M-type Strontium Ferrite Research Articles

Mechanism of praseodymium yttrium regulating the absorption properties of M-type strontium ferrite: From single phase to multi phase mixed system

When Pr and Y ions are added to M-type strontium ferrite, a portion of the ions will enter the main phase lattice, while the excess ions will aggregate at the grain boundaries to form a secondary phase. The occupancy of rare earth ions in the main phase lattice and the formation of secondary phases are two key factors affecting the material's absorbing properties. The difference in ultimate solid solubility between rare earth ions Pr and Y in M-type strontium ferrite is significant, and they also form different secondary phases at grain boundaries. Consequently, the synthesized SrFe12-2xPrxYxO19 (0 < x ≤ 1.5) demonstrates its potential as a microwave absorbing material across a wide range of substitutions. Moreover, the performance changes have their own characteristics at different substitution levels. XRD results show that the samples include pure M phase and the coexistence of M phase and heterogeneous phases, with the heterogeneous phases being perovskite-type and garnet-type. SEM and EDS results indicate that Pr and Y co-substitution can refine grain size and reduce oxygen content. XPS results suggest that the valence change of Pr ions leads to the generation of Fe2+ ions and oxygen vacancies (Od). PPMS results reveal that saturation magnetization and coercivity are mainly affected by anisotropy field and particle size. Co-substitution of Pr and Y increases the dielectric and magnetic losses of the M phase, and the generated heterogeneous phases also enhance the dielectric and magnetic losses through interface polarization and magnetic exchange coupling effects, both cooperatively improving the wave-absorbing performance, with the minimum reflection loss (RLmin) reaching −51.57 dB (x = 0.1, d1 = 4.0 mm, EAB = 2.57 GHz).

Impact of Co2+ substitution on structure and magnetic properties of M-type strontium ferrite with different Fe/Sr ratios

Abstract Ion substitution has significantly improved the performance of ferrite magnets, and cobalt remains a key area of research. Studies on the mechanism of Co2+ in strontium ferrite, especially SrFe2n–x Co x O19–δ (n = 6.1–5.4; x = 0.05–0.20) synthesized using the ceramic method, showed that Co2+ preferentially enters the lattice as the Fe/Sr ratio decreases. This results in a decrease in the lattice constants a and c due to oxygen vacancies and iron ion deficiency. The impact of Co substitution on morphology is minor compared to the effect of the Fe/Sr ratio. As the Fe/Sr ratio decreases and the Co content increases, the saturation magnetization decreases. The magnetic anisotropy field exhibits a nonlinear change, generally increasing with higher Fe/Sr ratios and Co content. These changes in the performance of permanent magnets are attributed to the absence of Fe3+ ions at the 12k + 2a and 2b sites and the substitution of Co2+ at the 2b site. This suggests that by adjusting the Fe/Sr ratio and appropriate Co substitution, the magnetic anisotropy field of M-type strontium ferrite can be effectively optimized.

Praseodymium dysprosium co-doped M-type strontium ferrite: Intentionally manufacturing heterophase growth to improve microwave absorption performance

When excessive praseodymium and dysprosium ions are doped with M-type strontium ferrite, heterophases with different magnetic and electrical properties will be formed. We use this to intentionally induce different heterogeneous growth in the Pr–Dy co-doped strontium ferrite system. While maintaining the dielectric loss of the main phase, the produced heterogeneous phase acts as a companion for dielectric and magnetic losses. The synthesized SrFe12-2xPrxDyxO19 ferrite demonstrates its potential as a microwave absorbing material, exhibiting excellent absorption effects over a wide range of Pr–Dy doping (x = 0.05–1.5). The XRD results show that the synthesized materials include both pure M-phase and coexistence of M-phase and heterophases, and the generated heterophases are mainly perovskite type ferrite and garnet type ferrite. SEM and EDS results indicate that Pr–Dy co-doping can significantly refine the grain size, reduce the grain size of the main and heterophases, and lead to a decrease in oxygen content. The XPS analysis shows that some praseodymium ions are in the Pr4+ oxidation state, leading to the existence of Fe2+ ions and oxygen defects (Od). The VSM results indicate that at different calcination temperatures, the saturation magnetization decreases and the coercivity shows an increasing trend as the Pr–Dy doping amount increases. Pr–Dy doping not only increases the dielectric and magnetic losses of the M phase, but also generates heterophases that can enhance the dielectric and magnetic losses of the material, jointly improving the absorption effect. This results in excellent absorption performance of the material within a large range of praseodymium dysprosium doping contents (x = 0.05–1.5, RLmin = −52.51 dB, EABmax = 4.81 GHz).

