Hexagonal Strontium Ferrite Research Articles

Hexagonal strontium ferrite: cationic dye adsorption and antibacterial activity

ABSTRACTHexagonal strontium ferrite (SrFe12O19) powder was synthesized using sonochemical method and characterized. SrFe12O19 was used to adsorb malachite green (MG), a cationic dye, at various physical parameters and investigated against antibacterial activity. The experimental data for the isotherm kinetics followed the Langmuir isotherm model. The synthesized SrFe12O19 powder demonstrates an excellent removal ability with a maximum adsorption capacity (qmax) of 227.27 mg/g for MG. From the antibacterial activity, the material is active against both Gram-negative and -positive bacterial strains, Escherichia coli and Micrococcus luteus, respectively.

Structural, dielectric and magnetic properties of Al-Mn substituted nano-sized M-type strontium hexagonal ferrites

Abstract In this research, we investigated the influence of Al-Mn substitution on the structural, dielectric and magnetic properties of M-type strontium hexagonal ferrites nanoparticles with chemical composition Sr1-xAlxFe11.4Mn0.6O19 (x=0.0, 0.1, 0.2), prepared by sol-gel auto-combustion technique and sintered at 950°C for 5 hours. XRD patterns show the formation of crystalline M-type hexagonal ferrites with traces of α -Fe2O3. FTIR gives the idea of the formation of M-type hexagonal ferrites by showing the presence of characteristics peaks at 438.94 cm-1 and 600.17 cm-1. FESEM shows that the sample exhibit platelet-like structure. The dielectric analysis was carried out in the frequency range 1 KHz to 5 MHz and explained on the basis of Koop’s phenomenological theory and Maxwell Wagner theory. The sample without doping exhibits the highest dielectric constant (1410). Low dielectric loss (0.829) was observed in the sample with x=0.1. The magnetic parameters such as coercivity, remnant and saturation magnetization increases with increase in Al-Mn concentration. High value of coercivity (Hc) (4597.58 Oe) was observed in the sample with x=0.2. The material may be useful for high frequency application.

Structural and Magnetic Properties Evolution of Co-Nd Substituted M-type Hexagonal Strontium Ferrites Synthesized by Ball-Milling-Assisted Ceramic Process

M-type hexagonal Sr1−x Co x Nd x Fe12−x O19 (x = 0, 0.08, 0.16, and 0.24) has been synthesized by ball milling, followed by calcination in air. The calcined products have been characterized by x-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra, and vibrating sample magnetometry. XRD and SEM analyses confirm the formation of M-type Sr hexaferrite with platelet-like morphology when Sr1−x Co x Nd x Fe12−x O19 (x = 0, 0.08, 0.16, and 0.24) precursors are calcined at 950°C in air for 2.5 h. Lattice parameters “a” and “c” values of Sr1−x Co x Nd x Fe12−x O19 reflect a very small variation after doping of Nd3+ and Co2+ ions. Average crystallite size of Sr1−x Co x Nd x Fe12−x O19 sample, calcined at 1150°C, decreased obviously after doping of Co2+ and Nd3+ ions. This is because the bond energy of Nd3+-O2− is much larger than that of Sr2+-O2−. Magnetic characterization indicates that all the samples exhibit good magnetic properties. Substitution of Sr2+ and Fe3+ ions by Nd3+ and Co2+ ions can improve the specific saturation magnetizations and remanence of Sr1−x Co x Nd x Fe12−x O19. Sr0.84Co0.16Nd0.16Fe11.84O19, calcined at 1050°C, has the highest specific saturation magnetization value (74.75 ± 0.60 emu/g), remanence (45.15 ± 0.32 emu/g), and magnetic moment (14.34 ± 0.11 μ B); SrFe12O19, calcined at 1150°C, has the highest coercivity value (4037.01 ± 42.39 Oe). These magnetic parameters make this material a promising candidate for applications such as high-density magnetic recording and microwave absorbing materials.

