Trends Sci. 2026; 23(4): 11410

Introduction

The study of material modification has a long-standing history and continues to evolve toward developing ideal materials for specific applications. Notably, the investigation of doped perovskite manganites (RE_1−xA_xMnO₃, where RE represents rare earth elements and A denotes alkaline and alkaline earth metals) has been significantly investigated [1,2]. This interest is due to the intriguing magnetic properties of

doped perovskite manganites, including colossal magnetoresistance, the magnetocaloric effect, multiferroic, magnetostriction, and microwave absorption [3,4]. The emergence of these magnetic phenomena in perovskite manganites is closely linked to the exchange interactions involving Mn ions. In the case of doped lanthanum manganite, the introduction of divalent ions such as Ca²⁺ and Sr²⁺ leads to the formation of mixed-valence Mn ions, specifically Mn³⁺ and Mn⁴⁺. The presence of Mn⁴⁺ facilitates double-exchange interactions in the Mn³⁺-O²⁻-Mn⁴⁺, which partially supplants the super-exchange interactions within the Mn³⁺-O²⁻-Mn³⁺. These interactions play a crucial role in altering the material’s magnetic behavior from antiferromagnetic to ferromagnetic [3]. Therefore, the magnetic properties of lanthanum manganite (LaMnO₃) present considerable promise for diverse applications, such as magnetic refrigeration technology, sensors, spintronics, magnetic random access memory (MRAM), and cancer treatment via hyperthermia methods [3,5,6].

Magnetic properties are known to be highly sensitive to various structural parameters through material modification aimed at obtaining superior materials. The fundamental aspect of material adjustment involves heat treatment, synthesis methods, and material composition [3,7-9]. For instance, Ezaami et al. [10] conducted a comparison of synthesis methods between solid-state and sol-gel for La_0.7Ca_0.2Sr_0.1MnO₃ samples. They revealed that differences in synthesis methods affect structural parameters such as lattice parameters, unit cell volume, crystallite size, and grain size. The solid-state method exhibited larger grain sizes compared to the sol-gel method. In other examples, Pan et al. [11]; Mahjoub et al. [12] also compared synthesis methods between solid-state and sol-gel. They revealed that the lattice parameters and average grain size of the solid-state method were larger than sol-gel method. Additionally, several other studies comparing the effects of solid-state and sol-gel synthesis methods confirm that variations in structural parameters, primarily crystallite size, grain size, and grain distribution homogeneity, significantly contribute to the magnetic properties of the materials [13,14]. Furthermore, Munazat et al. [15] reported a comparison of synthesis methods for La_0.7Ba_0.1Ca_0.1Sr_0.1MnO₃ between sol-gel and wet-mixing methods. They noted that differences in synthesis methods influence crystallite and grain sizes, with the sol-gel samples demonstrating greater magnetization than those produced via wet-mixing, attributed to the larger grain size of the sol-gel samples. The structural parameter differences between sol-gel and wet-mixing methods arise from internal stress or defects in the structure, along with variations in mechanical and chemical treatments.

Each synthesis method has advantages and disadvantages. The solid-state method is suitable for producing ceramics with larger particle sizes, but it has weaknesses such as producing inhomogeneous particles, requiring long holding times, and high sintering temperatures for heat treatment [3,9,16]. Consequently, many researchers have alternative synthesis methods as the sol-gel method. This method can produce more uniform particle sizes. Additionally, the sol-gel method offers several advantages, including an easier production process, lower sintering temperatures, and shorter holding times than the solid-state method [10-12]. On the other hand, the wet-mixing method has not been extensively explored. However, previous studies have reported that it provides higher efficiency than the sol-gel method. This is because the wet-mixing method does not require additional precursors (such as citric acid as a metal complexing agent and ethylene glycol as a polymerization agent) and experiences less mass loss due to the absence of a combustion process [9,15,17]. Therefore, the choice of synthesis method remains a critical consideration for compound production.