Effect of the interaction of Fe- and Ce-contents on the structure and magnetic properties of M-type strontium ferrites

Sr1-xCexFe12O19 and Sr1-xCexFe12-yO19-δ (x = 0–0.2, y = 0–2) powders were synthesized by sol-gel auto-combustion method, and the effect on the structure and magnetic properties of changes in doping concentration and iron content has been investigated. XRD results confirmed the formation of M phase and impurities of CeO2 and Fe2O3. The SEM results show that cerium doping leads to a decrease in grain size. For Sr1-xCexFe12O19, the saturation magnetization increases to 77.73 emu/g first and then decreases with the increase of cerium doping. More importantly, our study also found that as the Ce doping concentration and iron content change, the interaction between the two changes differently. This interaction will have different effects on the occupancy of iron ions at spin-up and spin-down sites, ultimately leading to a significant characteristic change in magnetic properties. For Sr1-xCexFe12-yO19-δ, with the iron content decreases, the magnetic properties continue to decrease at x = 0.03, increase first and then decrease at x = 0.1, and keep improving at x = 0.2. It is of reference significance to change the magnetic properties of strontium ferrites by adjusting the relationship between rare earth doping concentration and iron content.

Effect of post-annealing on magnetic anisotropy in La–Co co-substituted M-type strontium ferrite

We investigated the effect of post-annealing on the magnetic anisotropy in La–Co co-substituted magnetoplubite-type strontium ferrite, a matrix phase of commercial high-performance ferrite magnets. Post-annealing was found to be effective in controlling the distribution of substituted Co2+. The Co2+ distribution obtained by lower-temperature annealing shows higher magnetic anisotropy, suggesting that uniaxial magnetic anisotropy is enhanced only when Co2+ occupies the most stable occupied site, i.e., the 4f1 site in the tetrahedral coordination. Furthermore, the slower the cooling rate, the higher the anisotropy. The temperature-dependent Co2+ distribution predicted from the reported density functional theory calculations was compared with the actual anisotropy after annealing, yielding +2.3 meV/ion as the Co2+ anisotropy constant at the tetrahedrally coordinated site and −1.2 meV/ion as that at the octahedrally coordinated sites. Careful selection of heat treatment conditions leads to efficient use of cobalt, an element with supply risks.

Facile synthesis of novel hexagonal strontium ferrites for promising adsorption of cadmium from aqueous solutions

Cadmium (Cd(II)) contamination in both the surface and ground water is threatening the lives of millions of people across the world. In this work, we have hydrothermally synthesized the novel multiphase (MP) and single phase (SP) M-type hexagonal strontium ferrites (SF, SrFe12O19) for removing Cd(II) from contaminated water. The as-synthesized materials were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectrometry (XPS). The MP-SF and SP-SF demonstrated excellent Cd(II) adsorption capacities over wide pH range. The pseudo-first and second-order kinetics models as well as the Langmuir and Freundlich isotherms models were used for fitting the experimental data for adsorption of Cd(II) on both the MP-SF and SP-SF. The maximum adsorption capacities reached to 57.5 and 78.9 mg/g for the MP-SF and SP-SF, respectively, at pH 7, which were better than many recently reported magnetic adsorbents. The effects of common co-existing ions on the adsorption capacities of both the MP-SF and SP-SF were also evaluated. FTIR and XPS spectroscopic analyses further confirmed that Cd(II) was adsorbed on to the surface of SP-SF through the formation of an inner-sphere complex between the Cd(II) and surface metal centers.Furthermore, the as-synthesized materials were employed for the treatment of simulated real Cd(II) contaminated water. The experimental results suggested that the SP-SF could be a strong candidate for practical applications of Cd(II) removal from aqueous solutions.

