Trends Sci. 2025; 22(12): 11043

The Influence of Yttrium Doping on The Microstructure and Magnetic Properties of Barium Hexaferrite

Nazaruddin Nasution¹, Syahrul Humaidi^1,*, Erna Frida¹, Tulus Na Duma¹,

Phahul Zhemas Zul Nehan², Marzuki Naibaho^2,3 and Masno Ginting³

¹Postgraduate Program (Physics), Fakultas Matematika Dan Ilmu Pengetahuan Alam, Universitas Sumatera Utara, Medan 20155, Indonesia

²Study Program of Materials Science, Department of Physics, Faculty of Mathematics and Natural Science,

Universitas Indonesia, Depok 16424, Indonesia

³Center for Advanced Materials Research (PRMM) - National Research and Innovation Agency (BRIN),

Tangerang-South, Banten 15314, Indonesia

(^*Corresponding author’s e-mail: [email protected])

Received: 24 June 2025, Revised: 2 July 2025, Accepted: 9 July 2025, Published: 30 August 2025

Abstract

This study investigates the effect of Yttrium (Y) addition as a doping element on the microstructure and magnetic properties of barium hexaferrite (BaFe₁₂O₁₉), synthesized using the High Energy Milling (HEM) method. Samples with varying Y concentrations (x = 0.00, 0.05, 0.1 and 0.15) were prepared and characterized using X-ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-ray (SEM-EDX), and Vibrating Sample Magnetometer (VSM). The XRD results showed that all samples exhibited a hexagonal M-type crystal structure with a P63/mmc space group. The addition of Y caused a shift in diffraction peaks toward lower angles, indicating an increase in lattice parameters. SEM morphological analysis revealed a decrease in grain size (D_SEM) with increasing Y content, from 813 nm (x = 0) to 519 nm (x = 0.15). Additionally, magnetic measurements indicated that the sample with x = 0.05 (Y5) had the optimal magnetic properties, with a saturation magnetization (M_S) of 58.11 emu/g and a coercivity (H_C) of 2,715 Oe, making it a promising candidate for microwave absorber applications. This study demonstrates that Y doping can modify the structure and enhance the magnetic properties of barium hexaferrite, particularly in optimizing magnetization and reducing coercivity for microwave absorption applications.

Keywords: BaFe₁₂O₁₉, High energy milling, Magnetic properties, Microwave absober properties, Yttrium doping

Introduction

Magnetic materials have made a significant contribution to the advancement of electronic information technology and manufacturing. One of the technological developments is microwave absorber materials, which aim to (i) reduce electromagnetic wave radiation from electronic devices that may negatively affect human health in the long term, and (ii) enhance stealth radar technology in the military sector [1,2]. Various magnetic materials have been explored to support these applications, including metal oxides, spinel ferrites, hexaferrites, perovskite manganites,

magnetic alloys, and 2D materials [3-6]. Among these materials, hexaferrites present both scientific and technical advantages. These are attributed to their characteristics, such as high Curie temperature, high saturation magnetization, high coercivity, low eddy current losses, high electrical resistivity, excellent corrosion resistance, good chemical stability, low material cost, and ease of production [7-12]. The general formula for M-type hexaferrite with a magnetoplumbite structure is AFe₁₂O₁₉, where A can be Ba, Sr, or Pb [4,13-15].

In addition to their role in hexaferrites, the constituent ions Ba²⁺ and Fe³⁺ are known for their functional versatility in other advanced material systems. Barium has been widely used in polymer composites and dielectric materials due to its thermal and electrical properties [16], while Fe³⁺ plays key roles in flexible electronics, catalysis, and energy storage systems because of its redox activity and multifunctionality [17]. M-type hexaferrites are considered highly suitable for industrial-scale microwave absorber applications. This is supported by the fact that M-type hexaferrites currently dominate up to 57% of permanent magnetic materials [2]. Due to their great potential, the development and exploration of M-type hexaferrites remain a central focus in magnetic material research.

