Effect of Fe deficiency on the crystalline structure and magnetic properties of M-type strontium hexaferrite

Ciyu Qin; Yang Sun; Ziyu Li; Ruoshui Liu; Xiaodong Jing; Lichen Wang; Tongyun Zhao; Huayang Gong

doi:10.1016/j.arabjc.2023.105092

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Review article

09 2023

:16;

105092

doi:

10.1016/j.arabjc.2023.105092

Effect of Fe deficiency on the crystalline structure and magnetic properties of M-type strontium hexaferrite

Ciyu Qin^{^a,^b}, Yang Sun^{^a,^b}, Ziyu Li^{^a,^b}, Ruoshui Liu^{^a,^b,^c}, Xiaodong Jing^{^a,^b,^d,^e}, Lichen Wang^{^f,^g}, Tongyun Zhao^{^a,^b,^c}, Huayang Gong^{^a,^b,⁎}

a School of Rare Earths, University of Science and Technology of China, Hefei, Anhui 230026, China

b Ganjiang Innovation Academy, Chinese Academy of Sciences, Ganzhou, Jiangxi 341119, China

c Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

d State Key Laboratory of Multiphase Complex Systems, Beijing Engineering Research Centre of Process Pollution Control, Institute of Process Engineering, Chinese Academy of Sciences, No. 1, 2nd North Street, Zhongguancun, Beijing 100190, China

e University of Chinese Academy of Sciences, Beijing 100049, China

f Ningbo Institute of Materials Technology & Engineering, Chineses Academy of Sciences, Ningbo, Zhejiang 315201, China

g Innovation Center for Applied Magnetics of Zhejiang Province, Ningbo, Zhejiang 315201, China

⁎Corresponding author at: School of Rare Earths, University of Science and Technology of China, Hefei, Anhui 230026, China. gonghuayang@gia.cas.cn (Huayang Gong)

Received: 2023-3-7, Accepted: 2023-6-17,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

In this study, we prepared a single M-type strontium ferrite phase with different iron contents using the traditional ceramic method and studied the effect of iron deficiency on the crystalline structure and magnetic properties of M-type hexaferrite strontium has been studied. With the decrease in iron content, the saturation magnetization of M-type strontium ferrite SrO·nFe₂O₃ powders (5.49 ≤ n ≤ 5.95) decreases by 5.5% and 4.7% at 300 K and 5 K, respectively. The change in Fe³⁺ occupancy was determined using X-ray diffraction spectroscopy. The occupancy of Fe³⁺ in sublattices 2a, 12k and 4f₁ decreased with decreasing Fe content, and the decreased amplitude was in the order 2a > 4f₁ > 12k. In addition, the (4f₁ site) Fe₃-O₂-Fe₅ (12k site) and (4f₁ site) Fe₃—O₂ bond length decreased and increased, respectively, with decreasing Fe content. These results are of great significance for improving the magnetism of SrM by regulating iron vacancies in its structure.

Keywords

Hexaferrite

Iron vacancy

Structure

Magnetic properties

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1 Introduction

Around 1952, Philips Research Laboratories (Went et al., 1952) discovered the M-type hexagonal ferrite, which is a permanent magnet. Hexaferrites account for approximately 80% (Yu et al., 2022) of the commercial permanent magnets in the global magnet market. Compared with the rare earth-based permanent magnets, such as Nd₂Fe₁₄B and SmCo₅, although the maximum remanence and coercivity of MeFe₁₂O₁₉ are lower, its advantages of low cost and chemical stability are irreplaceable. Over the years, the magnetic properties of modified strontium ferrite magnets have increased from typical values (Cochardt, 1963): B_r = 4100 G, _IH_c = 3000 Oe, (BH)_max = 4.0, and MGOe around 1963, to the emergence of high-performance ferrite magnets in 1999. The magnetic properties of anisotropic M-type strontium ferrites (Sr_1-_xLa_xCo_xFe_12-_xO₁₉) containing La and Co were investigated at the TDK Materials Research Center, Japan, around 1999 (Iida et al., 1999). When x = 0.3, the magnetic property of the permanent magnet is greatly improved, and its maximum value reaches B_r = 4.45 kG, H_cJ = 4.82 kOe, (BH)_max = 4.86 MGOe. The temperature dependence of coercivity was also greatly improved, ΔH_cJ/H_cJ/ΔT = 0.1%/°C.