Single-Domain Hard Ferromagnetic M-SrFe Nanoparticles for Magnetic Data Storage

Single-domain M-type Strontium Ferrite nanoparticles are prepared by the co-precipitation method. The crystallite size of the M-SrFe Nps is 58.1 nm, as determined by the XRD pattern. The SEM micrographs reveal the hexagonal morphology. M-SrFe Nps is depicted in EDS analysis. According to VSM characterization, the sample is a hard magnetic material with high coercivity. With its outstanding magnetic characteristics, hexaferrite is typically employed in permanent magnetic materials and recording devices. The band gap energy is determined to be 1.95 eV from the UV-DRS reflectance data using the Kubelka-Munk plot. The absorbed wavelength with the highest intensity peak in PL analysis is 629.9 nm. The TG-DTA investigations support the remarkable thermal stability of M-SrFe Nps. The resistivity of the sample, 0.312 Ωm is calculated using the four-probe method.

Ca-Co co-doped strontium ferrite ceramic with tunable magnetic properties for enhanced microwave absorbing application

M-type strontium ferrite (SrFe12O19), due to its excellent thermal stability, corrosion resistance, resistivity, curie temperature, and magnetic anisotropy, should be an ideal candidate for designing microwave absorbers, and the only obstacle is its unsatisfied magnetic properties. Herein, we proposed a co-doping strategy to tune the magnetic properties of SrFe12O19, namely Ca-Co co-substituted SrFe12O19 (CaxSr1-xFe12-xCoxO19; x ≤ 0.4), which is fabricated via a solid phase sintering process. By changing the co-doping ratio (x = 0.1, 0.2, 0.3, and 0.4), the magnetic properties were well regulated, including saturation magnetization (41.70∼57.92 emu⋅g − 1), coercivity (156.507∼291.747 Oe), and magneto-anisotropy constant (1.476∼2.409×106 erg/cm3). As initially expected, the CaxSr1-xFe12-xCoxO19 (x = 0.) ceramic show good microwave absorbing performance, for example, an optimal reflection loss of −21.3 dB and an effective absorbing bandwidth of 4.8 GHz at a sample thickness of 2 mm was achieved. Such results demonstrate the validity of the co-doping strategy in designing microwave absorbers with high performance based on M-type ferrite.

Utilizing ultrapure magnetite concentrate for environmentally friendly and low-cost synthesis of high-performance strontium ferrite

The presence of Al and Si impurities from ultrapure magnetite concentrate (UMC) entering the lattice during the preparation of M-type strontium ferrite (SrM) has been a significant issue limiting the enhancement of magnetic properties in UMC- prepared SrM. In this article, the impact of CaCO3 on the phase formation mechanism of synthesizing SrM using UMC is investigated. It is found that the formation of intermediate SrFeO3−x phase and SrFe12O19 phase shifts to the lower temperatures upon CaCO3 addition. Lower calcination temperatures can inhibit excessive grain growth, thereby improving coercivity. At a calcination temperature of 1050 °C with the addition of 0.6 wt% CaCO3, the highest coercivity of 4672.29 Oe was achieved. Lattice parameters, magnetic properties, and micro-area composition analysis demonstrate that the addition of CaCO3 reacts with Al impurities, preventing the incorporation of Al ions into the SrM lattice and promoting an increase in saturation magnetization. The highest saturation magnetization of 71.45 emu/g was obtained at the calcination temperature of 1200 °C. It has reached the level of magnetic properties of SrM prepared from Fe2O3. CaCO3, being low-cost and environmentally friendly, can serves as an effective additive for improving the magnetic properties of UMC-prepared SrM without compromising its cost-effective and eco-friendly advantages.