Microwave absorption behavior and electromagnetic properties of Ni-Zr doped La-Sr hexagonal ferrite synthesized by auto-combustion method

Strontium hexagonal ferrites with compositional formula Sr0.85La0.15(NiZr)xFe12-2xO19, where ‘x’ varies from 0.00 to 1.00 in steps of 0.25, were synthesized by auto-combustion method. Structural, magnetic, electromagnetic and microwave absorption properties of synthesized ferrites were studied. The vector network analyzer (VNA) was used to measure complex permittivity (ε′–jε′′) and complex permeability (μ′–jμ′′) in X-band (8–12.4 GHz) and Ku-band (12.4–18 GHz) frequency range. The minimum reflection loss curves were obtained using back metal plate method for analyzing absorption properties of the material. All the synthesized ferrites show maximum absorption in Ku-band for sample thickness in the range of 1.6–1.68 mm. These newly synthesized ferrites have great potential to be used as thin microwave absorber sheets with minimum reflection loss values in the range of –19.69 dB to −27.8 dB and bandwidth in the range of 680 MHz–1.25 GHz.

Magnetic and Structural Properties of SrFe12−xCrxO19 (x = 0, 0.25, 0.5, 0.75, 1) Hexaferrite Powders Obtained by Sol–Gel Auto-Combustion Method

The crystalline structure and magnetic properties of chromium substituted hexagonal strontium ferrite, SrFe12−xCrxO19 (x = 0, 0.25, 0.5, 0.75, 1), nanoparticles have been investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM). These materials were prepared by the chemical sol–gel auto-combustion method. From the structural analysis, it was observed that the non-magnetic phase α-Fe2O3 appears after x ≥ 0.5 and remains to be a hexagonal magnetoplumbite phase for x < 0.5. Various parameters such as lattice constants (a and c) were calculated from the XRD data. The coercively H c initially decreases and then increases with increasing chromium concentration. The saturation magnetization exhibits an increase as the chromium content increases up to (x = 0.25) and then decreases with increase in the Cr content ion from 75.19 to 61.66 emu/g due to the substitution of Fe3+ ions by less magnetic Cr3+ ions. Furthermore, M r continually decreases with increase in the Cr content.

Effect of Y-La-Co substitution on microstructure and magnetic properties of M-type strontium hexagonal ferrites prepared by ceramic method

M-type permanent magnetic ferrites Sr0.95−xY0.05LaxFe11.75Co0.25O19 (x=0.00, 0.10, 0.20, 0.30, 0.40) have been prepared by ceramic process and investigated systematically. The phase compositions were examined by X-ray diffraction, the results showed that the single phase was obtained when x≤0.30. The morphology of the magnets was investigated by scanning electron microscopy (SEM), the micro-morphology of the particles exhibited the uniform plane hexagonal structure with different lanthanum content. Magnetic properties of the sample were measured by a physical property measurement system-vibrating sample magnetometer (PPMS-VSM). The saturation magnetization (Ms) decreases constantly with the increasing of La content (x). However, the coercivity (Hc) increases as the increasing of doping content.

Magnetic property enhancement of cobalt-free M-type strontium hexagonal ferrites by CaCO3 and SiO2 addition

An experiment was performed to investigate whether CaCO3 and SiO2 addition enhances the magnetic properties of cobalt-free M-type Sr ferrites, in which experimental parameters such as additive composition and the CaCO3/SiO2 ratio were changed. The specimens were prepared using conventional ceramic techniques. CaCO3 addition promoted densification and uniform grain growth, resulting in high remanence; however, with the simultaneous addition of CaCO3 and SiO2, coercivity decreased to 3046 Oe in Sr ferrite hard magnets without Co3O4. SiO2 addition suppressed grain growth. The addition of appropriate concentrations of CaCO3 and SiO2 as additives after calcination was shown to be very beneficial for tailoring a dense microstructure with relatively small grains. A CaCO3/SiO2 ratio of approximately 1.8 was found to be optimum, and the magnetic properties of Br = 4.3 kG, iHc = 3.7 kOe, and (BH)max = 4.5 MGOe were obtained for Sr ferrite hard magnets without Co3O4, which are acceptable for motor applications under output power <1 kW.

Microstructure and magnetic properties of M-type strontium hexagonal ferrites with Y-Co substitution

According to the formula Sr0.95Y0.05Fe12−xCoxO19 (x=0.00, 0.08, 0.16, 0.24, 0.32, 0.40), the replacement of Y-Co in M-type strontium hexagonal ferrites have been successfully prepared by ceramic process for the first time. The phase compositions of magnetic powders were examined by X-ray diffraction. The results of XRD showed that the single phase was obtained in magnetic powders with the increase of Co content (x), and α-Fe2O3 occurred when x>0.24. The morphology of the magnets was investigated by scanning electron microscopy (SEM). The micro-morphology of the particles exhibited the uniform plane hexagonal structures of M-type ferrites with different Co content. Magnetic properties of the ferrite magnets were measured by a physical property measurement system-vibrating sample magnetometer (PPMS-VSM). The Ms increases constantly with the increase of Co content. The Hc first increases and then decreases with the increase of Co content, and the value of coercivity (Hc) is up to 3774 Oe when x=0.24.