M-type strontium ferrite has a magnetoplumbite structure and belongs to a hexagonal crystal system. It is composed of an R block of a hexagonal dense reactor and an S block of an overlapping cubic dense reactor. Fig. 1 shows a schematic of the strontium ferrite cell (drawn using VESTA), in which Fe³⁺ ions are located at five different crystal sites, represented by symbols 2a, 2b, 12k, 4f_1, and 4f_2, respectively. In M-type permanent magnet ferrites, the ionic magnetic moments of sublattices 2a, 2b, and 12k are arranged parallelly owing to the superexchange interaction. In contrast, the ionic magnetic moments of sublattices 4f₁ and 4f₂ were arranged in reverse, parallel to those of the three sublattices mentioned earlier. With a theoretical Fe³⁺ of 5 μ_B, the resultant experimental net magnetic moment was 40 μ_B per unit cell.

Crystal structure and spin state of M-type strontium hexaferrite.

In 1995, Agotani et al. (Kagotani et al., 1995) proposed a new phase diagram of SrO·nFe₂O₃ (2.0 < n < 6), which has been used to date. They found that the maximum value of the saturation magnetization M_s occurs when n = 5.8; however, the sample contains a small amount of Fe₂O₃, so it cannot be concluded that the lack of Fe improves its magnetic properties. Pablo et al. (de Francisco et al., 1987) prepared SrO·nFe₂O₃ using the ceramic method (n = 5.7, 6). The isochronous detuning spectra indicated the presence of iron-ion vacancies in SrO·5.7Fe₂O₃. They prepared powdered samples of SrO·nFe₂O₃ by glass crystallization (Shirk and Buessem, 1970), chemical coprecipitation (Topal et al., 2007; Rashad et al., 2008), microwave-induced combustion (Fu and Lin, 2005), the SHS route (Nikkhah-Moshaie et al., 2008), and sol–gel techniques (Wang et al., 2009; Salemizadeh and Seyyed Ebrahimi, 2009; Rostami et al., 2018; Mali and Ataie, 2005; Sürig et al., 1996 ) to produce the best magnetism in the range of n < 6. The samples analyzed in these studies exhibit a single M phase when the magnetic properties are optimal. Therefore, it cannot be explained whether the n value or impurity influences the magnetic singleness. However, this indicates that n less than 6 is more conducive to the formation of a single M phase. Synthesis of M-type hexagonal ferrite (BaM) compounds containing excess iron by one-step spark plasma sintering (Zhao et al., 2008a; Zhao et al., 2008b), BaFe₁₂₊_xO_19+1.5_x (0 ≤ x ≤ 0.4). X-ray diffraction showed that the crystalline composition of all the samples in the x range of 0–0.4 was only single-phase BaM. As the x value is increased from 0 to 0.4, σ_s increases. The excess of Fe³⁺ ions in the BaFe₁₂₊_xO_19+1.5_x lattice was confirmed using Raman and FTIR spectroscopy (Zhao et al., 2008a), and this resulted in an enhanced net magnetic moment per unit cell. Many researchers have reported that the Fe/Sr molar ratio (n) is less than 6.0 and in the single M strontium ferrites. In other words, SrFe_xO₁₉ (x < 12) forms more easily. However, the study of iron vacancies and their magnetic change rules has not been considered. Therefore, the effects of iron deficiency on the crystalline structure and magnetic properties of M-type strontium hexaferrites were studied.

In this study, M-type strontium ferrite (SrO·nFe₂O₃, 4.9 ≤ n ≤ 6.0) was prepared by solid phase reaction method to investigate the effect of iron ion content on the structure and magnetism of SrM. This has important guiding significance for reducing material costs and improving process controllability in industrial production.

2 Experimental procedure

2.1

2.1 Synthesis

According to the experimental formula, the use of electronic balance to weigh the purity of 99% SrCO₃ and 99% Fe₂O₃ experimental raw materials (a total of 200 g). The electronic balance used in this experiment has an accuracy of 0.0001 g. The weighed raw material, add a certain quality of steel ball, deionized water together into the horizontal ball mill for raw material mixing for 1 h, the ball: medium: material mass ratio is equal to 12:1.2:1. Note that this process should avoid raw material residues in the vessel as much as possible. Take out the material after ball grinding and place it in the oven to dry, the oven temperature is 90 °C. The material after quantitative drying is placed in the alumina crucible and placed in the high temperature Muffle furnace, according to the time and rate of the preset temperature curve, the highest calcining temperature and the holding time. After calcining, when the Muffle furnace is cooled to room temperature, the calcined products are taken out and ground into micron magnetic powders, which are then characterized by phase and tested for magnetism.