The BaFe₁₂O₁₉ compound has been extensively studied due to its potential applications, particularly as a microwave absorber. Generally, BaFe₁₂O₁₉ has a hexagonal crystal structure containing 64 ions, including both cations and anions, within each unit cell [2]. This crystal structure belongs to the P63/mmc space group, characterized by ions distributed across 11 different symmetry sites. A single unit cell contains 24 Fe³⁺ ions, which are crystallographically located in 3 distinct lattice sites: Tetragonal (4f₁), octahedral (12k, 2a and 4f₂), and trigonal bipyramidal (2b) [11,18]. More specifically, 16 of the Fe³⁺ ions have spins aligned parallel to the crystallographic c-axis, forming the majority spin direction ↑ (12k, 2a and 2b), while the remaining 8 Fe³⁺ ions are aligned in the opposite direction, forming the minority spin direction ↓ (4f₁ and 4f₂) [19]. This unique arrangement allows for the substitution of cations in BaFe₁₂O₁₉ with other elements, aiming to enhance its magnetic properties. Such modifications significantly affect its performance in applications like microwave absorbers by altering its electronic structure, resonance frequency, and atomic magnetization [2,4,20]. Therefore, cation substitution in BaFe₁₂O₁₉ is a promising strategy for improving its functional properties.

Cation substitution in the BaFe_12−xRE_xO₁₉ compound, where RE represents rare earth elements such as Y³⁺, La³⁺, Gd³⁺, Ho³⁺, Er³⁺ and Ce³⁺, can lead to structural changes. These changes include structural distortion, lattice strain, crystallite size, and grain size, all of which can contribute to improvements in magnetic and electronic properties [2,9,21-25]. Hashhash et al. [22] reported a study on cation substitution in the compound Ba_0.5Sr_0.5Fe_11.4R_0.6O₁₉, where R = La, Yb, Sm, Gd, Er, Eu, and Dy. The results showed that substitution with different rare earth elements, each having varying ionic radii, affected key magnetic parameters such as maximum magnetization (M_max), saturation magnetization (M_S), remanent magnetization (M_r), and coercivity (Hc). The highest values of M_max, M_S, and M_r under an applied magnetic field of 2 T were observed in the Ba_0.5Sr_0.5Yb_0.6Fe_11.4O₁₉ compound, with respective values of 59.8, 63.1, and 29.4 emu/g. It was also reported that Yb substitution resulted in the lowest H_C value among the samples, at 2,400 Oe [22]. Similarly, Sanker et al. [2] investigated the effect of Yttrium (Y) substitution in BaFe_12−xY_xO₁₉ compounds with x = 0.0, 0.2, 0.4 and 0.6. They found that at x = 0.2 with a sintering temperature of 1,100 °C, the highest values of M_max, M_S, and M_r were achieved 100.27, 106.00, and 49.86 emu/g, respectively under an applied magnetic field of 2 T. Meanwhile, the H_C value was around 2,389.3 Oe. Based on these 2 studies, it is evident that Y substitution in BaFe₁₂O₁₉ compounds can result in higher M_max, M_S, and M_r values, along with relatively higher H_C. These characteristics align with some of the essential criteria for effective microwave absorber materials, which include high saturation magnetization and low coercivity [4,5]. Recent research has also highlighted the potential of ferrite-based materials, particularly those doped with rare-earth elements such as Y, for use in electromagnetic applications [26].