Morphology control of hexagonal strontium ferrite micro/nano-crystals

In this study, controllable morphology evolution of hexagonal strontium ferrite (SrFe12O19) micro/nano-crystals has been demonstrated. Single phase strontium ferrite platelets with hexagonal morphology were successfully prepared by conventional ceramic process. In the hexagonal crystals, it is revealed that the anisotropic growth rate is changed, with the increasing of ball milling time, from relatively high rate along the &amp;lt;00l&amp;gt; direction (c-axis) to &amp;lt;hk0&amp;gt; direction, leading to the morphology evolution. Moreover, the optimal saturation magnetization (MS) is 69.5 emu/g, which is intensely close to the theoretical value (72 emu/g). This study provides the direct evidence of the enhanced reaction activity induced by high energy ball milling in strontium hexaferrite platelets and the obtained SrFe12O19 particles are promising for the hard magnet application and the magnetoelectric electronics.

Characteristics Improvement of Low-temperature Sintered SrFe 12 O 19 Ferrites in LTCC System Applications

In order to improve the sintering characteristics of the low-temperature sintered M-type hexagonal strontium ferrites (SrFe 12 O 19 ) prepared by a solid phase method, the Bi 2 O 3 additive was used as a sintering aid. The crystal structure, electrical properties, and magnetic properties of the ferrites were investigated. The results show that the single phase structural SrFe 12 O 19 ferrites can be obtained even with a low sintering temperature of 900 °C. The Bi 2 O 3 additive is found to possess a significant effect on the electrical properties and magnetic properties for the ferrites sintered at low temperatures enhancing resistivity ρ , saturation magnetization M s , intrinsic coercivity H ci , and magnetic anisotropy field H a . It is suggested that the low-temperature sintered SrFe 12 O 19 ferrites with ρ of 0.42×10 8 Ω·cm, M s of 285.6 kA·m −1 , H ci of 347.3 kA·m −1 , and H a of 1546.6 kA·m −1 provide an important potential application in nonreciprocal LTCC (low temperature co-fired ceramics) ferrite devices

Correlation Between Structural Features and Microwave Analysis of Substituted Sr-Co2Y Ceramic Nanoparticles

In this study, Y-type strontium hexagonal ferrite (Sr2Co2Fe12o22) and Sr2Co2Fe12−y/2Al y/2o22 (where y = 0.0–3.0 in a step of 0.5) nanoparticles were prepared by a chemical co-precipitation method. Synthesis time and temperature were varied from 1 to 3 h and 800 to 1000 ∘C, respectively. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), vibration sample magnetometer (VSM), and vector network analyzer (VNA) were employed to study the structural, magnetic, and microwave absorption properties of nanoparticles. According to the results, the optimum condition for synthesize of Y-type Sr-hexaferrite was 900 ∘C at 1 h. The FE-SEM results showed that the particle size increases with increasing in the sintering temperature and also the morphology of particles is slowly twisted from a plate like hexagon to a complex polyhedron shapes. The coercivity has declined from 1327 to 153 Oe and saturation magnetization initially declined and then increased after the formation of Y-type Sr-hexaferrite phase. FE-SEM results for substitution samples showed that the particle size increased with an increase in Al 3+ ion. The maximum reflection loss of substituted Sr-hexaferrites reached −30.7 dB at a frequency of 11.3 GHz and a bandwidth of 3.3 GHz (RL >−10 dB). The obtained results shown that the suggested composites can be introduced as electromagnetic wave absorbers at gigahertz frequency range.

Sonochemical assisted synthesis of SrFe12O19 nanoparticles

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe12O19) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900°C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe3+, Fe2+ and Sr2+ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe2O3) at 300°C. At 500°C, the intermediate species is converted to hematite (α-Fe2O3) by a topotactic transition. The final product of strontium hexaferrite (SrFe12O19) is generated at 800°C. The obtained strontium hexaferrite shows a magnetization of 62.3emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60nm.

