Magneto-Structural Characterization of Strontium Substituted Lead Hexaferrite

In this work, the magnetic and structural properties of the system Pb_1?x Sr _x Fe₁₂O₁₉ (x=0.1,0.3,0.5,0.7 and 0.9) are reported. The samples were prepared by the traditional ceramic method. All the compounds are isostructural with the strontium hexaferrite (SrFe₁₂O₁₉). X-ray powder diffraction was used to carry out the quantitative analysis of phases and to determinate the crystallographic parameters. It was found that the compound consists of only one phase and that the coercivity, remanence and saturation increased with the strontium content. The initial susceptibility was also obtained and results are discussed in terms of the magnetization mechanisms produced by the effect of the substitution on the hexaferrite. Furthermore, Néel temperature measurements indicate a strengthening of the exchange interactions with increasing strontium content.     

A novel approach for synthesis of M-type hexaferrites nanopowders via the co-precipitation method

M-type hexaferrites; barium hexaferrite BaFe₁₂O₁₉ and strontium hexaferrite SrFe₁₂O₁₉ powders have been successfully prepared via the co-precipitation method using 5 M sodium carbonate solution as alkali. Effects of the molar ratio and the annealing temperature on the crystal structure, crystallite size, microstructure and the magnetic properties of the produced powders were systematically studied. The results indicated that a single phase of barium hexaferrite was obtained at Fe³⁺/Ba²⁺ molar ratio 12 annealed at 800–1,200 °C for 2 h whereas the orthorhombic barium iron oxide BaFe₂O₄ phase was formed as a impurity phase with barium M-type ferrite at Fe³⁺/Ba²⁺ molar ratio 8. On the other hand, a single phase of strontium hexaferrite was produced with the Fe³⁺/Sr²⁺ molar ratio to 12 at the different annealing temperatures from 800 to 1,200 °C for 2 h whereas the orthorhombic strontium iron oxide Sr₄Fe₆O₁₃ phase was formed as a secondary phase with SrFe₁₂O₁₉ phase at Fe³⁺/Sr²⁺ molar ratio of 9.23. The crystallite sizes of the produced nanopowders were increased with increasing the annealing temperature and the molar ratios. The microstructure of the produced single phase M-type ferrites powders displayed as a hexagonal-platelet like structure. A saturation magnetization (53.8 emu/g) was achieved for the pure barium hexaferrite phase formed at low temperature 800 °C for 2 h. On the other hand, a higher saturation magnetization value (M _s = 85.4 emu/g) was obtained for the strontium hexaferrite powders from the precipitated precursors synthesized at Fe³⁺/Sr²⁺ molar ratio 12 and thermally treated at 1,000 °C for 2 h.     

Study of morphological and magnetic properties of microwave sintered barium strontium hexaferrite

Magnetic materials are important electronic materials that have a wide range of industrial and commercial applications. Barium strontium hexaferrite (Ba_0.5Sr_0.5Fe₁₂O₁₉-BSF) were prepared by a sol–gel method using d-Fructose as fuel and the heat treatment was carried out in a microwave furnace. The effects of the sintering temperature on the morphology, crystalline structure and magnetic properties are studied. Sintering temperature affected the grains in compact samples. The sintered product possessed dense microstructure with clear micro grains and is in consistence with the XRD analysis based on the peak intensity of the (107) plane. Magnetic measurement shows that the barium strontium hexaferrite sample sintered at 1,150?°C has the coercive field of 1,998 Gauss, remnant magnetization of 38.87?emu/g and the saturation magnetization of 53.44?emu/g.     

Preparation of magnetic coatings from strontium hexaferrite on tin and cardboard by cold rolling

A finely dispersed powder of strontium hexaferrite doped with aluminum of the composition SrFe_12?x Al _x O₁₉ with an aluminum content x = 0.6 ± 0.1 is prepared through crystallization of oxide glasses. The powder is characterized by a saturation magnetization of 60.2 A m²/kg and a coercive force of 550 kA/m. The hexaferrite particles predominantly have the shape of thick hexagonal platelets with a diameter ranging from 300 to 500 nm and a thickness-to-diameter ratio varying from 0.3 to 0.5. Magnetic coatings on tin and cardboard substrates are produced by cold rolling of strontium hexaferrite powders. It is shown that hexaferrite particles in the magnetic coatings have the preferred orientation of the well-developed facets along the rolling plane, which manifests itself in anisotropy of the magnetic properties of the coatings. The degree of texturing in the strontium hexaferrite coatings on cardboard and tin substrates is equal to 44 and 66%, respectively.     