2.2

2.2 Characterizations

The phase purity of the sintered samples was analyzed using X-ray diffraction (XRD) of the power (Bruker AXS D8 Advance) at Cu Kα radiation of λ = 0.15405 nm. EVA and TOPAS software were used to analyze the XRD spectra. The Rietveld method was used to analyze the phase structure of a single M-type strontium ferrite. The concentrations of the elements were measured by X-ray fluorescence (XRF) spectroscopy (ZSXPrimusll+). Raman scattering (RS) spectra were obtained using a laser microscopic confocal Raman spectrometer (Renishaw inVia Raman Microscope) at a wavelength of 532 nm. Magnetic hysteresis loops were measured at 300 K using a superconducting quantum interference device magnetometer (SQUID-VSM). The temperature dependence of the moment (M-T curve) was measured in zero-field cooling (ZFC) mode under a field of 50 kOe.

3 Results and discussion

3.1

3.1 Structural analysis

The phase compositions and structural details of the samples were analyzed using XRD at room temperature. Detailed information on the relative content and crystalline structure of the sample phase was obtained by refining the XRD data using the TOPAS software, with a refinement parameter, R_wp, below 15%, indicating high quality and reliability. When n = 5.4, the powdered sample contained a small amount of the SrFeO₃ phase, as shown in Fig. 2a. Fig. 2d shows the XRD pattern of a representative sample (n = 5.95) as well as the refined results, and the obtained fitting parameter value was R_wp = 12.27%. The minimum sintering temperature of the pure phase increased with increasing iron content (Fig. 2b) because more energy was required to introduce more iron ions into the sublattice of the M phase. The following discussion focuses only on the pure phase samples. The actual iron content (n), which matched the nominal content, was determined using XRF measurements, as shown in Fig. 2c. There is no change rule for the lattice parameter a with respect to n, whereas the lattice constant c decreases with decreasing n, as shown in Fig. 2d and 2e, respectively. The variation in c value is mainly the result of the combined effect of the decrease in the iron ion content and the change in the oxygen ion content.

Refined X-ray diffraction pattern of the sample with (a) n = 5.0 and (d) n = 6.0. (b) phase diagram of SrO·nFe2O3, 5.49 ≤ n ≤ 5.95. (c) Chemical composition for SrO·nFe2O3, 5.49 ≤ n ≤ 5.95. Variations in different lattice constants: (e) a (f) c, (g) c/a, and (h)Vcell. (i)The net magnetic moment of single molecule calculated by refining according to the X-ray spectrum. (j) XRD density of SrO·nFe2O3, 5.49 ≤ n ≤ 5.95.

The TOPAS software was used to refine the occupancy of iron and oxygen ions in the samples using the Rietveld method, as shown in Fig. 3. The Fe ion occupancy of 4f₂ increases with decreasing n. When n = 5.86, it increased by 0.84% to 1. In contrast, The Fe occupancies at the 2a, 4f₁, and 12k (n < 5.7) sites decreased by 2.00%, 1.08%, and 0.51%, respectively. As shown in Fig. 3, the net magnetic moment was calculated by formula. As shown in Fig. 2i, the net magnetic moment increases with n. At n ≥ 5.7, occupancies of O_1 and O_2, which are less than 1, decrease as n decreases, which is due to the decrease of positive ions of iron to ensure chemical valence equilibrium. On the contrary, when n ≤ 5.7, oxygen ion occupancy increases, which may be because the oxygen ions stop decreasing to ensure the structural stability, and small amount of Fe²⁺ is generated to maintain valence equilibrium (Chlan et al., 2015). All the samples have a typical M-type magnetoplumbite structure because c/a is less than 3.98 (Ahn et al., 2013), as shown in the Fig. 2f. The lattice constant c/a decreases as n decreases. Owing to the changes in the lattice constants a and c, the cell volume V_cell first decreases and then increases with increasing n (Fig. 2g). The XRD density (ρ) was calculated using Equation (1) (Yang et al., 2018; Li et al., 2015)

(1)

ρ = \frac{2 M}{{N_{A} V}_{cell}}

Occupancies of (a) iron ions and (b) oxygen ions.

