics Department, Universitas Indonesia, for the research facilities.

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