Magnetic Properties of M-Type Hexagonal Ferrite: Mechanical Applications

As the information era continues to advance at a rapid pace, M-type strontium ferrite and other magnetic materials are finding more and more traditional uses. Numerous industries rely on it as a permanent magnet material because of its inexpensive cost, ease of preparation, and outstanding overall performance in areas including electronics, national defense, and communication. In this paper, we investigate some the magnetoelectric coupling properties at room temperature by solid phase method and sol-gel method. The phase structure was determined using an X-ray diffractometer, and the samples were all single-phase polycrystalline with a spatial group of P63/mmc. Observing the surface morphology using field emission scanning electron microscopy, it was found that the composition distribution of the samples prepared by solid-phase method was uneven and there was a "scandium rich phase". The samples prepared by the sol gel method have uniform composition distribution, hexagonal grain shape, and grain size of about 3-5 μ M. The magnetic properties of the samples prepared by the sol gel method and the solid phase method were studied, respectively. The results showed that the phase transition occurred in the solid phase method at about 250K, and the hysteresis loop at room temperature did not show the magnetoelectric coupling behavior. The magnetic phase transition of the sample prepared by the sol gel method occurred near 330K. Combined with the research on the hysteresis loops of the temperature above and below this phase transition point, it shows that this phase transition corresponds to the change of the ferromagnetic to the conical magnetic structure. The similar relationship between magnetic capacitance and magnetization intensity with magnetic field indicates that this conical magnetic structure can induce ferroelectric polarization, which can be understood based on the inverse Dzyaloshinskii-Moriya model.

Enhancement of microwave absorption properties of SrxFe12-yPr0.4o19-θ (x=0.6–1.3, y=0∼0.4) by tuning the calcination temperatures

SrxFe12-yPr0.4O19-θ (x = 0.6–1.3, y = 0∼0.4) powders have been synthesized by the sol-gel auto-combustion method. The effect of iron and strontium ion content and calcination temperatures on the structure, magnetic properties and microwave absorption properties has been studied. The X-ray diffraction patterns of samples confirm the formation of M-type strontium ferrite and indicate that the secondary phases change with the increase of calcination temperature and strontium content, thereby affecting the structure and properties of the material. XPS and Raman spectrum analysis shows that some praseodymium ions are in the Pr4+ oxidation state, leading to the existence of Fe2+ ions and oxygen defects (Od), which can certainly affect the magnetic and dielectric properties of the materials. The VSM results show that the saturation magnetization first increases and then decreases with the increase of strontium content at different calcination temperatures and Sr0·8Fe11.8Pr0.4O19-θ has obtained the maximum saturation magnetization of 81.20 emu/g and the coercivity of 4100 Oe. Increase in strontium content not only promotes the reaction, but also generates a second phase FePrzSr1-zO3-δ, increasing the dielectric and magnetic losses of the materials. The maximum reflection loss reaches −66.77 dB and the maximum effective absorption bandwidth is 4.76 GHz. Therefore, on the one hand, the valence state changes of some praseodymium ions result in the generation of Fe2+ ions and oxygen vacancies, thereby increasing dielectric and magnetic losses. On the other hand, the change of the second phases also affects the absorption performance of the material. ɑ-Fe2O3 is not conducive to improving magnetic and absorption properties, and PrFeO3 may improve magnetic properties. Perovskite type PrzSr1-zFeO3-δ has a large number of ion valence state changes inside, leading to increased dielectric and magnetic losses, which is beneficial for improving the absorption performance of the materials.