In addition to cation substitution, other parameters that significantly affect the structure and magnetic properties of materials include composition, synthesis method, and heat treatment conditions [3,27-30]. This has been confirmed by several previous studies. Sarker et al. [2] reported the influence of different heating temperatures on BaFe_12−xY_xO₁₉ compounds with x = 0.0, 0.2, 0.4, and 0.6 synthesized by a specific method. They found that increasing the heating temperature tended to enhance the values of M_max, Ms, Mr, and Hc. These changes were also related to variations in crystallite size and structural parameters. Rehman et al. [24] investigated BaFe_12−xY_xO₁₉ compounds (x = 0.0, 0.02, 0.05, 0.08, 0.10 and 0.13) prepared via the solid-state reaction method. Their results showed that the highest M_S value reached 57.135 emu/g, while the lowest H_C was around 2,165.83 Oe under an applied magnetic field of 1 T. On the other hand, Sharma et al. [25] studied BaFe_12−xY_xO₁₉ (x = 0.0, 0.1 and 0.2) synthesized through the co-precipitation method, in which they observed variations in magnetic properties. The highest M_S obtained was 59.85 emu/g, and the lowest Hc was 310 Oe. However, the co-precipitation method tended to reduce M_S and increase H_C when Y was used to substitute Fe in the BaFe_12−xY_xO₁₉ compounds. Therefore, controlling parameters such as cation substitution, synthesis technique, and thermal treatment is crucial for optimizing the magnetic and electronic properties of hexaferrite materials. A deeper understanding of the interactions among these parameters may open new opportunities for more efficient applications.

Although numerous studies have investigated the substitution of Fe with Y in BaFe_12−xY_xO₁₉, there is still limited information regarding the effects of using High Energy Milling (HEM) in the synthesis of this material. HEM was chosen due to several advantages, including its simplicity, low cost, the production of more homogeneous particle sizes, and the avoidance of excessive chemical solvents, which results in minimal waste. Therefore, this study investigates the influence of Y substitution on the structural and magnetic properties of BaFe_12−xY_xO₁₉ compounds (x = 0.0, 0.05, 0.1 and 0.15) synthesized using the HEM method. It is expected that HEM may contribute to intrinsic defects and structural modifications that enhance magnetic performance. The aim is to increase the values of M_max, M_S, and M_r, while decreasing H_C, as these parameters are crucial for improving the performance of microwave absorber materials.

Materials and methods

M-type barium hexaferrite compounds with the formula BaFe_12−xY_xO₁₉ (x = 0.00, 0.05, 0.1 and 0.15) were synthesized using the HEM method. To produce the samples, analytical grade precursors were used, including barium carbonate (BaCO₃), iron (III) oxide (Fe₂O₃), and yttrium oxide (Y₂O₃). Sample codes were assigned to simplify identification: Y0 (BaFe₁₂O₁₉), Y5 (BaFe_11.95Y_0.05O₁₉), Y10 (BaFe_11.9Y_0.1O₁₉), and Y15 (BaFe_11.85Y_0.15O₁₉). Before starting the synthesis, the precursors were calculated and weighed based on the designed stoichiometry. All weighed precursors were placed in a milling container, and a small amount of ethanol was added. The milling process was carried out for 3 h at room temperature. The resulting wet powder was dried in an oven at 80 °C for 20 h. Then, the dry powder was sintered at 1,200 °C for 3 h. Finally, the sintered powder was ground manually and sieved to a particle size of 200 mesh, making it ready for characterization.

Structural analysis was carried out using X-ray Diffraction (XRD, SMARTLAB Rigaku) with a Cu-Kα radiation source (λ = 1.54056 Å) over a 2θ range of 10° to 90°, with a step width of 0.01°. Furthermore, the XRD measurements were conducted at room temperature using powder samples. The sample morphology was examined using a Scanning Electron Microscope (SEM), while the elemental distribution was analyzed using Energy Dispersive X-ray Spectroscopy (EDX). Both characterizations were performed with a HITACHI-SU3500 SEM-EDX instrument operated at 15 kV. The magnetic properties of the materials were characterized at room temperature using a Vibrating Sample Magnetometer (VSM250, Dexing Magnet Ltd) under an applied magnetic field range of 0 - 1 T.