The La_0.7Ca_0.2Sr_0.1MnO₃ compound has been extensively studied due to its attractive magnetic properties, such as a Curie temperature around room temperature, magnetocaloric effect, and colossal magnetoresistance phenomenon [10,18,19]. However, studies on compounds with the addition of small vacancies (□) at the A-site, specifically for the La_0.7Ca_0.2Sr_0.1MnO_3, are still limited. The presence of vacancies is expected to affect the structural and magnetic properties of the compound. For example, Chakroun et al. [20] reported that a small number of vacancies at the Ca²⁺ ion in La_0.7Ca_0.29□_0.01MnO₃ affects its magnetic properties, as evidenced by a change in magnetization. These are shown by changes in magnetic properties, including magnetization value, magnetic state, and Curie temperature, which often correlate with variations in the Mn³⁺/Mn⁴⁺ ion ratio. In addition, Arun et al. [21] also reported that adding a small number of vacancies in Sr²⁺ ions of La_0.67Sr_0.24□_0.09MnO₃ affects structural and magnetic changes, similar to previous findings. Furthermore, this experiment serves as a continuation of the previous study conducted by Nehan et al. [22], which investigated the structural, magnetic, and magnetocaloric properties of La_0.7Ca_0.2−x□_xSr_0.1MnO₃ compounds synthesized via the solid-state method. It is believed that the change in magnetic properties is driven by structural modification due to material modification. Therefore, further investigation is needed to explore the contribution of small vacancies and variations in synthesis methods such as solid-state reaction, sol-gel, and wet-mixing to the structural and magnetic properties of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds.

Materials and methods

The synthesis of the compound La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ was conducted using several methods, including solid-state reaction, sol-gel, and wet-mixing. Details regarding the precursors used and the steps for each synthesis method are explained in the following sections. To simplify sample identification, terms such as LV-5-SSR, LV-5-SG, and LV-5-WM were adopted to represent samples produced via solid-state reaction, sol-gel, and wet-mixing methods, respectively. After dried samples were obtained from each synthesis process, they were subjected to heat treatment. The dried samples underwent calcination at 600 °C for 6 h, followed by re-grinding and pre-sintering at 900 °C for 12 h. The pre-sintered material was then re-grinded and prepared for pelletization into cylinders with a diameter of 1 cm and a thickness of 2 mm, under a pressure of 10 tons. Finally, the pelletized samples were sintered at 1,200 °C for 24 h to achieve optimal grain growth.

The process of the solid state reaction method

The precursors used to produce La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ are La₂O₃ (Merck), CaCO₃ (Merck), SrCO₃ (Sigma-Aldrich), and MnCO₃ (Sigma-Aldrich), all of high purity. The process begins with weighing all precursors according to stoichiometric calculations, followed by mixing in an agate mortar for 45 min. The well-mixed sample then proceeds to the heat treatment as outlined in the previous section.

The process of the sol-gel method

In the sol-gel method, the precursors used are La₂O₃ (Merck), Ca(NO₃)₂·6H₂O (Merck), Sr(NO₃)₂ (Merck), and Mn(NO₃)₂·4H₂O (Merck), all of high purity. To synthesize La_0.7Ca_0.15□_0.05Sr_0.1MnO₃, each precursor is weighed according to stoichiometric calculations. The process begins with the addition of citric acid (HNO₃) to dissolve La₂O₃, while the other precursors are dissolved in distilled water. All dissolved precursors are mixed in a larger beaker. Citric acid (CA) is then added as a complexing agent, and ethylene glycol (EG) is added as a polymerization agent in a molar ratio of 1:2:4 for total metal:CA:EG, respectively. The mixture is heated to 70 - 80 °C and continuously stirred to accelerate the polyesterification reaction between CA and EG. The solution is then titrated with ammonium hydroxide until a neutral pH of 7 is achieved. The solution is kept warm until it forms a thick gel. The gel is evaporated in an oven at 190 °C overnight until a black powder is obtained. Finally, the powder is ground and prepared for the heat treatments.

The process of the wet-mixing method

In the wet-mixing method, the precursors used include La₂O₃ (Merck), CaCO₃ (Merck), SrCO₃ (Sigma-Aldrich), and MnCO₃ (Sigma-Aldrich), all of high purity. Each precursor is weighed according to stoichiometric calculations. The process begins with dissolving all the precursors and mixing them with a 65% nitric acid (HNO₃) solution as a solvent. The combined precursor solutions are continuously stirred while being heated to 80 °C until the solution evaporates and dries. Subsequently, the resulting powder is placed in an oven at 190 °C to ensure the removal of moisture and HNO₃. Finally, the powder is ground and prepared for the heat treatment process.