As shown in Fig. 2h, the sample density increased with n. This is because the Fe content increased.

M-type hexagonal ferrites exhibit ferromagnetic structures due to superexchange. The exchange integral is affected by the length and angle of the Fe—O—Fe bond. Table 1 lists the main Fe—O—Fe bond distances and angles in BaFe₁₂O₁₉ and the calculated exchange parameters (Kaur et al., 2006). Among these, the exchange integrals of the (2b site) Fe2-O3-Fe4 (4f₂ site) (two types) and the (4f₁ site) Fe3-O2-Fe5 (12k site) are greater than those of the other two sites. As shown in Fig. 4, with a decrease in Fe content (n), the (2b site) Fe2-O3-Fe4 (4f₂ site) (two types) showed no obvious changes. The bond angle of the (4f₁ site) Fe3-O2-Fe5 (12k site) increased, and the bond lengths of the (4f₁ site) Fe3-O2 and O2-Fe5 (12k site) were shortened and extended, respectively. In contrast, the bond angle of the (4f₁ site) Fe3-O4-Fe5 (12k site) decreases, and the bond lengths of the (4f₁ site) Fe3-O4 and O4-Fe5 (12k site) are extended and shortened, respectively. The variation in the (2a site) Fe1-O4-Fe3 (4f₁ site) is the same as that in the (4f₁ site) Fe3-O4-Fe5 (12k site). This was due to slight changes in the structure caused by changes in ion occupancy, resulting in changes in the bond length and angle.

Table 1 Distances and angles of the Fe-O-Fe bonds and calculated exchange parameters in BaFe₁₂O₁₉.

Bond	Distance (Å)	Angle (degree)	Exchange parameter	Calculated value (K/ $μ_{B}^{2}$ )
(2b)Fe2-O3-Fe4(4f₂) (2b)Fe2-O3-Fe4(4f₂)	1.886 + 2.060 1.886 + 2.060	142.41 132.95	J_bf2	35.96
(4f₁)Fe3-O2-Fe5(12k) (4f₁)Fe3-O4-Fe5(12k)	1.897 + 2.092 1.907 + 2.107	126.55 121.00	J_kf1	19.63
(2a)Fe1-O4-Fe3(4f₁)	1.997 + 1.907	124.93	J_af1	18.15

Main bond angles and bond lengths of SrO·nFe2O3, 5.49 ≤ n ≤ 5.95.

The dynamic behavior of the cations at various sites and their distributions were investigated using Raman spectroscopy. For a typical SrM, there are 64 ions in a cell, of which 24 Fe³⁺ ions are located at tetrahedral sites (FeO4), bipyramidal sites (FeO5), and octahedral sites (FeO6). Among the 189 optical modes associated with M-type hexaferrites, 42 active Raman submodes (11A1g + 14E1g + 17E2g) were found according to group theory (Kreisel et al., 1998; Kreisel et al., 1999; Buzinaro et al., 2019; Nguyen et al., 2021 ).

Room-temperature Raman spectra of SrO·nFe₂O₃ (5.49 ≤ n · 5.95) were obtained in the range of 150–850 cm⁻¹, as shown in Fig. 5. The modes of RS spectrum are 177, 213, 333, 405, 525, 611, 679, and 720 cm⁻¹. The vibration modes at 177 cm⁻¹ were attributed to the spinel structure, and the 213 cm⁻¹ mode was attributed to either E1g or E2g symmetry (O—Fe—O bridge). The vibration modes at 333 cm⁻¹ are associated with octahedra (FeO6, 12k and 2a site) and is attributed to mixing of A1g and E1g; those at 525 cm⁻¹ are attributed to E2g symmetry. The vibration modes at 405, 611, 679, and 720 cm⁻¹ are associated with (Fe⁽⁵⁾O6, 12k site) octahedra, octahedra (Fe⁽⁴⁾O6, 4f₂ site), bipyramid (Fe⁽²⁾O5, 2b site), and tetrahedra (Fe⁽¹⁾O4, 4f₁ site), respectively, all of which exhibit A1g symmetry (Buzinaro et al., 2019; Nguyen et al., 2021; Almessiere et al., 2021 ).

