Enhancement in Optical Properties of Lanthanum-Doped Manganese Barium Hexaferrites under Different Substitutions

The permeability and electrical resistivity of barium hexaferrite magnetic materials can be used in various products such as magnetic recording media, computers, electronic devices, materials for permanent magnets, and communication devices. This work focuses on the synthesis of rare earth lanthanum (La 3+ )-doped manganese in barium hexaferrite (Ba 1 − x La x Mn y Fe 12 − y O 19 ) ( x � 0.02–0.10 and y � 0.02–0.10) prepared by using the coprecipitation method. The intensity peak is increased with increasing the concentration of lanthanum, which shows the enhancement in the degree of crystallinity and increase in the size of crystallite. The band gap energy decreased gradually with the increase of concentration of lanthanum. The micrographs observed that the material is basically made up of some rings or rods such as particles in pure La-Ma in barium hexaferrite. The agglomeration was observed because of heat behavior at 600 ° C or may be concentration eﬀect. The structural studies are done using X-ray diﬀraction, UV, FT-IR, and


Introduction
e barium hexaferrite (BaFe 12 O 19 ) has been widely used as permanent magnetic materials. e microwave-absorbing materials have been used in military and the civil technology, such as garnet and spinel ferrites [1]. e permeability and electrical resistivity barium hexaferrite magnetic materials can be used in various products such as magnetic recording media, computers, electronic devices, materials for permanent magnets, and communication devices [2,3]. e barium hexaferrite is very important for industrial use. e nanoparticles of barium hexaferrite have large saturation magnetization, high electrical resistivity, large uniaxial magnetic anisotropy, chemical strength, high curie temperature, and high coerciveness because their compounds can also be used at high frequency as correlated spinel ferrites and garnet [4,5]. e electromagnetic compatibility used for special sensitive equipment in the application of hexagonal ferrites and compounds is based on great possibility as materials for higher electromagnetic frequency [6].
ere are some materials exist together between ferroelectric and ferromagnetism. To reform intrinsic magnetic properties of hexaferrites, it can be achieved by using various techniques including doping of La-Mn for Ba or Fe or both sublattices [7]. e barium hexaferrite is used in the fabrication of equipment and plays an important role in the improvement of technology and industrial products. Depending on magnetic behavior, the magnetic materials are categorized into ferromagnetic, diamagnetic, and paramagnetic materials. Ferrites made a cubic structure, but some ferrites made hexagonal crystal structure also known as hexaferrites [4] [8][9][10].
e unit cell of M-type hexaferrite contains 2 barium ions and 24 ferric and 38 oxygen ions. In the unit cell, the 24 ferric ions occupy five distinct sites, such as 2a, 2b, 4f 1 , 4f 2 , and 12k. e crystal structure of 4f1 is tetrahedral, 2b-formed trigonal, and 12k, 2a, and 4f 2 are octahedral sites [11]. e substitution of ions at different positions in the crystal structure and magnetic moment depends on the electronic arrangement of the atoms [12].
e Fe 3+ ions have their spins parallel to the crystallographic c-axis in the 2a (↑), 2b (↑), and 12k (↑) sites, whereas 4f 1 (↓) and 4f 2 (↓) sites have opposite direction. e sublattices (2a, 2b, and 12k) and (4f 1 and 4f 2 ) are parallel and antiparallel to the hexagonal c-axis [13]. Ferroelectric and ferromagnetism coexist in very few materials. e substitution of diamagnetic cations in barium hexaferrite has large spontaneous multiferric and magnetoelectric effect and polarization property at room temperature [6]. Keeping this in mind, we have designed this study to synthesize lanthanum manganese barium hexaferrite nanoparticles with different lanthanum precursor concentrations and studied its effect on the optical properties.
e solution was mixed with precipitate agent (NaOH) to obtain less chemically dispersion of nanoparticles and then further stirred at 100°C for 90 minutes to changing of hydroxide (OH − ) into ferrites. During stirring, the addition of NaOH (drop wise) in solution helps to maintain the PH 12 throughout the reaction. As the stirring was stopped, the PH was approached at 12. After that, samples had kept for aging whole night. Once the reaction process completed, the precipitates present in the solution are settled down and ready to collect. To remove the impurities, collected precipitates were washed several times with distal water, and sodium and hydrogen ions are removed. e sample was places in an oven for 12 hours at 90°C. e precipitates were grinded into clear powder form with pestle mortar and then sintered at 600°C in muffle furnace for 3 hours.