Results and discussion

The structural properties

Figure 1 presents the XRD patterns of BaFe_12−xY_xO₁₉ compounds with x = 0.0, 0.05, 0.1, and 0.15 (M-type hexaferrite, BaM), measured over a 2θ range of 10° - 90°. The measurements were conducted at room temperature using powder samples. Several prominent diffraction peaks indicating the presence of the BaFe_12−xY_xO₁₉ phase were observed, appearing at approximately the following 2θ positions: 23.0° (006), 30.3° (110), 30.8° (112), 31.2° (008), 32.1° (107), 34.1° (114), 35.1° (200), 37.1° (203), 40.3° (205), 42.7° (206), 46.5° (10 11), 50.3° (209), 55.3° (217), 57.3° (304), 63.5° (224), 67.3° (20 14), 71.8° (11 16), and 74.1° (403) [2,29]. Furthermore, the inset in Figure 1 shows a leftward shift of the diffraction peaks with increasing Y concentration, suggesting changes in the structural parameters of the compound. Structural analysis (including crystal structure, lattice parameters, average crystallite size, and theoretical density) was carried out using the Rietveld refinement method with the aid of FullProf software [20,25].

The results of the Rietveld refinement analysis confirmed that all compounds exhibit XRD patterns consistent with the ICSD-16157 reference. Figure 2 presents all the graphs obtained from the observed Rietveld refinement analysis. All detected peaks validate the formation of a single-phase BaM with a hexagonal crystal structure belonging to the space group P63/mmc [31,32]. In detail, the structural parameters obtained from the Rietveld refinement analysis are summarized in Table 1. The lattice parameters indicate that the values of a, b, c, and the lattice volume tend to increase slightly with the substitution of Fe³⁺ ions by Y³⁺ ions. This can be explained by the fact that the ionic radius of Y³⁺ (1.04 Å) is larger than that of Fe³⁺ (0.64 Å), causing a mismatch in the crystal lattice when Y³⁺ ions substitute Fe³⁺ ions, which in turn increases the lattice parameters [2,25,33,34]. In addition, the type of BaM formed can be determined by comparing the lattice parameter ratio c/a within a specific range. Sarker reported that BaFe_12−xY_xO₁₉ (x = 0.0, 0.2, 0.4 and 0.6) has c/a values in the range of 3.93 - 3.94 [2]. Wagner reported that M-type BaGa₁₂O₁₉ has a c/a ratio of 3.96 [35]. Topkaya also reported that BaFe_11.9Y_0.1O₁₉ has a c/a ratio of 3.936 [9]. Furthermore, Ginting reported that BaFe_11.8Co_0.1Ni_0.1O₁₉ has a c/a ratio of 3.95 [6], while Ba_0.8Ca_0.2Fe₁₂O₁₉ has a c/a ratio of 3.92 [36]. For a more complex doping system, BaCo₁Zr₁Fe₁₀O₁₉ exhibits a c/a ratio as high as 3.97 [52]. Based on these reports, it can be concluded that M-type barium hexaferrites typically exhibit c/a ratios in the range of 3.92 - 3.97. Therefore, the synthesized BaFe_12−xY_xO₁₉ compounds with x = 0.0, 0.05, 0.1, and 0.15 can be classified as M-type barium hexaferrites. As a schematic illustration, the hexagonal crystal structures of the M-type compounds are shown in Figure 3.

Figure 1 XRD patterns of BaFe_12−xY_xO₁₉ compounds with x = 0.0, 0.05, 0.1 and 0.15 in the 2θ range of 10° - 90°, with an inset showing the XRD patterns in the 2θ range of 30° - 35°.

Figure 2 XRD patterns resulting from the Rietveld refinement analysis for BaFe_12−xY_xO₁₉ compounds with x = 0.0, 0.05, 0.1, and 0.15, where the black circles represent the experimentally observed XRD data (I_Obs), the red line corresponds to the calculated XRD pattern obtained from the Rietveld refinement (I_Calc) that matches the experimental data, the blue line indicates the difference between the observed and calculated patterns, and the green vertical lines mark the Bragg reflection positions.