Characterizations

The characterizations of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ from the 3 synthesis methods were performed to confirm their structural and magnetic properties. X-ray diffraction (XRD) patterns were obtained using Bragg-Brentano geometry on an X’pert PAN-analytical diffractometer with CuKα radiation (λ = 1.5406 Å) over a 2θ range of 10° - 90°, measured at room temperature. Morphological and elemental analyses were conducted using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) with a Quanta 650 Thermofisher Scientific-SEM and an Xplore 15 Oxford Instruments-EDS system. The functional groups of the materials, particularly of the MnO₆ octahedral structure, were investigated using Fourier Transform Infrared Spectroscopy (FTIR) from Bruker Alpha II, covering a wavenumber range of 500 - 4,000 cm⁻¹. Magnetic properties were studied using a Vibrating Sample Magnetometer (VSM) from the National Research and Innovation Agency of Indonesia, with measurements conducted on powder samples at room temperature and under a magnetic field of 10,000 Oe.

Results and discussion

X-ray diffraction analysis

The XRD patterns of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds measured at room temperature for the variations in synthesis methods: solid-state reaction, sol-gel, and wet-mixing. Figure 1(a) shows sharp peaks with high intensity, which are often associated with a high degree of crystallinity in the sample [22-25]. In addition, Figure 1(b) provides a more detailed view of the (121) crystal plane peak within the 2θ range of 32° - 33.5°, where a shift in the peak occurs at specific diffraction angles. According to Bragg’s relation ( ), this slight peak shift indicates changes in the structural parameters of each sample [26-28]. The structural analysis of the XRD data was performed using the Rietveld refinement method with a pseudo-Voigt function in the FullProf program. All samples have a single-phase characteristic of LaMnO₃ phase corresponding to the orthorhombic crystal structure with the Pnma space group. The Rietveld analysis results are illustrated in Figures 2(a) - 2(c), which compares the intensity of experimental Bragg reflection data between observed (I_Obs) and calculated (I_Calc) results, demonstrating a good fit. The XRD analysis provided several structural parameters, including phase determination, crystal structure, crystallite size, theoretical density, atomic positions, and other parameters, as summarized in Table 1.

Figure 1 Powder X-ray diffraction patterns of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds within the 2θ range (a) 10° - 90° and (b) 32° - 33.5°.

Several prior studies have commonly employed the Goldschmidt tolerance factor (t), as expressed in Eq. (1), to estimate the crystal structure of LaMnO₃ phases [26,29]:

Where <r_A>, <r_B>, and r_O represent the average ionic radii for the A, B, and oxygen sites, respectively.

All average ionic radii values were calculated using Eq. (2), utilizing the ionic radii of each ion based on the standard coordination number of nine at the A-site: La³⁺ (1.22 Å), Ca²⁺ (1.18 Å), Sr²⁺ (1.31 Å), Mn³⁺ (0.65 Å), Mn⁴⁺ (0.53 Å), and O²⁻ (1.38 Å) [30]. The average ionic radii calculations for all parameters are summarized in Table 2. Previous literature indicates that t values have several representations concerning the crystal structure of LaMnO₃ phases. If a value of t equal to 1 is confirmed, the crystal structure of LaMnO₃ is cubic. Additionally, if t falls within the range of 0.96 < t < 1, it indicates the formation of a rhombohedral crystal structure. Conversely, if t < 0.96, it represents an orthorhombic crystal structure [3,31]. The Goldschmidt tolerance factor approximations for all samples are 0.902, which is in line with the criterion of t < 0.96. Therefore, the results confirm that the formed crystal structure is orthorhombic, aligning with the theoretical calculations from the XRD experiments.

Table 1 Structural parameters obtained by Rietveld refinement for powder XRD patterns of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds with various synthesis methods.

Table 2 Goldschmidt tolerance factor calculation for La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds synthesized using solid-state reaction, sol-gel, and wet-mixing.