The influence of Ho doping on the morphology and magnetic properties of M-type strontium ferrite with different Fe/Sr

Ho-doped strontium ferrite powder samples with different Fe/Sr ratio were successfully prepared by sol-gel auto-combustion method. Different Fe/Sr ratios (Sr1-xHoxFe12O19, Sr1-x/2HoxFe12-x/2O19, SrHoxFe12-xO19, Sr1+xHoxFe12-xO19, Sr1+xHoxFe12-2xO19) were designed to study the influence of Ho doping on the morphology and magnetic properties of M-type strontium ferrite. XRD analysis revealed a relative change in the content of the secondary phases Fe2O3, HoFeO3, and SrFeO3-x in Ho-doped samples as the Fe/Sr ratio varies. The excess of Sr and Fe in the internal environment resulted in such changes in the phase. SEM analysis confirmed that Ho doping led to an increase in grain size. Different doping methods could lead to significant difference in the size of crystal grain. XPS results indicated that the secondary phases caused by Ho doping led to a change in the oxidation state of the iron element. It was inferred from FTIR and Raman spectra that Ho doping into the lattice might occupy both 2b and 4f1 sites. The VSM showed that under the SrHoxFe12-xO19 doping mode (x = 0.05–0.2), the obtained samples showed a decrease in coercivity (Hc) with increasing Ho doping level (from 5.26 to 4.78 kOe), and the saturation magnetization (Ms) also decreased (from 76.73 to 73.28 emu/g). As the Fe/Sr ratio gradually increases, the saturation magnetization of the sample shows a trend of first increasing and then decreasing, while the coercivity shows a trend of first decreasing and then increasing. The intermediate ionic radius of Ho3+ (0.89 Å) among the rare earth elements results in its unique occupancy behavior, which also influences the formation of different phases, resulting in corresponding changes in coercivity and saturation magnetization.

Properties of Sm–Mn substituted M-type strontium ferrites synthesized by the sol-gel method

M-type strontium ferrites Sr1-xLnxFe12-xMxO19 (Ln: Sm; M: Mn; x = 0, 0.03, 0.06, 0.09, 0.12) doped with equivalent Sm-Mn ions were synthesized via the sol-gel method. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electric microscopy (SEM) and vibrating sample magnetometer (VSM). The samples with x from 0.00 to 0.12 were confirmed to the single-phase M-type strontium ferrite, and the impurity phases Fe2O3 and SmFeO3 were detected when the content of dopants x ≥ 0.09. When x = 0.09, the saturation magnetization (Ms) and the remanent magnetization (Mr) of strontium ferrites Sr1-xSmxFe12-xMnxO19 reached to the maximum values of 37.19 emu/g and 22.48 emu/g, respectively. When x = 0.06, the coercive force (Hc) of strontium ferrites Sr1-xSmxFe12-xMnxO19 reached to the maximum values of 6224 Oe. Acid-treatment reduces the magnetic properties of the Sr1-xSmxFe12-xMmxO19 (x = 0.03). Compared to 950 °C preparation, preparation at 1200 °C decreases its magnetic properties and the Hc drop is very significant.

Role of oxygen potential in dopant solubility in ferrite magnets: Enhanced Zn solubility and magnetization in La–Zn co-substituted magnetoplumbite-type strontium ferrite

To improve the performance of magnetoplumbite-type (M-type) AFe12O19 (A = Sr, Ba, Pb,…) hard ferrite magnets, such as the remanent magnetization and the coercivity, it is effective to dope transition metal elements at the Fe site. Substitution of nonmagnetic Zn, which preferentially occupies a minority-spin site in the ferrimagnets, is expected to increase magnetization. However, the solubility of Zn is limited to approximately 2–3% of Fe when synthesized in air. The solubility of divalent transition-metal substituents achieved by simultaneous substitution with trivalent cations on the A-site is often limited due to the auto reduction of Fe3+ to Fe2+. In this study, La–Zn co-substituted M-type strontium ferrites, Sr1−xLaxFe12−yZnyO19, were synthesized under different oxygen pressures of pO2 = 0.2, 1, and 10 atm, and the phase equilibrium and chemical composition were established by X-ray diffraction and wavelength dispersive X-ray spectroscopy. At pO2 = 10 atm, Sr-free La–Zn co-substituted ferrite, LaFe11.25Zn0.75O19, and single phases with actual compositions (x, y) = (0.42, 0.33) and (0.50, 0.45) were obtained for the first time. The single-phase samples exhibited a 5–9% higher saturation magnetization compared to non-doped SrFe12O19 at room temperature. Together with the coercivity enhancement by Co2+ substitution, oxygen potential control is a promising strategy to tune both coercivity and magnetization in future ferrite magnets.