Hydrothermal Synthesis of SrFe12O19 and Its Characterization

We have synthesized strontium hexaferrite particles in an alkaline medium using a hydrothermal process at 180?°C. Crystalline phase of samples were determined by XRD and spectroscopic, morphological, and magnetic investigation of the sample were FT-IR, SEM, and TG analysis, respectively. XRD analysis revealed few impurity phases in the as-made powder; upon calcinations, the material is converted to desired hexaferrite phase. As synthesized powder exhibits agglomerates with rather smooth facets, in the form of thick platelets. Upon calcination, all these structures were observed to transfer to rod-like structures. The As calcined sample has high specific saturation magnetization (M _s ) values of 65?emu/g that is close to its theoretical value of 74.3?emu/g but the hydrothermally synthesized sample does not. This is in agreement with the observations from XRD analysis where few impurity phases observed in the as-made powder cause a weak magnetic response. Upon calcination, the material is converted to a desired hexaferrite phase with better magnetic properties.     

Effect of Ho3+ substitution on magnetic and microwave absorption properties of Sr(ZnZr)0.5Fe12O19 hexagonal ferrite nanoparticles

Sr_1?x Ho _x (ZnZr)_0.5Fe₁₁O₁₉ (x = 0.03, 0.06 and 0.09) hexaferrite nanocrystallites of average sizes in the range of 46–60 nm are synthesized by the citrate sol–gel method. Crystalline structure, morphology, magnetic properties, and microwave absorption properties of powders were studied via X-ray diffraction, field emission scanning electron microscope vibrating sample magnetometer, and vector network analyzer, respectively. The magnetic properties such as saturation magnetization (M _s ) and coercivity (H _c ) were calculated from hysteresis loops. The XRD patterns show that the main phase is M-type strontium hexaferrite without other impurity phases. Microwave absorption properties of hexaferrite (70 wt%)–acrylic resin (30 wt%) composites were measured by the standing-wave-ratio (SWR) method in the range from 12 to 20 GHz. Results showed that substitution of Ho³⁺ ions for Sr²⁺ ions in Sr(ZnZr)_0.5Fe₁₁O₁₉ resonance frequency moves to higher frequency. For samples with x = 0.03, a minimum reflection loss of ?42 dB was obtained at 16.6 GHz for a layer of 1.7 mm in thickness. It was concluded that the prepared composites could be good candidates for electromagnetic compatibility and other practical applications at high frequency.     

Synthesis and Characterization of Bioceramic Calcium Phosphates by Rapid Combustion Synthesis

Calcium hydroxyapatite(Ca10(PO4)6(OH)2) has been synthesized in short duration by rapid solution combustion by employing different fuels.Calcium nitrate was taken as source of calcium and diammonium hydrogen phosphate served as the source of phosphate ions.Citric acid,tartaric acid,sucrose,glycine and urea were used as the fuels and nitrate ions and nitric acid were used as oxidizers.The influence of fuels on the morphology of the phase formed was studied.Results of the studies by powder X-ray diffraction a...     

Magnetic properties of Ni–Co doped barium strontium hexaferrite

A series of Ni–Co substituted barium strontium hexaferrite materials, Ba_0.5Sr_0.5Ni _x Co _x Fe_12–2x O₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8 mol%) was synthesized by the sol–gel method. X-ray diffraction analysis has shown that the Ni–Co substitutions maintain in a single hexagonal magnetoplumbite phase. The room temperature magnetic properties and the cation site preferences of Ni–Co substituted ferrite were investigated by VSM. Substitutions led to decrease in coercivity while saturation magnetization remains the almost same. It indicates that the saturation magnetization (52.81–59.8 Am²/kg) and coercivity (69.83–804.97 Oe) of barium strontium hexaferrite samples can be varied over a very wide range by an appropriate amount of Ni–Co doping contents.     