Based on Table 1, the lattice parameters a, b, and c show different values for each sample, while the unit cell volume tends to be constant. The LV-5-SSR sample exhibits the largest lattice parameter values, which can be attributed to the noticeable leftward shift of the main (121) peak compared to other samples. In contrast, the (121) peak of the LV-5-SG sample appears at the far right [32]. These differences in lattice parameters are clearly reflected in the peak shifts observed in the XRD patterns, as illustrated in Figure 1(b). This is linked to several reasons, including (i) differences in production mechanisms, where solid-state reaction is based on dry reactions, while sol-gel and wet-mixing are based on wet reactions, and (ii) the types of precursor materials used [3,11,12]. Moreover, the dry reaction method is often associated with less uniform atomic-level homogeneity and slower atomic diffusion, which generates microstrain, as shown in Table 1. This, in turn, leads to higher structural defects, resulting in larger lattice parameters compared to wet-chemistry-based synthesis routes [16]. The lattice parameter values of sol-gel and wet mixing are relatively constant, which helps to understand these reasons. For instance, Ezaami et al. who investigated the effects of synthesis methods between solid-state and sol-gel for La_0.7Ca_0.2Sr_0.1MnO₃ [10], and Munazat et al. [15] who examined a study of synthesis comparison between sol-gel and wet-mixing for La_0.7Ba_0.1Ca_0.1Sr_0.1MnO₃ compounds, have also reported lattice parameter differences due to variations in the synthesis methods.

Further analysis indicates that the orthorhombic crystal structure can be categorized into 2 types based on the lattice parameters a, b, and c. If the lattice parameters satisfy the condition and a < c, it indicates O-type orthorhombic distortion. Conversely, if , it suggests O’-type distortion [31]. The O-type distortion arises from the cooperative bending of corner-sharing octahedra, while the O’-type distortion is due to cooperative Jahn-Teller distortions associated with the rotation of MnO₆ octahedra [22,33]. The LV-5-SSR sample satisfies the criteria for exhibiting an orthorhombic O-type distortion, whereas the LV-5-SG and LV-5-WM samples exhibit an O’-type distortion. This distinction is also indicated by the (121) peak, where LV-5-SG and LV-5-WM tend to show an additional peak on the left side. In contrast, the LV-5-SSR sample, characterized by O-type distortion, displays only a single peak without any splitting. This observation is consistent with previous reports by Moreno et al. [18]; Sakka et al. [31]. Figures 2(d) - 2(i) display the relationship between the lattice parameters and the type of orthorhombic distortion in schematic illustrations of the crystal structure and MnO₆ octahedral structure. The presence of MnO₆ octahedral distortion indicates the characteristics of Jahn-Teller distortion in all samples [27,31]. This is strongly supported by variations in the Mn-O bond lengths, including the short Mn₁-O₂, medium Mn₁-O₁, and long Mn₁-O₂ bonds, as well as changes in the Mn₁-O₁-Mn₁ and Mn₁-O₂-Mn₁ bond angles, both of which are influenced by differences in the synthesis process [9,14,17]. The alteration of these parameters collectively indicates the presence of Jahn-Teller distortion within the complex orthorhombic crystal structure. These variations in bond lengths and angles are associated with the impact of electron transfer processes occurring within the system [15]. The crystallite size of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ samples with varying synthesis methods has been estimated using peak diffraction data via the Williamson-Hall equation, as presented below [15,34]:

where, represents the average crystallite size calculated using the Williamson-Hall equation, k is a constant related to the sharpness factor of the crystallite (0.94), λ is the wavelength of the XRD source, β is the full width at half maximum (FWHM) related to the peak intensity of diffraction, θ represents the diffraction angle, and is the strain coefficient [15]. This method is effectively considered as it incorporates strain broadening, reflecting the influence of synthesis processes (such as heat treatment, synthesis procedures, and milling) and defects within the crystallites (including lattice defects, doping-induced defects, and uneven atomic distribution) [34]. The value of D_{W - H} is derived from the intercept of the fitting results, while ε is obtained from the slope of the fitting. The D_{W - H} and ε values are summarized in Table 1. It is noteworthy that differences in synthesis methods significantly affect crystallite size [10,16]. As reported in previous studies, the parameters D_{W - H} and ε exhibit a strong correlation [22]. A high value of ε typically indicates a significant number of defects within the material, leading to the formation of inhomogeneous crystallites and consequently resulting in a smaller D_{W - H} value. Conversely, a lower ε value suggests fewer structural defects, thereby allowing for the growth of larger crystallites and a higher D_{W - H} value [35-37]. This explanation provides a clear understanding of the observed correlation between D_{W - H} and ε in the LV-5-SSR, LV-5-SG, and LV-5-WM samples.

Figure 2 Rietveld refinement analysis results of XRD patterns for samples (a) LV-5-SSR, (b) LV-5-SG, (c) LV-5-WM, schematic illustration of crystal structures of (d) LV-5-SSR, (e) LV-5-SG, (f) LV-5-WM, and octahedral MnO₆ structure with Mn-O-Mn bond angles.

