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.

Absorber; Electromagnetic wave; Lanthanum manganite; Magnetic; Perovskite; Substitution; Structural

topic (Eswaraiah et al., 2011). Introducing materials that can absorb electromagnetic waves is an alternative solution to eliminating EMI effects. Some materials, such as radar absorbing materials (RAM) (Mohit et al., 2014), have been reported to exhibit electromagnetic absorption characteristics (Song et al., 2010; Mohit et al., 2014; Sunny et al., 2010) even in the microwave frequency range. To be used in this capacity, electromagnetic wave absorbers must possess the following intrinsic characteristics: permeability (magnetic loss properties) and permittivity (dielectric loss properties). Other characteristics, such as microstructure, thickness, and surface morphology, also determine the absorbing performance of absorber materials. Some studies have reported on absorbers based on doped ferrite magnetic materials (Adi & Manaf, 2012; Duggal & Aul, 2014; Kiani et al., 2014). Likewise, absorbers based on doped dielectric properties have also been found to have absorbing characteristics (Mohit et al., 2014), and tuneable electromagnetic wave absorbers based on combined magnetic and dielectric properties through a composite structure have also been developed (Sunny et al., 2010).

Manganite-based perovskite is another electromagnetic wave absorbing material that has been also developed (Zhang & Cao, 2012; Zhou et al., 2009; Cheng et al., 2010). Manganite-based perovskite is one of the potential candidate materials for microwave absorber applications due to its high permittivity and permeability. Zhang & Cao (2012) succeeded in synthesizing transition metal (TM)-doped La_0.7Sr_0.3Mn_1?xTM_xO_3±? (TM: Fe, Co, or Ni) for microwave absorbing materials. La_0.7Sr_0.3Mn_0.8Fe_0.2O_3±? has shown good properties for microwave absorption. The maximum reflection loss was 27.67 dB at a 10.97 GHz frequency, which was obtained from a sample thickness of 2mm. The absorption bandwidth was above 6 dB at a frequency 6.80 GHz (Zhang & Cao, 2012). Additionally, Zhou et al. (2009) reported the successful synthesis of a modified of manganite-based compound. The Mn substituted lanthanum manganite compound composed of La_0.8Sr_0.2Mn_1-yFe_yO₃ (00.8Sr_0.2Mn_1-yFe_yO₃ (00.8Sr_0.2Mn_1-yFe_yO₃ (03+–O–Mn⁴⁺, causing a break point on the electronic channel resulting in the reduction of the number of hopping electrons (Zhou et al., 2009).

An LaMnO₃ system has high permittivity, but low permeability (Mondal et al., 2006). In a previous report (Sardjono & Adi, 2014), barium substituted La_0.8Ba_0.2MnO₃was shown to have ferromagnetic behavior in which the permeability of the material increased. However, the increase in the absorption bandwidth was still relatively low; it only ranged from ~6.5 dB to ~3 dB at a frequency of 14.2 GHz. In this paper, we report on the results of manganite-based materials with La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x) O₃ (x = 0.1.–0.8) compositions, which were synthesized using a mechanical alloying process. The presence of Ba, Fe, and Ti in the compound should affect the amount of Mn³⁺/Mn⁴⁺ coupling; these significantly contribute to the material’s magnetic properties thereby increasing its permeability. Therefore, the present study aimed to investigate the nature of the coupling-order parameters and the magnetic properties that are exhibited by this manganite-based compound. The results and discussion focused on the synthesis and characterization of Mn-Ti-doped lanthanum manganite of the perovskite system. This paper discusses the changes in the parameters of the crystal structure, microstructure, magnetic properties, and microwave characterization of this material.

The La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1–0.8) materials were synthesized by a solid reaction method using a mechanical milling technique. This material consisted of a mixture of La₂O_3, BaCO₃, Fe₂O₃, MnCO₃, and TiO₂, obtained from Merck, with purity (> 99%). The mixture was milled using a high-energy milling (HEM) SPEX 8000 mixer for 10h. The mixture was compacted into pellet shape using 5000 psi of pressure, and then it was sintered in the furnace at 1000°C in the air for 5h and cooled naturally in the furnace.

The phases were identified using the Rigaku MiniFlex X-ray diffractometer (XRD) with an X-ray tube of CuKa. The radiation wave length (CuKa) was 1.5406 Å. The diffraction angles, ranging from 20° to 80°, were measured using continuous scan mode and a step size of 0.02^o. The Rietveld analysis was performed using General Structure Analysis System (GSAS) software. The pseudo-Voigt function was used to describe the diffraction line profiles at refinement of the geometry profile (Idris & Osman, 2013). The surface morphology and elemental identification of the sample were analyzed, respectively, using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) (JED 2300, JEOL). The magnetic properties were measured using a vibrating sample magnetometer (VSM) (VSM1.2H, Oxford). The reflection and transmission of the electromagnetic waves were measured using a vector network analyzer (VNA) (R3770, Advantest) with a frequency range specification of 300 kHz–20 GHz. However, the analysis of the reflection and transmission testing result was only performed at a frequency ranging from9 GHz to 15 GHz with a sample diameter of 25 mm and a thickness of 1.5 mm.