Effect of fuel characteristics on synthesis of calcium hydroxyapatite by solution combustion route

The effect of fuel characteristics on the processing of nano sized calcium hydroxyapatite (HA) fine powders by the solution combustion technique is reported. Urea, glycine and glucose were used as fuels in this study. By using different combinations of urea and glycine fuels and occasional addition of small amounts of highly water-soluble glucose, the flame temperature (T _f) of the process as well as product characteristics could be controlled easily. The powders obtained by this modified solution combustion technique were characterized by XRD, FTIR spectroscopy, SEM, FESEM-EDX, particle size analyser (PSD) and specific surface area (SSA) measurements. The particle size of phase pure HA powder was found to be <20 nm in this investigation. The effects of glucose addition with stoichiometric (μ = 1) and fuel excess (μ > 1) urea and glycine precursor batches were investigated separately.     

Enhancement of hard magnetic properties of BaFe12O19 nanoparticles

Barium hexaferrite nano particles are prepared through glycine assisted sol–gel auto combustion method with a minimal glycine to nitrate ratio and the pH values of 4, 6 and 9. X-ray diffraction patterns reveal the formation of hexagonal magneto-plumbite structure of BaFe₁₂O₁₉ with a weak intensity of secondary phase in the case of pH 4 and pH 6 samples. Interestingly disappearance of secondary phase at pH 9 sample is noticeable feature. Scanning electron microscope micrographs of the samples show the formation of characteristic hexagonal shape of barium hexaferrite. Constituent elements and chemical composition are analyzed using energy dispersive X-ray spectrum. Fourier Transform Infra Red and Raman spectra show the different metal–oxygen stretching vibration modes corresponding to octahedral, tetrahedral and trigonal bipyramidal sites of BaFe₁₂O₁₉. Magnetization studies show increase in saturation magnetization, squareness ratio, coercivity values on increasing the pH of the solution. 10 % enhancement of Curie temperature is observed (T_c = 495 °C of pH 9 sample) in comparison to its bulk counterpart T_c = 450 °C reported earlier. Enhancement of magnetic properties is achieved by optimizing pH and suitable choice of post annealing temperature during synthesis of nanoparticles of barium hexaferrite.     

Oxidation of SrFe12O19-based solid solutions with double heterovalent cation substitution

The effect of oxidizing annealing on the phase composition, microstructure, and magnetic properties of solid solutions based on Pb-containing strontium M hexaferrite is studied. The solid solutions prepared by different methods (ceramic route and glycol-citrate sol-gel process) are shown to differ in composition. Oxidizing annealing (air, 500–700°C) of single-phase materials leads to the formation of nanometer-sized (10–20 nm) equiaxed precipitates on some of the faces of the (initially smooth) hexaferrite grains. In some cases, such precipitates form chains running over the entire surface of the hexaferrite grain. Some of the annealed solid solutions contain a second phase, which has not been identified. Annealing slightly increases the coercive force of the solid solutions (by 2 to 25%, depending on their composition), which may be due to oxidation-induced second-phase precipitation or phase segregation of the solid solution within the hexaferrite grains.     

Fabrication,Characterization, and Magnetic Properties of BaAlFe<Subscript>11</Subscript>O<Subscript>19</Subscript> Particles Via Auto Combustion Method

Al-substituted barium hexaferrite particles have been successfully synthesized via sol-gel auto combustion method in the presence of citric acid as fuel. Thermal decomposition, phase evolution, and the microstructure of products were characterized by DTA/TG, XRD, and SEM. Magnetic measurements were carried out on a VSM. To investigate the effects of citric acid to metal nitrate (CA/MN) molar ratios and combustion temperatures on the morphology, phase structure, and magnetic properties of products and finding the optimal condition, several experiments were carried out. The results revealed that the formation temperature, crystallite size as well as magnetic properties are significantly influenced by these parameters. A saturation magnetization of 56.96 emu/g and a coercivity of 7279 Oe were obtained in BaAlFe₁₁O₁₉ powders with CA/MN = 1.0. High Ms and Hc values make them particularly suitable for hard magnetic applications.     