Furthermore, XRD data can be utilized to estimate the theoretical density using the following equation [38]:

Where M is the molecular mass (g/mol), Z is the number of formula units per unit cell, N_a represents Avogadro’s number (6.0210×10²³ mol⁻¹), and V is the unit cell volume obtained from XRD analysis.

The theoretical density values for each sample were 6.122, 6.149, and 6.141 g/cm³ for LV-5-SSR, LV-5-SG, and LV-5-WM, respectively. In comparison, the parent sample La_0.7Ca_0.2Sr_0.1MnO₃ has a theoretical density of approximately 6.22 g/cm³, while densities for samples produced via solid-state and sol-gel synthesis are around 6.20 g/cm³ [7]. In a recent report, Nehan et al. [22] stated that the P_XRD value of the La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compound synthesized via the solid-state reaction method was found to be 6.14 g/cm³, indicating that the results are consistent and reproducible. Additionally, the difference in theoretical density between the parent sample and La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ can be understood as the introduction of vacancies at the Ca²⁺ sites reduces the overall weight of the sample while maintaining a nearly identical unit cell volume.

Figure 3 SEM image at 2,500× enlargement and histogram distribution of average grain size for (a) LV-5-SSR, (b) LV-5-SG, (c) LV-5-WM, and EDS spectra measurement results for (d) LV-5-SSR, (e) LV-5-SG, and (f) LV-5-WM.

Scanning electron microscope-energy dispersive X-ray spectroscopy analysis

Figure 3 presents histograms of the average grain size (D_SEM), and the inserted picture illustrates the surface morphology of all samples at 2,500× enlargement. Notably, the grains and grain boundaries are visible and exhibit irregular polygonal shapes with no evidence of agglomeration. This observation is consistent with previous studies on the preparation of metal oxides using solid-state reaction, sol-gel, and wet-mixing methods [10,15,39]. The D_SEM values for each sample were calculated using Image-J, which was used to calculate the diameter of all grains in the SEM images. The statistical analysis of the D_SEM is indicated by the peak of the blue distribution line.

The calculations of D_SEM values for LV-5-SSR, LV-5-SG, and LV-5-WM compounds are 3.41, 2.06, and 1.29 μm, respectively. These micrometer scale of D_SEM values are affected by the high heating factor during heat treatment (> 1,000 °C), which encourages the growth of larger grains [3,16]. The LV-5-SSR has the largest D_SEM with a non-homogeneous grain size distribution compared to LV-5-SG and LV-5-WM. This is related to the initial precursor being a rough powder, which allows for a slower reaction process, providing time for grain growth during heating. Prolonged exposure to elevated temperatures leads to coarser grains due to enhanced diffusion and particle coalescence. Previous studies have reported that the absence of a melting process with chemical solutions can increase grain size [9,10]. Although both LV-5-SG and LV-5-WM were mixed with specific chemical solutions, they did not have similar D_SEM values owing to different chemical reactions. The differences in D_SEM values between LV-5-SG and LV-5-WM are often correlated to the pH conditions of the synthesis process. The sol-gel method is generally carried out under neutral conditions (pH ≈ 7), which favor more controlled hydrolysis and condensation, resulting in relatively larger particles. In contrast, the wet mixing method is performed under highly acidic conditions (pH ≈ 1), which can inhibit particle growth and promote the formation of finer grains [15,16]. Therefore, it is believed that the pH conditions and the composition of the chemical solutions play an important role in the grain size formation between LV-5-SG and LV-5-WM [15].

An important aspect to consider is the discrepancy between D_{W - H} and D_SEM, which is often observed in polycrystalline materials. These values may converge only when the material is synthesized at the nanoscale [35,37]. In the case of materials with micrometer-scale grain sizes, D_{W - H} and D_SEM typically differ, which aligns with the definition of a grain, consisting of several crystallites with similar orientations [10]. Based on this definition, the number of crystallites within a single grain can be estimated by calculating the ratio D_SEM and D_{W - H}, as presented in Table 1. This discrepancy can also be understood from the perspective of the measurement techniques employed: (i) D_{W - H} is derived from XRD data on powder samples, representing an indirect measurement based on peak broadening analysis, whereas (ii) D_SEM is obtained through direct observation of pelletized samples using SEM measurement, providing a visual representation of the surface morphology [25]. Therefore, these reasons explain why trends between D_{W - H} and D_SEM are not always in alignment [24,29

Table 3 Atomic percent of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds for all synthesis methods from EDS measurement results.