Width-controlled M-type hexagonal strontium ferrite (SrFe12O19) nanoribbons with high saturation magnetization and superior coercivity synthesized by electrospinning.

Width-controlled M-type hexagonal SrFe12O19 nanoribbons were synthesized for the first time via polyvinylpyrrolidone (PVP) sol assisted electrospinning followed by heat treatment in air, and their chemical composition, microstructure and magnetic performance were investigated. Results demonstrated that as-obtained SrFe12O19 nanoribbons were well-crystallized with high purity. Each nanoribbon was self-assembled by abundant single-domain SrFe12O19 nanoparticles and was consecutive on structure and uniform on width. PVP in the spinning solution played a significant influence on the microstructure features of SrFe12O19 nanoribbons. With PVP concentration increasing, the ribbon-width was increased but the particle-size was reduced, which distributed on a same ribbon were more intensive, and then the ribbon-surface became flat. The room temperature magnetic performance investigation revealed that considerable large saturation magnetization (Ms) and coercivity (Hc) were obtained for all SrFe12O19 nanoribbons, and they increased with the ribbon-width broadening. The highest Ms of 67.9 emu·g−1 and Hc of 7.31 kOe were concurrently acquired for SrFe12O19 nanoribbons with the maximum ribbon-width. Finally, the Stoner-Wohlfarth curling model was suggested to dominate the magnetization reverse of SrFe12O19 nanoribbons. It is deeply expected that this work is capable of opening up a new insights into the architectural design of 1D magnetic materials and their further utilization.

Synthesis of hexagonal BaFe12O19 and SrFe12O19 ferrite ceramics with Multiferroic Properties

The possibility of obtaining by ceramic technology barium and strontium hexagonal ferrites of the M type with multiferroic properties is considered. For the first time, samples of BaFe12O19 and BaFe12O19 with intense multiferroic properties at room temperature are obtained using a modified ceramic technology (particularly clean feedstock, B2O3 additives, sintering in an oxygen atmosphere). A comparison of the characteristics of the obtained multiferroic samples with the characteristics of the classical high-temperature multiferroic BiFeO3 as well as with the characteristics of ferrite ceramics BaFe12O19 and SrFe12O19 obtained by the technology of polymer precursors is performed. A mechanism to explain the properties of multiferroic hexagonal ferrite ceramic samples is proposed; the important practical significance of the results is noted.

Phase transformation of strontium hexagonal ferrite

The phase transformation of strontium hexagonal ferrite (SrFe12O19) to magnetite (Fe3O4) as main phase and strontium carbonate (SrCO3) as secondary phase is reported here. SrFe12O19 powder was obtained by a heat treatment at 250°C under controlled oxygen flow. It was observed that the phase transformation occurred when the SrFe12O19 ferrite was heated up to 625°C in confinement conditions. This transformation took place by a combination of three factors: the presence of stresses in the crystal lattice of SrFe12O19 due to a low synthesis temperature, the reduction of Fe3+ to Fe2+ during the heating up to 625°C, and the similarity of the coordination spheres of the iron atoms present in the S-block of SrFe12O19 and Fe3O4. X-ray diffraction analysis confirmed the existence of strain and crystal deformation in SrFe12O19 and the absence of them in the material after the phase transformation. Dispersive X-ray absorption spectroscopy and Fe57 Mössbauer spectroscopy provided evidences of the reduction of Fe3+ to Fe2+ in the SrFe12O19 crystal.

Synthesis, structural, magnetic and dielectric properties of zirconium copper doped M-type calcium strontium hexaferrites

Zirconium copper substituted calcium strontium hexagonal ferrites with composition Ca0.5Sr0.5Fe12−2xZrxCuxO19 (x=0.0, 0.2, 0.4, 0.6, 0.8) have been synthesized by the chemical co precipitation procedure. These compounds were characterized by X-ray diffraction, thermogravimetry and scanning electron microscopy. Dielectric and magnetic properties of these hexaferrites were also explored. XRD analysis confirmed the single hexagonal phase of all the compounds and the average crystallite size was between 37 and 47nm. The dielectric parameters show relaxation behaviour at higher frequencies. The values of dielectric parameters increase with dopants. In the range of magnetic field studied, the saturation magnetization decreases as the dopant contents increase which may be due to the nonmagnetic character of the substituents. The coercivity of the Zr–Cu doped derivatives of strontium calcium hexaferrites is increased up to x=0.2 and then decreased. The values of coercivity are above 600Oe which make them suitable materials for use in industries in longitudinal magnetic recording media.