Table 1 Structural parameters obtained from the XRD pattern analysis of BaFe_12−xY_xO₁₉ compounds with x = 0.0, 0.05, 0.1, and 0.15.

Figure 3 Schematic illustration of the hexagonal crystal structure obtained from the Rietveld refinement of BaFe_12−xY_xO₁₉ compounds for (a) x = 0.0, (b) x = 0.05, (c) x = 0.1, and (d) x = 0.15.

The average crystallite size was determined using the Debye-Scherrer equation, which is defined as follows [2,20]:

where, D_SC is the average crystallite size, k is the Scherrer constant, λ is the X-ray wavelength, β is the full width at half maximum (FWHM), and θ is the Bragg diffraction angle. The calculated Dsc values, as presented in Table 1, show a decreasing trend with increasing substitution concentration of Y ions. The D_SC values were found to be in the range of 76.07 - 87.09 nm. This reduction is consistent with the report by Almessiere, which demonstrated that the substitution of Fe with Nb in BaFe_12−xNb_xO₁₉ led to a decrease in average crystallite size from 46.1 nm (x = 0) to 33.2 nm (x = 0.1) [37]. This phenomenon is associated with the leftward shift of XRD peaks due to Y ion substitution, as shown in the inset of Figure 1. This statement is supported by the report of Marouani, who stated that the leftward shift of XRD peaks may contribute to a reduction in Dsc values [38]. This peak shift is attributed to the larger ionic radius of Y³⁺ compared to Fe²⁺, which can cause significant changes in various structural parameters. These changes include: (i) a decrease in Fe-O bond length, (ii) alterations in the Fe-O-Fe bond angle and position, and (iii) modifications in the overall dimensions of the crystal unit cell, all of which affect the fundamental properties of the structure [20,38]. These structural changes have a direct impact on the fundamental characteristics of the compound. Furthermore, the crystallite size can be used to calculate the dislocation density (σ) through the relationship σ = 1/D_SC². The observed significant reduction in crystallite size likely corresponds to an enhancement in dislocation density within the material [20]. Therefore, the leftward shift in XRD peaks observed in these samples can be well explained by the influence of cation substitution on the structural parameters.

The density of all samples was calculated using data obtained from the Rietveld refinement of X-ray diffraction patterns, according to the following equation [39-41]:

where represents the density determined from XRD measurements (g/cm³), Z is the number of molecules per unit cell, M is the molecular weight (g/mol), N is Avogadro’s constant (6.021×10²³ mol⁻¹), and V is the unit cell volume. The analysis results show that the XRD density values tend to remain stable without significant changes, even though the molar mass of Y³⁺ ions (88.908 a.m.u) is higher than that of Fe³⁺ ions (55.85 a.m.u) [2]. This is due to the very small amount of Fe cation substitution by Y. When compared to the theoretical density of Ba_0.5Sr_0.5RE_0.6Fe_11.4O₁₉ compounds (RE = La, Yb, Sm, Gd, Er, Eu and Dy), the density of BaFe_11.9Y_0.1O₁₉ was found to be higher than that of Ba_0.5Sr_0.5Yb_0.6Fe_11.4O₁₉ ( = 5.291 g/cm³). However, for RE substitutions other than Yb, the values of Ba_0.5Sr_0.5RE_0.6Fe_11.4O₁₉ were higher than that of BaFe_11.9Y_0.1O₁₉, indicating that the Ba_0.5Sr_0.5RE_0.6Fe_11.4O₁₉ compounds are denser. Additionally, the variation in values correlates with the dislocation density values observed, where no significant change in dislocation density was noted. This phenomenon is consistent with the substitution of Fe by Y in BaFe_12−xY_xO₁₉ compounds (with x = 0.0, 0.3, 0.5, 0.7 and 0.9), where increasing x leads to an increase in dislocation density, which in turn decreases the XRD density [20].