Raman spectra of SrO·nFe2O3, 5.5 ≤ n ≤ 6.0.

The mass and force constants affect the shift of the peaks in the Raman spectrum. A reduction in Fe³⁺ occupancy in SrM results in variations in the ionic mass and force constants; these changes are based on the bond length, lattice parameters, covalence, etc.. At 333 cm⁻¹ (octahedron, 12k and 2a sites) and 720 cm⁻¹ (tetrahedron, 4f₁ site), the band wavenumber is widened and shifted slightly towards lower wavenumbers as n decreased. As Fe occupies less mass at the 12k and 2a sites, the Raman peak shifts slightly towards a lower wavenumber. In contrast, changes in the bond length and angle cause the local tetrahedrons and octahedrons to deform, resulting in wider Raman peaks corresponding to that location. The shifting and broadening of amplitudes of the Raman peaks was more significant at 333 cm⁻¹ (octahedron, 12k and 2a site) than at 720 cm⁻¹ (tetrahedral, 4f₁ sites). This is because the largest change in Fe is observed at position 2a. Additionally, with a decrease in iron content, a small amount of Fe²⁺ appeared to maintain the chemical valence balance. Raman peaks at 679 and 611 cm⁻¹ represent bipyramidal and octahedral modes, respectively. Neither of these peaks changed as n decreased, indicating that the changes in Fe at sites 4f₂ or 2b were insignificant. Moreover, the Raman peak at 177 cm⁻¹ does not change as n decreases. The results showed that the Fe content had no obvious effect on the vibration mode of the entire spinel block.

3.2

3.2 Magnetic properties

The M-H curves of SrO·nFe₂O₃ (5.49 ≤ n · 5.95, with increments of 0.1) were measured at 300 K in the applied magnetic field range of 0–50 kOe (Fig. 6a). The relevant magnetic parameters are presented in Table 2. A Stoner-Wohlfarth (SW) adjustment was used to determine the saturation magnetization. Fig. 6b shows the M-H curve of SrO·5.95Fe₂O₃. Based on the law of saturation approximation, the simplified SW model can be used to extract M_s values (Almessiere et al., 2021; Grössinger, 1981).

(2)

M = M_{s} (1 - \frac{A}{H} - \frac{B}{H^{2}}) + χ_{P}

(a) Magnetizing curve of SrO·nFe2O3, 5.49 ≤ n ≤ 5.95. (b) Experimental and fitted moment versus H curves in the range of 20 kOe to 50 kOe for the sample with n = 5.95. (c) Variation in Ms for SrO·nFe2O3, 5.49 ≤ n ≤ 5.95, at 300 K. (d) HA and K1 for SrO·nFe2O3, 5.49 ≤ n ≤ 5.95. (e) M-T curves of SrO·nFe2O3, 5.49 ≤ n ≤ 5.95. (f) Variation in M5T for SrO·nFe2O3, 5.49 ≤ n ≤ 5.95, at 5 K. (g) Relative molecular mass of SrO·nFe2O3, 5.49 ≤ n ≤ 5.95. (h) The net magnetic moment of a single molecule calculated from M5T obtained at 5 K

Table 2 Values of A, B, χ_p, R², H_A, and k₁ of the M-type SrO·nFe₂O₃(5.49 ≤ n ≤ 5.95) ferrite samples obtained from the fitting data (Fig. 6).

n	M_s(emu/g)	A( $\times$ 10²)	B( $\times$ 10⁷)	χ_p( $\times$ 10^-5)	R²	H_A(Cal.)(kOe)	k₁(kOe*emμ/g)
5.95	79.18	3.27	4.03	3.26	0.99992	24.59	973.3828
5.9	78.16	6.68	4.01	3.32	0.99999	24.52	958.4564
5.86	76.88	6.76	4.00	3.13	0.99998	24.49	941.5839
5.7	75.74	5.37	3.83	2.89	0.99998	23.96	907.6958
5.6	74.61	6.04	3.70	3.14	0.99998	23.55	878.8475
5.49	73.8	6.95	3.68	3.10	0.99999	23.49	866.9537