Heat treatment of strontium hexaferrite powder in nitrogen,hydrogen and carbon atmospheres: a novel method of changing the magnetic properties

Strontium hexaferrite powder has been treated in nitrogen, hydrogen and carbon atmospheres. The results show that the phase composition and morphology, and hence, the magnetic properties of the strontium hexaferrite are affected significantly by these gas/vapour treatments. Generally, the coercivity decreased to below 0.8 kOe (regardless of the initial coercivity) and the magnetization at 14 kOe increased significantly, when strontium hexaferrite powder had been treated in a nitrogen, hydrogen or carbon atmosphere. However, it was found that a post-gas treatment of calcination in air, under appropriate conditions, resulted in a recovery of the hexaferrite structure (i.e. it is a reversible reaction). However, the particle/grain sizes of the calcined samples were significantly smaller than those of the non-treated samples, and it is believed that they were single domain particles/grains. In some cases, the coercivity increased by about 400%. The magnetization at 14 kOe and the remanence were either not affected or sometimes increased; magnetic measurements indicated a preferred orientation of the grains.     

Controlled synthesis and photocatalytic activities of barium hexaferrite nanoparticles and examine decolorization methyl orange on liver of rats

The controlled morphological of magnetic nanoparticles have gained great importance in a wide variety of applications due to their promising physico-chemical properties. Therefore, in this study, barium hexaferrite (BaFe₁₂O₁₉) nanoparticles were prepared with the simplest and most efficient chemical route, the two-step sol–gel method, in the presence of seven different and widely used surfactants. The aim of this research is to investigate the influence of the different surfactants on the morphology and particle size of the BaFe₁₂O₁₉ nanoparticles; therefore, different techniques were employed in order to elucidate the composition and structure of the BaFe₁₂O₁₉ nanoparticles such as XRD, SEM, FT-IR, and EDX. The magnetic properties were investigated by measuring the hysteresis loops. In order to investigate the role of BaFe₁₂O₁₉ nanoparticles as the photocatalysts, decolorization of methyl orange under ultraviolet light irradiation was also evaluated. In addition, the purity of decolorized water was examined by investigating its effect on the health condition of liver of rats.     

Role of fuels on intrinsic and extrinsic properties of CoFe2O4 synthesized by combustion method

We have investigated the role of two different fuels viz. glycine and hexamethylenetetramine (HMT) on the electric and magnetic properties of cobalt ferrite synthesized by combustion method. X-ray diffraction study confirms the proper phase formation and spinel structure. Scanning electron microscope study of S₁ (sample prepared by HMT) shows the porous microstructure while that of S₂ (sample prepared by glycine) shows the dense microstructure. The DC resistivity of S₁ is found to be larger than S₂. The dielectric properties of S₁ and S₂ reveal the usual dielectric dispersion nature. The static contact angle measurement reveals the superhydrophobic and hydrophobic nature for S₁ and S₂ respectively.     

Effect of citric acid content on the structural and magnetic properties of SrFe12O19 thin films

Strontium hexaferrite SrFe₁₂O₁₉ thin films have been synthesized on the Si (100) substrate using spin coating sol-gel process. The influence of different citric acid to metal ions (CA/MN) molar ratios of 0.5, 1 and 1.5 on the formation of SrFe₁₂O₁₉ was investigated. Fourier transform infrared analysis and theoretical calculations were conducted to determine and help control the concentration of metal citrates in solution precursors. X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer techniques were also applied to evaluate the composition, microstructure, crystallite size and magnetic properties of the SrFe₁₂O₁₉ thin films. The results showed that single phase strontium hexaferrite thin films with optimum physical properties can be obtained from the solution with the CA/MN molar ratio of 1 after calcination at 800 °C. The SrFe₁₂O₁₉ thin films synthesized with the CA/MN molar ratio of 1 exhibited crystallite size of 42 nm and isotropically magnetic properties of M_s = 267.5 kA/m (at 795.8 kA/m), M_r = 134 kA/m, and H_c = 341.4 kA/m.     