Structural and magnetic properties of BaFe9.95Al2Mg0.05O19 tuned through sintering temperature

The sintering temperature is a key way to tune the structural and magnetic properties of M-type hexaferrites. Here the effect of BaFe9.95Al2Mg0.05O19 M-type hexagonal Ba-hexaferrites, was studied. X-ray diffraction analysis revealed the presence of Fe2O3 impurity phases in all samples. The results showed that as the sintering temperature increased, the saturation magnetization (Ms) and remanence ratio (Mr/Ms) initially increased, then decreased at higher temperatures. On the other hand, the coercivity (Hc) and magnetocrystalline anisotropy field (Ha) decreased first, then increased. The average grain size (D) consistently grew between 800–2800 nm with increase in pre-sintering temperature. The optimal magnetic properties of BaFe9.95Al2Mg0.05O19 were achieved at a pre-sintering temperature of 1280 °C, with Ms = 49.94 emu g−1, Hc = 4.99 kOe, Ha = 1.5 kOe, and mB = 9.4097 μB. The findings suggest that magnetic properties of M-type hexagonal strontium ferrite can be significantly enhanced by optimizing the pre-sintering temperature, which has implications for the development of high-performance self-biased circulators, Magnetic filters and other magnetic applications.

Effect of praseodymium valence change on the structure, magnetic, and microwave absorbing properties of M-type strontium ferrite: the mechanism of influence of citric acid dosage and calcination temperature

SrFe12-xPrxO19(x = 0–0.5) powders were synthesized and the effects of praseodymium doping amount, citric acid dosage, and calcination temperature on its structure, magnetic properties, and microwave absorbing properties were studied. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that praseodymium doping leads to the lattice expansion and makes strontium ferrite easier to form spherical polyhedron in microscopic morphology. The Fe2O3 impurity phase disappears and FePr1-ySryO3-δ impurity phase appears with the increase of the calcination temperature. It was inferred from Raman spectra and X-ray photoelectron spectroscopy that some Pr3+ ions form Pr4+ ions and the latter may occupy iron or strontium sites, and the transition from the Fe3+ to Fe2+ may occur at 4f2 site. The vibrating sample magnetometer results show that the saturation magnetization decreases first and then increases; the coercivity increases and the anisotropy field decreases after doping praseodymium. Praseodymium-doped strontium ferrite has strong absorption in low frequency band (C-band) or medium frequency band (X-band), while the matching thickness corresponding to high frequency band (Ku-band) is small. The maximum reflection loss reaches −50.95 dB and the effective absorption bandwidth (RL < −10 dB) is 4.76 GHz. Increasing the calcination temperature or doping amount will reduce the matching thickness, while increasing the amount of citric acid will disperse the grains and reduce the dielectric loss. It can be concluded that praseodymium valence change leads to the increase of Fe2+ ions and oxygen defects and there is also interface polarization between M-phase and heterogeneous phase, which together increases the dielectric loss of the material. Meanwhile, praseodymium doping can significantly increase the magnetic loss caused by natural resonance. These show that praseodymium doping improves the impedance matching of the material, increases the attenuation constant, and significantly improves the wave absorption performance.

Absorption-Dominant mmWave EMI Shielding Films with Ultralow Reflection using Ferromagnetic Resonance Frequency Tunable M-Type Ferrites

HighlightsA novel multi-band absorption-dominant electromagnetic interference (EMI) shielding film with transition metal-doped M-type strontium ferrites composite layer and a conductive grid is developed.This film shows (1) ultralow EMI reflection less than 5%, (2) in multiple mmWave frequency bands corresponding to ferrites and grid characteristics, (3) with a broadband EMI shielding performance over 99.9% from 40 to 90 GHz.