EDS analysis conducted on all samples revealed the presence of La, Ca, Sr, Mn, and O, confirming the consistency of these elements with the employed chemical formula. The spectra of La, Ca, Sr, Mn, and O elements are illustrated in Figures 3(d) - 3(e). Additionally, semi-quantitative calculations of each element measured on the sample surfaces are summarized in Table 3, which compares these results with stoichiometric calculations. These discrepancies of data demonstrate the alignment between the expected and measured compositions, affirming the success of the applied synthesis methods. On the other hand, the La and Ca exhibit higher at % experimental content than stoichiometric. It can be caused by this surface-sensitive technique that can be influenced by local inhomogeneity, surface segregation, and instrumental error. Moreover, the EDS technique is performed for scanning only on the surface area of samples, which does not directly represent bulk site occupancy. The evidence for Ca-site vacancies is derived from bulk-sensitive Rietveld refinement of XRD patterns using the atom formation of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃. It is supported by the presence of the MnO₆ octahedral structure distortion in the systems. Furthermore, the detailed element distributions of compounds are captured in the mapping SEM images, as shown in Figure 4.

Figure 4 Elemental distribution maps, obtained through EDS measurement, for compounds (a) LV-5-SSR, (b) LV-5-SG, and (c) LV-5-WM. These maps illustrate the elemental distribution of Lanthanum (purple), Calcium (green), Strontium (yellow), Manganese (cyan), and Oxygen (red). Such analysis provides valuable insights into the composition and homogeneity of the samples.

Fourier transform infrared spectroscopy analysis

Figure 5 presents the FTIR spectra of the compounds LV-5-SSR, LV-5-SG, and LV-5-WM, measured in the wavenumber range of 500 - 4,000 cm⁻¹ at room temperature. Previous studies have often associated the presence of the MnO₆ octahedral structure in LaMnO₃ with octahedral symmetry, characterized by 2 infrared bands at 400 and 600 cm⁻¹ [10,40,41]. The absorption dips in the band between 513 and 534 cm⁻¹ are linked to the internal bending mode, resulting from changes in the Mn-O-Mn bond angles [41]. Second absorption dips in the wavenumber range of 590 - 591 cm⁻¹ are associated with the asymmetric stretching mode of the Mn-O-Mn and Mn-O bonds, which is characteristic of the MnO₆ octahedron formation in all samples [10,22,40]. The spectra indicate a reduction in peak intensity at different wavenumbers, correlating with variations in Mn-O bond lengths, Mn-O-Mn bond angles, and unit cell volumes derived from XRD analysis [40,41]. Additionally, the FTIR spectra display stretching vibrations of C=O and C-O in the wavenumber range of 990 - 1,132 cm⁻¹, attributed to carbon residues remaining from the combustion during the heating treatment and FTIR preparation for all samples [40,42]. Notably, the LV-5-SG sample exhibits lower peak intensity in the range of 990 - 1,132 cm⁻¹ compared to the other 2 samples, indicating a reduced carbon residue in this sample. Furthermore, the presence of peaks in the range of 2,000.00 - 2,400.00 cm⁻¹ suggests the presence of CO₂, likely due to the natural porosity of the samples [43,44]. The summary of FTIR information is tabulated in Table 4.

Figure 5 FTIR spectra from La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds for all synthesis methods with wavenumber range of 500 - 4,000 cm⁻¹.

Table 4 Peak positions of absorption bands from FTIR measurements of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds in the wavenumber range 4,000 - 500 cm⁻¹.