The phase identification results for the La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1–0.8) samples, measured using XRD, are shown in Figure 1.

Figure 1 XRD patterns of theLa_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1–0.8) samples

The qualitative analysis of the XRD patterns refers to the crystallography open database (COD) with card numbers (COD: 1001820), (COD: 2002196), (COD: 1008841), and (COD: 5910030), respectively, for the phases of LaMnO₃, La₂Ti₂O₇, BaFe₁₂O₁₉, and BaO (Figure 1). As seen, the sample with the doping concentration compositions of x = 0.2 and x = 0.3 formed peaks that are believed to be a single phase of LaMnO₃. However, some foreign peaks were observed in the samples with the doping concentration compositions of x < 0.2 and x > 0.3, which means that the samples contain multi-phases. The composition of the x < 0.2 doping concentrationsample consisted of two phases: LaMnO₃ and La₂Ti₂O₇. The composition of the x > 0.3 doping concentration sample consisted of three phases: LaMnO₃, BaFe₁₂O₁₉, and BaO.

Figure 2  XRD pattern  refinement results fortheLa_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1, 0.3, 0.4, and 0.8) samples

The calculation resulting from the Goldschmidt’s tolerance factor showed that the maximum doping concentration of the Ti and Fe substituted into the Mn atom are only around x~0.4 and x~0.3, respectively. Thus, the rest of the components can alter the crystal structure of the material. The crystal structure analysis conducted using GSAS software was required to determine changes in the crystal structure parameters, the amount of mass fraction formed, and the cationic distribution resulting from the substitution of Fe and Ti into the Mn atom, as shown in Figure 2. Figure 2 shows the refinement X-ray diffraction (XRD) pattern on the samples of La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1, 0.3, 0.4, and 0.8).

The XRD pattern refinement results forthe La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1–0.8) sampleshave a very good quality and meet the criteria of fit R_wp (R_wp< 10%) and the goodness of fit ?² (chi-squared of 1 < ?²< 1.3) (Idris & Osman, 2013). Analysis of the crystal structure was only conducted on the sample with the x = 0.1 doping composition, which represents x < 0.2 and x = 0.3, and the samples with thex = 0.4 and x = 0.8 compositions, which represents x > 0.3. The analysis results for the other compositions are summarized in detail in Table 1.

Results in Table 1 show that La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1–0.8) samples with La_0.8Ba_0.2MnO₃; x=0.2 or La_0.8Ba_0.2Fe_0.2Mn_0.4Ti_0.4O₃ and x=0.3 or  La_0.8Ba_0.2Fe_0.3Mn_0.35Ti_0.35O₃ are a single phase materials. A single phase sample with La_0.8Ba_0.2Fe_0.2Mn_0.4Ti_0.4O₃ composition was also previously reported  (Manaf & Adi, 2014). Hence, Mn ion in La_0.8Ba_0.2MnO₃ has been successfully substituted partially by Fe and Ti ions. However, it is noted that sample with x > 0 exhibited the increase in unit cell volume over that of non doped LaMnO₃ (239.68 ų). When x = 0.1 a steep increase in the unit cell volume of doped LaMnO₃ phase ( 243.13 ų) occured before a continuous decrease along with an increase in x up to 0.8 ( 240.57 ų). Based on the analysis of changes in the volume of the unit cell, it appears that expansion of the unit cell volume for the LaMnO₃ phase occurred in the doping concentrations ranging from x = 0.1 to x = 0.3. Thus,  the Mn atom was succesfully substituted by Fe and Ti. The expansion of the unit cell volume for the LaMnO₃ phase looks very large because, for the doping concentration of x = 0.1, the biggest substitution is Ti, which has a  radii (r = 2.0 Å) larger than the radii of the Mn atom (r = 1.79 Å). The volume of the unit cell of this LaMnO₃ phase gradually decreases with increasing doping concentration, which means the content of Ti decreased and the content of Fe increased. The addition of the doping concentration (x > 0.3) results in an imbalance inthe reaction; thus there is anexcess of Fe, so Fe prefers to bind to Ba to form barium hexaferrite. Because the composition of these compounds is relatively stable, no change in the unit cell volume is seen forthe BaFe₁₂O₁₉ phase.