Structure and magnetic properties of Al3+ substituted M-type SrLaCo hexaferrite

M-type hexagonal ferrites (SrFe12O19) have attracted much attention as a widely used permanent magnet. Many studies have been done to improve permanent magnetic properties. In particular, the formula of La–Co co-replaced Sr–Fe has achieved higher performance. However, no one has studied the influence of a small amount of Al ions on the above formula. In this study, the Al3+ ion substituted M-type Sr0.7La0.3Fe11.75ￚxAlxCo0.25O19 (0 ​≤ ​x ​≤ ​0.12) hexagonal ferrites were synthesized by solid state reaction. The crystalline structure was investigated by using X-ray diffraction (XRD) and the Rietveld refining method. The morphological of powder and magnetically oriented bulk were observed by scanning electron microscopy (SEM), and magnetic properties were measured by physical property measurement system-vibrating sample magnetometer (PPMS-VSM) techniques. The results show that a single M-type strontium ferrite was obtained with the Aluminum (Al) content (x) from 0 to 0.08, and the impure phase appeared when x was 0.12. The lattice parameters a and c both decreased with the increasing Al3+ content. SEM images indicate the hexagonal platelet-like particles and the size of the magnetic powders about 2–5 ​μm, and the powders are easily arranged in one direction under a magnetic field. The saturation magnetization (Ms) of the hexaferrite decreased with the increase of x from 0 to 0.12, but coercivity (Hc) of the magnetic powders increased with Al3+ content (x) from 0 to 0.12.

Crystal structure and magnetic properties of Ga-Mn cosubstituted M-type strontium ferrite synthesized by sol-gel method

The M-type hexagonal strontium ferrites substituted by Gd-Mn ions were synthesized by the sol-gel self-combustion method. The synthesized samples were researched by X-ray diffraction (XRD), Fourier transform infrared spectroscopy analysis (FT-IR), scanning electric microscopy (SEM), and vibrating sample magnetometer (VSM). The XRD and the FT-IR results show that the pure M-type hexagonal ferrites phase is successfully obtained in the samples with the substitution amount (x) from 0.00 to 0.09 of Gd-Mn. The VSM results show that, as the substitution amount (x) of Gd-Mn increases, the remanent magnetization (Mr) and saturation magnetization (Ms) of the Sr1-xGdxFe12-xMnxO19 gradually increase, and the maximum values of 39.53 emu/g and 23.73 emu/g were obtained when x = 0.09. When x continues to increase, Mr and Ms decrease slightly, but they are still higher compared with those of the unsubstituted one. The coercivity (Hc) of the samples after doping is much higher than the coercivity of the pure sample, but as the substitution amount x increases, the coercivity first increases and then decreases, while the maximum value of Hc is 6738 Oe at x = 0.06.

Effect of Zn2+-Sn4+ co-substitution on structural and magnetic properties of SrFe12-2xZnxSnxO19 (x = 0–2) M-type strontium ferrite

We studied the structure and magnetic properties of Zn2+-Sn4+ co-substituted M-type strontium ferrite by X-ray diffraction (XRD), Fourier transformer infrared (FT-IR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and superconducting quantum interference device magnetometer (SQUID-VSM). The lattice constants a and c increase monotonically with increasing substitution x, which is primarily attributed to the fact that the ionic radii of Zn2+ and Sn4+ are larger than those of Fe3+. The room temperature magnetic measurement results indicate that the saturation magnetization (Ms) can reach the maximum value Ms = 77 emu/g when x = 0.25, originating from the occupation of Zn2+ and Sn4+ in the spin-down 4f1 and 4f2 sites, respectively. Next, when x ≥ 0.5, the nonmagnetic Zn2+ and Sn4+ weaken the superexchange interaction, resulting in a monotonic decrease in saturation magnetization and coercivity. The sample with x = 0.25 has the optimum magnetic properties of Ms = 77 emu/g, Mr = 35 emu/g and Hc = 2203 Oe, and it is a promising candidate for high-density magnetic recording materials.