Result and Discussion
All the samples were analyzed by XRD analysis. is is the most widely used diffraction method to determine the structure of crystalline solid when X-rays are diffracted not by single crystal but form randomly oriented crystalline particles. ese peak patterns are used for the identification and measurement of different structural phases and parameters. e powder method is the very quick and convenient method to obtain diffraction data and readily applicable to all crystalline materials. e XRD analysis was performed with Cu-Kα (1.5406Å) radiation at ambient temperature for the study of phase structure, lattice parameters, and crystallite size. e XRD pattern of lanthanum- e diffraction peaks were identified by using JCPDS card # 73-1964 and # 44-0206 of the hexagonal crystal structure. e X-ray diffraction of phase purity and crystal structure of Ba 1−x La x Mn y Fe 12−y O 19 hexaferrite were prepared by the lanthanum substitutions. e intensity peaks were changed due to the substitution of lanthanum-doped manganese hexaferrite in crystal structure. e sharp peak (311) moves towards a lower angle to the higher angle as shown in Figure 2. e peak (311) shifted towards a lower angle to the higher angle due to the larger ionic radii of La (2.35Å) and Mn (0.91Å) compared to hexaferrite ions. e lanthanum-doped manganese hexaferrite has hexagonal structure.  [14]: where "D" is the crystalline size, "λ" is the wavelength, "β" is the full width at half maximum, and θ is Bragg's angle. e intensity peak is increased with increasing the concentration of lanthanum, which shows the enhancement in the degree of crystallinity and increase in the size of crystallite. e average sizes of the crystalline samples were determined from the width of peaks by using the Scherrer relation. e average crystalline size was found to be 13.10, 13.61, 14.80, 15.77, and 16.19 nm, shown in Figure 3, for the samples prepared with a lanthanum concentration of 0.02, 0.04, 0.06.0.08, and 0.10 mole, respectively. e value of crystalline size can be seen in Table 1. e lattice parameters "a" and "c" are calculated from the following relation: Here, (hkl) are miller indices, "d" is the interplanar spacing, and "a" and "c" are the lattice constant. e volume of hexagonal structure can be determined from the following formula: where "V" is the volume and "a" and "c" are the lattice constant of hexaferrites. UV-visible absorption and band gap energy of a material are energetic techniques to analyze the optical properties of semiconductor material. For the sample Ba 1−x La x Mn y Fe 12−y O 19 (x � 0.02 to 0.08 and y � 0.2 to 0.8), UV-visible absorption spectra of La-Mn hexaferrite are shown in Figure 4. Figure 4 shows the absorption spectrum of Ba 1−x La x Mn y Fe 12−y O 19 wavelength between 300 and 900 nm in region. e absorbance sharply increases from 0.5 to 1 with the increases in wavelength from 360 nm to 500 nm, and absorbance gradually increases from 1 to 1.15 as the wavelength increases from 500 nm to 900 nm. is peak identifies the inner shell electron transition. ere is a minor peak shifting on both sides towards lower and higher wavelengths which is responsible for the blue and red shifts, respectively. e tangent is drawn in a Tauc plot to find the energy gap which is (1.13 eV, 0.77 eV, 0.74 eV, 0.72 eV, and 0.71 eV) shown in Figure 4. e band gap energies of the La-doped Mn hexaferrite sample are greater than the quixotic energy. By the Tauc plot mode, we determine the information between energy and (αh]) 2 from UV-visible absorption. e plotting of (αh]) 2

vs the photon energy (h]) gives a straight line in a certain region. e Tauc plot equation is
where A is an absorption constant, Eg is the band gap energy, and h] is the photon energy. e c is the type of electronic transition which is 1/2, 2, 3/2, and 3. e c � ½ corresponds to direct band gap of semiconductor materials. is equation is used to calculate the band gap of theoretical energy:   Here, Ab is the absorbance and t is the thickness of the cuvette. e band gap energy (Eg � 1.13 eV, 0.77 eV, 0.74 eV, 0.72 eV, and 0.71 eV) is shown in Table 2, which decreases gradually with the increase of the sample Ba 1x La x Mn y Fe 12−y O 19 (x � 0.02 to 0.10 and y � 0.2 to 0.10) as shown in Figure 5. e band width of conduction and valance bands decrease as the concentration of lanthanum is increased, which results reduced in band gap. In addition, the band gap values decrease with increases in lanthanum concentrations which means the energy levels within the bands are decreased in which each electron required more energy to jump from valance band to conduction band.
Scanning electron microscopy have been performed to study the microsrtrucural and surface properties of Ba1−xLaxMnyFe12−yO19 as shown in Figure 6. e shape of SEM images is irregular cubic, spiral, rings, and rods shown in Figure 6. e micrographs observed that the material is basically made up of some rings or rods such as particles in pure La-Ma in barium hexaferrite (Figure 6(a)), and as the concentration of the lanthanum increases, an increase also occurs in the agglomeration of these particles. e agglomeration was observed because of heat behavior at 600°C or may be concentration effect. Further vacancies of oxygen atom are created by introducing La at Fe +3 sites of barium ferrites. Rate of sintering significantly improves grain size of prepared samples. e cluster formation at higher concentration of lanthanum is due to swapping of paramagnetic and ferromagnetic behavior of lanthanum and

Conclusion
e La-Mn substituted barium hexaferrite with nominal composition Ba 1−x La x Mn y Fe 12−y O 19 (x � 0.02-0.08 and y � 0.2-0.8) has been successfully synthesized using the coprecipitation method. Magnetic properties of La-Mn substituted barium hexaferrites including large magnetic anisotropy, large saturation magnetization, high electrical resistivity, high curie temperature, and good chemical strength by the reason of these compounds can be used at higher frequency as correlated to garnet and spinel ferrites. e structural studies are done using XRD, UV, FT-IR, and SEM techniques. XRD analysis shows pure hexagonal structure. e Scherrer formula was used to calculate the crystalline size of magnetic material. e average crystallite size for the calcined sample was in the range of 13-22 nm. Absorbance of the sample was measured by UV spectroscopy. e energy band gap decreases gradually with the increase of sample concentration. e band width of conduction and valance bands decrease as the concentration of lanthanum is increased, which results reduced in band gap. SEM micrograph images for all compositions represent nonuniform grain size distribution with sharp edges on its surface. e agglomeration has been observed due to heat treatment at 600°C or may be concentration effect. e micrographs observed that the material is basically made up of some rings or rods such as particles in pure La-Ma in barium hexaferrite (Figure 6(a)), and as the concentration of the lanthanum increases, an increase also occurs in the agglomeration of these particles. e FT-IR spectra of the samples were conducted to identify the organic polypyrrole (PPy) and inorganic lean body mass (LBM) elements present in the sample.

Data Availability
e XRD, SEM, FT-IR, and UV data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.