The morphological properties

The SEM images of BaFe_12−xY_xO₁₉ compounds with x = 0.00, 0.05, 0.10, and 0.15 are shown in Figure 4. The surface morphology exhibits irregular grain shapes and sizes. This is clearly evident from the presence of both large and small grains on the surface [42]. The average grain size (D_SEM) of each sample was calculated using the ImageJ software. The obtained D_SEM values show a decreasing trend with increasing Y concentration. The D_SEM values are 813, 791, 620 and 519 nm for Y0, Y5, Y10, and Y15 samples, respectively. More detailed results of the D_SEM values can be seen in the histogram shown in Figure 4 and in Table 1. The decrease in D_SEM is presumably due to the cation substitution effect by rare-earth ions such as Y³⁺, which have a different average ionic radius compared to Fe³⁺ ions [37,43]. On the other hand, the presence of Y³⁺ ions, as a rare-earth element, may contribute to the inhibition of grain growth during the heating process [23].

In addition, this study used only 1 synthesis batch for each sample composition. The relatively large standard deviations in grain size values, as shown in Table 1, may be caused by variations during the milling and sintering steps. Although the overall trend of decreasing grain size with higher Y content is still clear, the consistency of the High Energy Milling (HEM) method has not been fully evaluated. Future studies are needed to repeat the synthesis process using multiple batches in order to check reproducibility and improve control over particle size. This would help ensure that the relationship between microstructure and magnetic properties is more reliable.

Table 2 The semi-quantitative results from the EDX measurements compared with the stoichiometry.

Figure 4 The grain size distribution histogram and inserted SEM micrographs BaFe_12−xY_xO₁₉ (a) x = 0.0, (b) x = 0.05, (c) x = 0.1, and (d) x = 0.15 compounds.

Figure 5 The EDX measurement results in the form of spectral curves and elemental mapping of the BaFe_12−xY_xO₁₉ (a) x = 0.0, (b) x = 0.05, (c) x = 0.10, and (d) x = 0.15 compound.

Figure 5 presents the spectrum and elemental mapping results from the EDX measurements for all samples. The spectral curves confirm that the detected elements for the Y0 sample are Ba, Fe, and O, while for the Y5, Y10, and Y15 samples, the detected elements are Ba, Fe, Y, and O. This confirms that the detected elements are consistent with the intended compound [20]. To further validate the synthesized compounds, the atomic percentages of each element in BaFe_12−xY_xO₁₉ (x = 0.00, 0.05, 0.10 and 0.15) were compared with the theoretical stoichiometry, as tabulated in Table 2. The comparison results further confirm that each synthesized compound was successfully produced in accordance with its stoichiometry.

Magnetic properties

The magnetic properties of the BaFe_12−xY_xO₁₉ compounds (x = 0.0, 0.05, 0.10 and 0.15) were measured using a VSM instrument at room temperature under an applied magnetic field of 10 kOe, as shown in Figure 6. The magnetic behavior exhibited is characteristic of hard magnetic materials, indicated by high coercivity and remanent magnetization values, which are typical features of M-type hexaferrites [44-49]. The magnetization of BaFe_12−xY_xO₁₉ (x = 0.0, 0.05, 0.10 and 0.15) correlates with the aligned magnetic field, influencing an increase in magnetization values [24]. Based on Figure 6, the identifiable magnetic parameters include M_max, H_C and M_r. More detailed information regarding these parameters is summarized in Table 3. The observed maximum magnetization values were 50.39, 53.23, 49.65, and 47.95 emu/g for Y0 to Y15, respectively. Furthermore, a similar pattern was observed in the remanent magnetization values, which increased upon partial substitution of Fe³⁺ with Y³⁺ ions. The remanent magnetization values were 32.75, 34.06, 31.53, and 30.51 emu/g for Y0 to Y15, in sequence. The trend of increasing followed by decreasing magnetization values may be attributed to high-temperature sintering (> 1,000 °C) and structural distortion caused by cation substitution of Fe³⁺ with Y³⁺ [2,20]. Mechanistically, each Fe³⁺ ion in a single unit cell of M-type hexaferrites occupies 5 crystallographic sites, including 1 trigonal bipyramidal site (2b), 1 tetrahedral site (4f1), and 3 octahedral sites (2a, 12k and 4f₂) [11]. Moreover, it is known that 16 Fe³⁺ ions have spins aligned parallel to the c-axis of the crystal (forming the majority spin direction ↑ at sites 12k, 2a and 2b), while 8 Fe³⁺ ions are oriented in the opposite direction (forming the minority spin direction ↓ at sites 4f₁ and 4f₂) [19,50]. After the cancellation of the opposing magnetic moments between upward and downward spins of Fe³⁺ ions, a net magnetization results from 4 Fe³⁺ ions with upward spins. Therefore, it is understood that the substitution of Fe³⁺ with Y³⁺ ions at x = 0.05 tends to occupy the minority spin sites ↓ (4f₁ and 4f₂), resulting in an increase in the M_max value in the Y5 sample [50,51]. On the other hand, in the Y10 and Y15 samples, it is suspected that some Fe³⁺ ions are removed from the majority spin sites, leading to a reduction in both maximum and remanent magnetization values [2,9,52].