Magnetic properties of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds

Magnetic properties were investigated by measuring the magnetization of the La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compound under an applied magnetic field of 10,000 Oe at room temperature. Figure 6 presents the magnetization versus magnetic field (M(_μ0H)) curves obtained from VSM measurements. The maximum magnetization values (M_max) at a magnetic field of 1 T for samples LV-5-SSR, LV-5-SG, and LV-5-WM were found to be 29.50, 42.58, and 33.37 emu/g, respectively. The magnetization behavior of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ correlates with the aligned magnetic field, affecting an increase in magnetization values [45]. All samples exhibited ferromagnetic behavior with soft-magnetic characteristics, as the magnetic properties of LaMnO₃ [15,46]. This is indicated by the coercivity (H_c) and remanence (M_r) values summarized in Table 5. Notably, the magnetization of sample LV-5-SG was higher than that of LV-5-SSR and LV-5-WM. Previous studies have reported several critical parameters influencing the reduction in magnetization, including (i) grain size, (ii) crystallite size, (iii) structural defects, (iv) weakening of ferromagnetic states (due to the Mn³⁺-O²⁻-Mn⁴⁺, double-exchange interaction), and the presence of antiferromagnetic states (from the Mn³⁺-O²⁻-Mn³⁺, super-exchange interaction) resulting from the Mn³⁺/Mn⁴⁺ ratio influenced by the synthesis process, and (v) inhomogeneity in grain and crystallite size distribution [3,13,47]. Yadav et al. [47] noted that an increase in grain size in samples can reduce the non-magnetic layers, contributing to an increase in magnetization, and vice versa. However, structural defects and inhomogeneity in grain size distribution are characteristic of the solid-state reaction method, where the slow grain growth process leads to inhomogeneity and structural defects, thereby reducing magnetization [10,16]. Additionally, this argument is supported by the highest ε values for LV-5-SSR, which may indicate massive defects in the compounds. In contrast, the LV-5-SG and LV-5-WM samples exhibited a more homogeneous grain size distribution and relatively low ε values, reducing defects due to the use of acid-based chemical solutions [35,37]. The homogeneity of grain size distribution for each sample is illustrated in the SEM images shown in Figures 3(a) - 3(c). It is important to note that differences in synthesis methods can contribute to changes in magnetic properties associated with variations in structural parameters.

As shown in Figure 6, all samples measured under a magnetic field of 10,000 Oe do not exhibit saturation magnetization. Several studies reported that the saturation magnetization will be captured in a very high magnetic field [45,48]. Although saturation magnetization values are not known from the experimental data, we can gain detailed information about the magnetic properties (including saturation magnetization (M_S), effective magnetocrystalline anisotropy constant (K_eff), and anisotropy field (H_a) utilizing the Law of Approach to Saturation (LAS) method. The equation of LAS method can be written as follows [49,50]:

In this context, A is a constant reflecting inhomogeneity parameter, B corresponds to the anisotropy factor, μ₀H is the applied magnetic field, and χ represents the magnetic susceptibility. Furthermore, determines the inhomogeneity of materials, refers to against the magneto-crystalline anisotropy, and χμ₀​H is known as a paramagnetism-like term [51]. It is generally accepted that the χμ₀​H term becomes relevant only under high-temperature conditions and vanishes in high-field conditions [50,52]. Consequently, for measurements conducted at room temperature, this term can be omitted due to its minimal contribution. Thus, in these calculations, consider not using χμ₀​H parameter.

Figure 7 exhibits the fitting results of the M(μ₀​H) curves based on the LAS method within the magnetic field range of 4,000 - 1,0000 Oe for all compounds. The calculated values of K_eff and H_a show different values, indicating that the synthesis method strongly influences the magnetic properties of the compounds. It is observed that the trend of all parameters obtained from the LAS fitting is consistent with the experimental magnetic properties. This is in agreement with the reported research by Jithin et al. [53] on La_1−xCa_xMnO₃ compounds, where a higher K_eff typically results in a reduced calculated saturation magnetization M_s. The variation in K_eff among samples is primarily attributed to differences in structural parameters. In this context, grain size and crystallite size play a critical role in determining the magnitude of K_eff. As grain and crystallite sizes decrease, accompanied by an increase in material defects, the surface-to-volume ratio becomes larger, enhancing the contribution of surface anisotropy. This anisotropy arises due to atoms at the surface experiencing a different bonding environment compared to those within the bulk. Consequently, smaller grains and crystallites with high defect concentrations tend to exhibit higher K_eff values. In contrast, larger particles are more influenced by the intrinsic properties of the material and its crystal structure [54]. A similar trend is observed for the H_a parameter, as it is directly correlated with K_eff. A comprehensive summary of the magnetic parameters obtained from the LAS method is provided in Table 5.

Figure 6 Magnetization versus magnetic field curves via VSM measurements of La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds for all synthesis method variations.

Figure 7 Magnetization versus magnetic field curves of samples (a) LV-5-SSR, (b) LV-5-SG, and (c) LV-5-WM with the magnetic field range of 400 - 10,000 Oe, fitted using the Law of Approach to Saturation method.