Here, M_s denotes saturation magnetization, A indicates inhomogeneity, χ_p represents high field susceptibility, and B denotes anisotropy. Kagotani et al (Went et al., 1952) studied the Magnetic Properties of SrO·nFe₂O₃(0.5 ≤ n ≤ 6.0)and Phase Diagram in SrO-Fe₂O₃ System, SrO·nFe₂O₃(0.5 ≤ n ≤ 6.0) gave magnetic properties Ms is 50–75 emu/g in the n-range of n = 6.0–2.0. In our manuscript, SrO·nFe₂O₃(5.49 ≤ n ≤ 5.95) gave magnetic properties M_s is 73.8–79.18 emu/g in the n-range of n = 4.9–6.0. As shown in Fig. 6c, M_s initially decreased by 6.8% from 79.18 emu/g (n = 5.95) to 73.8 emu/g (n = 5.49). The reason for this decline is that the share of Fe decreased at the 2a, 12k and 4f₁ sites, with the largest decline at the 2a site. In addition, after n = 5.6, Fe²⁺ with a lower magnetic moment (4 μ_B) occupied the 2a site. This results in a decrease in the net magnetic moment. The net magnetic moment in the crystalline state is related to the following mathematical expression:

(3)

m = 6 m_{12 k} + m_{2 a} + m_{2 b} - 2 (m_{4 f 1} + m_{4 f 2})

The net magnetic moment of a single molecule was calculated based on the occupancy of Fe at each position (Fig. 3), as shown in Fig. 2i. The net magnetic moment decreased by 1.1% from 20.14 μ_B/f. u. (n = 5.95) to 19.92 μ_B/f.u. (n = 5.49). The M-T curve of SrO·nFe₂O₃ (5.49 ≤ n · 5.95) was measured in the temperature range of 5–300 K at 50 kOe in an external field (Fig. 6e). The relationship between magnetization and temperature can be observed. At 5 K, M_5T decreased by 4.7% from 112.20 emu/g (n = 5.95) to 106.92 emu/g (n = 5.49). The formula for the magnetic moment per unit was calculated using Equation (4) (da Silva-Soares et al., 2022), where M_r and M_s represent the molar mass and saturation magnetization, respectively. The molar mass and magnetic values for all the components are shown in Fig. 6e and h.

(4)

m = \frac{M r M s}{5585}

The net magnetic moment decreased from 20.34 μ_B/f. u (n = 5.95) to 19.74 μ_B/f.u (n = 5.49). These conclusions were verified once again. Furthermore, for crystalline structures with hexagonal symmetry, B can be expressed as:

(5)

B = \frac{H_{A}^{2}}{15} = \frac{4 K_{1}^{2}}{15 M_{S}^{2}}

where, H_A is the anisotropy field, and K₁ is the magnetocrystalline anisotropy constant. As shown in Fig. 6h, K1 and H_A decreased with decreasing n. Because of the decrease in Fe content, the occupancy of Fe³⁺ in sublattices 2a, 12k and 4f₁ decreased, and the decrease in amplitude was in the following order: 2a > 4f₁ > 12k. In addition, the (4f₁ site) Fe3-O2-Fe5 (12k site) bond angle and (4f₁ site) Fe3—O2 bond length decreased and increased, respectively.

4 Conclusions

In this paper, M-type strontium ferrite phases with different amounts of iron ions were prepared, and their phase formation, crystal structure and magnetic properties were systematically studied. When n = 5.5 ∼ 6.0, single-phase SrM samples can be generated, and the required calcination temperature increases with the increase of n value, indicating that more energy is required to enable Fe³⁺ to enter the sublattice of M-type strontium ferrite. The measurement of the specific saturation magnetization (σs) of M-type strontium ferrite SrO·nFe₂O₃ (5.5 ≤ n ≤ 6.0) shows that σs increases with the increase of iron ion content. In the process of n = 5.5 to 6.0, the increase was 5.5% and 4.7% at 300 K and 5 K, respectively. In the crystal structure observation, the occupancy of Fe³⁺ in the 2a, 12k and 4f₁ sublattice of SrM decreases with the decrease of n value by 2a ＞4f₁ ＞12k, the absence of Fe³⁺ in the SrM sublattice leads to a decrease in σs. In addition, the bond Angle (4f₁) Fe3-O2-Fe5 (12k) and bond length (4f₁) Fe3-O2 decrease and increase with the decrease of n value, respectively.