The M-H loop curves of the Y0-Y15 samples measured under a maximum magnetic field of 10 kOe do not exhibit saturation. To gain a more detailed understanding of the magnetic properties, such as saturation magnetization, effective magnetocrystalline anisotropy constant and anisotropy field, these parameters can be calculated using the Law of Approach to Saturation (LAS) method. The LAS approach is defined as follows [33,53]:

where M_S is the saturation magnetization, A is a constant associated with material inhomogeneities, B is a constant related to magnetocrystalline anisotropy, H is the applied magnetic field, and χ is the magnetic susceptibility of the material. It is known that the χH term is considered significant only at high temperatures and high magnetic fields. Therefore, for samples measured at room temperature, this term can be neglected due to its negligible effect. As a result, Eq. (3) is simplified to Eq. (6). Furthermore, the estimation of the magnetic moment of the BaFe_12−xY_xO₁₉ compounds can be obtained using Eq. (7), where M_W represents the molecular weight [2,53].

Figure 6 M-H loop curves of BaFe_12−xY_xO₁₉ compounds (x = 0.0, 0.05, 0.10 and 0.15) measured at room temperature. The magnetization peaks for all samples are magnified in the inset.

The LAS method approach was applied to the M-H loops of all samples, as shown in Figure 7. Based on the fitted curves in the figure, several magnetic parameters were obtained, including saturation magnetization, effective magnetocrystalline anisotropy constant ( ) , anisotropy field ( ), and magnetic moment ( ), which are summarized in Table 4 and compared with previous studies. Variations in the and values were observed as the substitution of Fe³⁺ cations with Y³⁺ ions increased, showing a general decreasing trend. A high value indicates that the material exhibits hard magnetic characteristics, while a low value suggests soft magnetic behavior [53]. The effective anisotropy constant is influenced by particle size effects on the surface and size limitations. As the particle size decreases, the surface to volume ratio increases, leading to a greater contribution from surface anisotropy. This anisotropy arises due to the different bonding environments experienced by atoms at the surface compared to those in the bulk of the material. As a result, smaller particles tend to exhibit higher values. Conversely, in larger particles, is more strongly affected by the intrinsic properties of the material and its crystal structure [53]. Meanwhile, the obtained values tend to decrease with increasing substitution of Fe³⁺ by Y³⁺, which may be associated with the reduction in magnetocrystalline anisotropy of the material [42]. Furthermore, the magnetic moment values remained relatively stable, as summarized in Table 4

Figure 7 Plot of magnetization as a function of 1/ for BaFe_12−xY_xO₁₉ (a) x = 0.0, (b) x = 0.05, (c) x = 0.1, and (d) x = 0.15 compounds.