Table 4 Magnetic parameters of the La_0.7Ca_0.15□_0.05Sr0_.1MnO₃ compounds compared with previous reports.

(*) Note: SSR = solid-state reaction, SG = sol-gel, HEBM = high energy ball milling.

Therefore, it can be understood that differences in processing, particularly the synthesis method, have a significant impact on both the structural parameters and the magnetic properties of the compounds. Additionally, the introduction of a slight calcium deficiency in La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds offers a new perspective on compound formation, which is predicted to enhance the magnetic properties, consistent with several previous reports [20,22,57]. It is expected that the findings of this study can serve as a valuable reference and a potential candidate for the future development of magnetic-based applications, such as active magnetic refrigeration, magnetic sensors, MRAM, and related technologies [3].

Table 5 Magnetic parameters of the La_0.7Ca_0.15□_0.05Sr0_.1MnO₃ compounds approached by the LAS method.

Conclusions

In this summary, La_0.7Ca_0.15□_0.05Sr_0.1MnO₃ compounds were successfully synthesized via solid-state reaction, sol-gel, and wet-mixing methods. All samples have a single-phase orthorhombic crystal structure with Pnma space group. The XRD patterns exhibited sharp peaks with high intensity, indicating good crystallinity. The average crystallite sizes of the samples were 75.79, 113.98, and 107.23 nm, while the average grain sizes were 3.41, 2.06, and 1.29 μm for LV-5-SSR, LV-5-SG, and LV-5-WM, respectively. The difference between these crystallite and grain sizes is connected to the diverse observations, in which crystallite size is calculated using indirect XRD measurement, and grain size is calculated using direct SEM measurement. The Mn-O stretching and Mn-O-Mn bending vibrations, confirmed by FTIR peaks at 513 - 534 and 590 - 591 cm⁻¹, verified the preservation of the MnO₆ octahedral structure in the samples. The investigation of magnetic properties revealed ferromagnetic behavior with soft magnetic type (low coercivity), characterized by high magnetization values of 29.50, 42.58, and 33.37 emu/g for LV-5-SSR, LV-5-SG, and LV-5-WM, respectively. The calculation of saturation magnetization approximately uses LAS methods with the values of 37.11, 46.49, and 40.09 emu/g for LV-5-SSR, LV-5-SG, and LV-5-WM, respectively. LV-5-SG revealed the highest maximum magnetization at room temperature under a 1 T magnetic field. These magnetic properties correlated with large crystallite size, low defect, and the possible Jahn-Teller distortion via the MnO₆ octahedral structure. The observed relationship between synthesis routes and slight calcium ion deficiency-dependent structural parameters (lattice parameters, crystallite size, Mn-O length, and Mn-O-Mn angle bond characteristics) and magnetic properties underscores the strong double exchange-interaction in this system for producing ferromagnetic behavior. These results demonstrate that both synthesis method and Ca ion deficiency can be used as effective tools to tailor structural and magnetic behavior in perovskite manganites. Therefore, this study offers a new perspective on the impact of synthesis methods and calcium ion deficiency in perovskite manganite materials for future applications such as magnetic refrigeration, MRAM, and spintronics.

Acknowledgements

The authors gratefully acknowledged the PMDSU Scholarship for Phahul Zhemas Zul Nehan, and this study was supported by the Faculty of Mathematics and Natural Sciences, Universitas Indonesia, under research grant Hibah Publikasi Pascasarjana FMIPA UI 2024 with contract number PKS-045/UN2.F3.D/PPM.00.02/2024.

Declaration of Generative AI in Scientific Writing

During the preparation of this manuscript paper, the author used Grammarly to improve the manuscript’s readability and language. After using this tool, the author reviewed and edited all content as needed and took full responsibility for the content of the publication.

CRediT Author Statement

Phahul Zhemas Zul Nehan: Conceptualization; Writing - original draft; Writing - review & editing; Investigation; Formal analysis; Software and Visualization. Marzuki Naibaho: Resources and Investigation. Yeni Febrianti: Investigation. Januar Widakdo: Writing - review & editing; Validation and Data Curation. Maykel Manawan: Supervision; Software; Validation and Writing - Review & Editing. Darminto Darminto: Writing - Reviewing and Editing; Supervision and Validation. Budhy Kurniawan: Methodology; Validation; Writing - Review & Editing; Supervision; Project administration and Funding acquisition.

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