Maximum energy product at elevated temperatures for hexagonal strontium ferrite (SrFe12O19) magnet

The electronic structure of hexagonal strontium ferrite (SrFe12O19) was calculated based on the density functional theory (DFT) and generalized gradient approximation (GGA). The GGA+U method was used to improve the description of localized Fe 3d electrons. Three different effective U (Ueff) values of 3.7, 7.0, and 10.3eV were used to calculate three sets of exchange integrals for 21 excited states. We then calculated the temperature dependence of magnetic moments m(T) for the five sublattices (2a, 2b, 12k, 4f1, and 4f2) using the exchange integrals. The m(T) of the five sublattices are inter-related to the nearest neighbors, where the spins are mostly anti-ferromagnetically coupled. The five sublattice m(T) were used to obtain the saturation magnetization Ms(T) of SrFe12O19, which is in good agreement with the experimental values. The temperature dependence of maximum energy product ((BH)max(T)) was calculated using the calculated Ms(T).

Solvothermal Synthesis of Pure SrFe12O19 Hexaferrite Nanoplatelets

Strontium hexagonal ferrite, SrFe12O19, with platelet-like structure was synthesized directly by hydrothermal method without any calcination process. The product was characterized by Scanning electron (SEM), X-ray powder diffraction (XRD), Fouier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometry (VSM) techniques. The optimum Fe/Sr moler atio is identified as 8:1, and the optimum weight of NaOH was 4.0 g for the synthesis of the Flake-like SrFe12O19 nanoparticles. The average crystallite size of the product was calculated as 28±5 nm. The low coercivities of the synthesized platelet crystals indicate soft magnetic behavior, which is a consequence of the large shape anisotropy (the platelet crystals are highly anisotropic). The reduced Ms can be explained by increasing surface area of the platelets.

Microwave and Millimeter Wave Ferromagnetic Absorption of Nanoferrites

Complex dielectric permittivity and magnetic permeability of several commercially available nanoferrites have been studied over a broad microwave and millimeter wave frequency range. Nano-sized barium, strontium, copper, zinc, nickel substituted iron oxide powders with different lattice structures are investigated. A transmission-reflection based in-waveguide technique that employs a vector network analyzer was used to determine the scattering parameters for each sample in two microwave bands (18-40 GHz). A free space quasi-optical spectrometer energized by backward wave oscillators was used to acquire the transmittance spectra in the millimeter wave frequency range (30-120 GHz). Relatively broad and sharp ferromagnetic resonance of hexagonal barium ferrite and strontium ferrite are observed in millimeter wave frequency range. The ferromagnetic resonance peak for nano-sized hexagonal ferrite powder material moves to lower frequencies compared to micro-sized and solid hexagonal ferrites. An X-ray diffraction measurement is performed on these hexagonal ferrites to understand the magnetic behavior and the structure.

Effect of annealing temperature on the structural, photoluminescence and magnetic properties of sol–gel derived Magnetoplumbite-type (M-type) hexagonal strontium ferrite

Magnetoplumbite-type (M-type) hexagonal strontium ferrite particles were synthesized via sol–gel technique employing ethylene glycol as the gel precursor at two different calcination temperatures (800 and 1000 °C). Structural properties were systematically investigated via X-ray diffraction (XRD), field emission scanning electron microscopy, high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA), photoluminescence spectrophotometry and superconducting quantum interference device magnetometer. XRD results showed that the sample synthesized at 1000 °C was of single-phase with a space group of P6 3/mmc and lattice cell parameter values of a=5.882 Å and c=23.048 Å. EDS confirmed the composition of strontium ferrite calcined at 1000 °C being mainly of M-type SrFe 12O 19 with HRTEM micrographs confirming the ferrites exhibiting M-type long range ordering along the c-axis of the crystal structure. The photoluminescence (PL) property of strontium ferrite was examined at excitation wavelengths of 260 and 270 nm with significant PL emission peaks centered at 350 nm being detected. Strontium ferrite annealed at higher temperature (1000 °C) was found to have grown into larger particle size, having higher content of oxygen vacancies and exhibited 83–85% more intense PL. Both the as-prepared strontium ferrites exhibited significant oxygen vacancies defect structures, which were verified via TGA. Higher calcination temperature turned strontium ferrite into a softer ferrite.