Table 1 Detail summary of the refinement results for the crystal structure parameters of the La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x = 0.1–0.8)

Materials with designated La_0.8Ba_0.2Fe_xMn_½(1-x)Ti_½(1-x)O₃ (x=0.1–0.8) composition were successfully synthesized through the mechanical alloying process. The LaMnO₃ based phase is being the major phase in all samples with the highest mass fraction up to 99 % found in samples with x < 0.3. All samples contained hard magnetic BaFe₁₂O₁₉ phase. The microwave absorbing properties of sample with x= 0.3 is the highest among the samples. The electromagnetic wave absorption reaches 95% at the highest peak frequency 14.1 GHz in the sample of x = 0.3 having sample thickness of relatively thin about 1.5 mm.

This work wassupported by the Program for Research and Development of smart magnetic material (DIPA 2015), the Center for Science and Technology of Advanced Materials, and the National Nuclear Energy Agency. Many thanks to Dra. Mujamilah, M.Sc. for her kind help in characterizing the use of VSM.

Adi, W.A., Manaf, A., 2012. Structural and Absorption Characteristics of Mn-Ti Substituted Ba-Sr Hexaferrite Synthesized by Mechanical Alloying Route. Journal of Basic and Applied Scientific Research, Volume 2(8), pp. 7826–7834

Cheng, Y.L., Dai, J.M., Wu, D.J., Sun, Y.P., 2010. Electromagnetic and Microwave Absorption Properties of Carbonyl Iron/La_0.6Sr_0.4MnO₃Composites. Journal of Magnetism and Magnetic Materials, Volume 322, pp. 97–101

Duggal, S., Aul, G.D., 2014. Review on Effect of Electric Permittivity and Magnetic Permeability over Microwave Absorbing Materials at Low Frequencies. International Journal of Engineering and Advanced Technology, Volume 3(5), pp. 12–19

Eswaraiah, V., Sankaranarayanan, V., Ramaprabhu, S.,  2011. Functionalized Graphene–PVDF Foam Composites for EMI Shielding. Macromolecular Materials and Engineering, Volume 296, pp. 1–5

Idris, M.S., Osman, R.A.M., 2013. Structure Refinement Strategy of Li-based Complex Oxides using GSAS-EXPGUI Software Package. Advanced Materials Research, Volume 795, pp. 479–482

Kiani, E., Rozatian, A.S.H., Yousefi, M.H., 2014. Structural, Magnetic and Microwave Absorption Properties of SrFe_12–2x(Mn_0.5Cd_0.5Zr)_xO₁₉Ferrite. Journal of Magnetism and Magnetic Materials, Volume 361, pp. 25–29

Manaf, A., Adi, W.A, 2014. Structural Investigation and Microwave Characteristics of (Ba_0.2La_0.8)Fe_0.2Mn_0.4Ti_0.4O₃ Absorbing Materials. In: AIP Conference Proceedings 1589, pp. 249–252

Mohit, K., Vibha R.G., Sanjeeb, K.R., 2014. Microwave Dielectric Properties of Ni_0.2Cu_xZn_0.8-xFe₂O₄ for Application in Antenna. Progress in Electromagnetics Research B, Volume 57, pp. 157–175

Mondal, P., Bhattacharya, D., Choudhury, P., 2006. Dielectric Anomaly at the Orbital Order–disorder Transition in LaMnO3+?. Journal of Physics: Condensed Matter, Volume 18(29), pp. 6869–6881

Sardjono, P., Adi, W.A., 2014. Thermal Analysis and Magnetic Properties of Lanthanum Barium Manganite Perovskite. Journal of Advanced Materials Research, Volume 896, pp. 381–384

Song, J., Wang, L., Xu, N., Zhang, Q., 2010. Microwave Absorbing Properties of Magnesium-substituted MnZn Ferrites Prepared by Citrate-EDTA Complexing Method. Journal of Materials Science & Technology, Volume 26(9), pp. 787–792

Sunny, V., Kurian, P., Mohanan, P., Joy, P.A., Anantharaman, M.R., 2010. A Flexible Microwave Absorber Based on Nickel Ferrite Nanocomposite. Journal of Alloys and Compounds, Volume 489, pp. 297–303

Wu, Z., Li, M., 2011. Electromagnetic Interference Shielding of Carbon Nanotube Macrofilms. Scripta Material, Volume 64, pp. 809–812

Zhang, S., Cao, Q., 2012. Electromagnetic and Microwave Absorption Performance of Some Transition Metal Doped La_0.7Sr_0.3Mn_1?xTM_xO_3±? (TM = Fe, Co or Ni). Materials Science and Engineering B, Volume 177, pp.678–684

Zhou, K.S., Xia, H., Huang, K.-L., Deng, L.-W., Wang, D., Zhou, Y.-P., Gao, S.-H., 2009. The Microwave Absorption Properties of La_0.8Sr_0.2Mn_1-yFe_yO₃Nanocrystalline Powders in the Frequency Range 2–18 GHz. Physica B: Condensed Matter, Volume 404, pp. 175–179