Acknowledgements

We gratefully acknowledge financial support from the Key Research Program of the Chinese Academy of Sciences (Grant No. ZDRW-CN-2021-3) and the grant from the Research Projects of Ganjiang Innovation Academy, Chinese Academy of Sciences (E055B002).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Yu X., . Simultaneous improvement of coercivity and saturation magnetization of M-type strontium ferrite by Nd³⁺-Co²⁺ unequal co-substitution. Ceram. Int. 2022
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Zhao W., . Evidence and role of excessive iron in the lattice of M-type barium hexaferrite synthesized by one-step spark plasma sintering method. Scr. Mater.. 2008;59(3):282-285.
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Zhao W.Y., . Lattice vibration characterization and magnetic properties of M-type barium hexaferrite with excessive iron. J. Appl. Phys.. 2008;103(6):063902
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Introduction

Experimental procedure

Synthesis
Characterizations

Results and discussion

Structural analysis
Magnetic properties

Conclusions

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[Google Scholar]

[20] Rostami Z.A., Mousavi Ghahfarokhi S.E., Kazeminezhad I., . Effect of Fe/Pb molar ratio on the structure, magnetic and dielectric properties of PbFe₁₂O₁₉ nanoparticles. Chin. J. Phys.. 2018;56(2):760-769.
[Google Scholar]

[21] Salemizadeh S., Seyyed Ebrahimi S.A., . Influence of Fe/Ba ratio, basic agent and calcination temperature on the physical properties of nanocrystallineline barium hexaferrite thin films prepared by a sol–gel method. J. Non-Crystall. Solids. 2009;355(16–17):982-985.
[Google Scholar]

[22] Shirk B.T., Buessem W.R., . Magnetic properties of barium ferrite formed by crystallinelization of a glass. J. Am. Ceram. Soc.. 1970;53(4):192-196.
[Google Scholar]

[23] Sürig C., Hempel K.A., Sauer C., . Influence of stoichiometry on hexaferrite structure. J. Magn. Magn. Mater.. 1996;157–158:268-269.
[Google Scholar]

[24] Topal U., Ozkan H., Dorosinskii L., . Finding optimal Fe/Ba ratio to obtain single phase BaFe₁₂O₁₉ prepared by ammonium nitrate melt technique. J. Alloy. Compd.. 2007;428(1–2):17-21.
[Google Scholar]

[25] Wang Y., . Effect of Fe/Sr mole ratios on the formation and magnetic properties of SrFe₁₂O₁₉ microtubules prepared by sol–gel method. J. Magn. Magn. Mater.. 2009;321(19):3368-3372.
[Google Scholar]

[26] Went J.J., . Hexagonal iron-oxide compounds as permanent-magnet materials. Phys. Rev.. 1952;86(3):424-425.
[Google Scholar]

[27] Yang Y., . Effects of Bi₂O₃ - Nb₂O₅ additives on microstructure and magnetic properties of low-temperature-fired NiCuZn ferrite ceramics. Ceram. Int.. 2018;44(9):10545-10550.
[Google Scholar]

[28] Yu X., . Simultaneous improvement of coercivity and saturation magnetization of M-type strontium ferrite by Nd³⁺-Co²⁺ unequal co-substitution. Ceram. Int. 2022
[Google Scholar]

[29] Zhao W., . Evidence and role of excessive iron in the lattice of M-type barium hexaferrite synthesized by one-step spark plasma sintering method. Scr. Mater.. 2008;59(3):282-285.
[Google Scholar]

[30] Zhao W.Y., . Lattice vibration characterization and magnetic properties of M-type barium hexaferrite with excessive iron. J. Appl. Phys.. 2008;103(6):063902
[Google Scholar]

Effect of Fe deficiency on the crystalline structure and magnetic properties of M-type strontium hexaferrite

Abstract

Keywords

Hexaferrite

Iron vacancy

Structure

Magnetic properties

1 Introduction

2 Experimental procedure

2.1 Synthesis

2.2 Characterizations

3 Results and discussion

3.1 Structural analysis

3.2 Magnetic properties

4 Conclusions

Acknowledgements

Declaration of Competing Interest

References

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