Based on Table 3, the optimal BaFe_12−xY_xO₁₉ composition for microwave absorber applications should exhibit low coercivity and high saturation magnetization. These characteristics are crucial because low coercivity allows the material to respond easily to an external magnetic field, while high saturation magnetization enhances the efficiency of electromagnetic wave absorption. In this study, the sample with x = 0.05 (Y5) demonstrated the best combination of these 2 parameters, making it a superior candidate compared to the other samples. Compared to previous studies, the Y5 sample exhibited competitive magnetic properties. Sarker et al. [2] synthesized BaFe_11.8Y_0.2O₁₉ via the sol-gel method and reported a high saturation magnetization (Ms) of 106.0 emu/g and coercivity (Hc) of 2389 Oe. Using the co-precipitation method, Ginting et al. [6] obtained Ms = 34.83 emu/g and Hc = 2099 Oe for BaFe₈Co₂Ni₂O₁₉. Meanwhile, Rehman et al. [24], through a solid-state reaction method, achieved Ms = 57.14 emu/g and Hc = 2,165 Oe for Ba_1−xY_xFe₁₂O₁₉ with x = 0.05. In comparison, the Y5 sample in this study, synthesized using High Energy Milling, achieved Ms = 58.11 emu/g and Hc = 2,715 Oe.

Although the coercivity was slightly higher than that reported in Rehman et al. [24], the Y5 sample offers a favorable trade-off between magnetization strength and coercive field, which is critical for microwave absorption performance. This result highlights the potential advantage of the HEM technique in producing materials with improved microstructural uniformity and magnetic homogeneity. Accordingly, the BaFe_11.95Y_0.05O₁₉ composition can be considered a promising candidate for high-performance microwave absorbing materials

Table 3 Magnetic variables of BaFe_12−xY_xO₁₉ (x = 0.0, 0.05, 0.1 and 0.15).

Table 4 Magnetic variables of BaFe_12−xY_xO₁₉ (x = 0.0, 0.05, 0.1 and 0.15) approaching by LAS method.

Conclusions

The results of this study indicate that the addition of Yttrium (Y) as a dopant in barium hexaferrite (BaFe_12−xY_xO₁₉) significantly affects the microstructure and magnetic properties of the material. The incorporation of Y leads to an increase in lattice parameters, shifts in XRD diffraction peaks, and a reduction in grain size, which in turn impacts the magnetic characteristics. Magnetic measurements reveal that the sample with x = 0.05 (Y5) exhibits the best performance, with the highest saturation magnetization (58.11 emu/g) and optimal coercive field (2,715 Oe). Therefore, Yttrium doping has proven effective in enhancing the magnetic properties of this material, making it a promising candidate for microwave absorber applications and other electromagnetic technologies.

Acknowledgements

The author would like to express sincere gratitude to the Graduate School of Universitas Sumatera Utara (USU), Indonesia for the support and facilities provided throughout the research process. Special thanks are also extended to the Research Center for Advanced Physics and Materials (PRMM) - BRIN for the technical assistance, laboratory facilities, and valuable scientific guidance during the implementation of this research.

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During the preparation of this work the authors used ChatGPT-4.0 in order to improving clarity and language quality. All scientific content, interpretation, and conclusions were developed independently by the authors. After using this tool/service, the authors reviewed and edited the content as needed and takes full responsibility for the content of the publication.

CRediT author statement

Nazaruddin Nasution: Conceptualization, Writing - original draft, Writing - review & editing, Investigation, Formal analysis. Syahrul Humaidi: Writing - review & editing, Formal analysis, Supervision. Erna Frida: Writing - review & editing, Investigation. Marzuki Naibaho: Writing - review & editing, Methodology, Resources, Data curation, Investigation, Formal analysis. Phahul Zhemas Zul Nehan: Writing - review & editing, Software, Investigation, Formal analysis, and Data Curation. Masno Ginting: Writing - review & editing, Formal Analysis, Validation, Supervision. Tulus Na Duma: Writing - review & editing, Investigation.

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