Effect of fuel type on microstructure and electrical property of combustion synthesized nanocrystalline scandia stabilized zirconia

Nanocrystalline 10 mol% scandia stabilized zirconia (10ScSZ) powders were prepared by combustion synthesis using three different types of fuels (urea, glycine and citric acid). The influence of nature of fuel on phase formation, particle size and morphological characteristics was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of fuel type on electrical conductivity was also evaluated. The 10ScSZ prepared by urea and glycine was fully crystalline whereas citric acid resulted in amorphous form. The powder turned crystalline on calcination at 800 °C. Urea resulted in highly agglomerated powder whereas porous and loose agglomerates were formed with glycine and citric acid as fuels. The powder processed with urea showed higher crystallite size compared to powders processed with glycine and citric acid. The ScSZ electrolyte pellet processed with glycine and citric acid exhibited better conductivity and lower activation energy compared to the electrolyte processed with urea.     

Synthesis and characterization of SrFe12O19 nanoparticles produced by a low-temperature solid-state reaction method

Ultra-fine nanoparticles of strontium hexaferrite, SrFe₁₂O₁₉, have been synthesized by low-temperature solid-state reaction method without ball-milling process. The effects of the preparing conditions of samples such as calcination temperature, Fe³⁺/Sr² and Na¹⁺/Sr²⁺ mole ratio on the phase composition, particle size and shape and magnetic properties of the calcined samples have been investigated by differential thermal analysis, X-ray diffraction, field emission scanning electronic microscopy, and vibrating sample magnetometery. The X-ray diffraction patterns showed the formation of SrFe₁₂O₁₉ single phase at temperatures as low as 750° C. Fine particles with particle size around 30–100 nm obtained at 750° C with Fe³⁺/Sr² mole ratio of 10. The magnetic measurements and structural analysis showed that particles were single domain and exhibited better magnetic properties than those obtained by the ceramic method.     

Structural and microwave properties of Ag-doped strontium hexaferrite

A series of silver-doped strontium hexaferrite with the chemical formula SrAg_ZFe_12-zO₁₉ (0.0?≤?z?≤?1.0) were synthesized by the Co-precipitation method. The crystal structure, morphology, and properties of microwave absorption with Ag concentration were studied. The structural analysis by XRD revealed that the samples are crystallized with an M-type hexagonal structure. The values of lattice parameters, the volume of the unit cell, and X-ray density are increasing with the increase of Ag doping. The least values of Rietveld refinements have confirmed a good correlation between experimental and calculated data. Hexagonal plate-like morphology was observed in SEM images and the grain size decreases with Ag doping. Microwave properties have been measured by a vector network analyzer. Real and imaginary parts of electrical permittivity dependence with the frequencies in X-band (8–12 GHz) have been studied. The Reflection loss (RL) was investigated for all samples in X-band frequencies. Maximum RL of ? 21.95 dB at 10.0 GHz was observed for the composition of silver, z?=?0.4. Improved RL when compared with the pure sample indicating enhanced impedance matching and attenuation constant hence the material can show maximum energy loss for the incident microwaves. The results so obtained are explained based on composition and microwave phenomena. The present studies have confirmed the nature of microwave absorption for Ag-doped strontium hexaferrite.

     

Microstructural and Magnetic Features of SrFe<Subscript>12</Subscript><Emphasis Type="Italic">O</Emphasis><Subscript>19</Subscript> Materials Synthesized from Different Fuels by Sol-Gel Auto-Combustion Method

The nanocrystalline SrFe₁₂ O ₁₉ materials were prepared by a sol-gel auto-combustion method using different fuels such as citric acid, dextrose, aniline, and hexamine. The combustion product obtained from all the fuels except from that of aniline show a single phase of SrFe₁₂ O ₁₉ materials upon annealing at 1000 ^°C/2 h. The combustion product obtained from aniline as fuel shows SrFe₁₂ O ₁₉ as the main phase with α-Fe₂ O ₃ as impurity. No notable change in lattice parameters is observed due to variation in fuels for SrFe₁₂ O ₁₉ materials. With a little change in the NIR relative reflectance (72–85 %) on fuels, the different SrFe₁₂ O ₁₉ materials display high NIR reflectance in the wavelength range, 1500–2500 nm. The photoluminescence emission spectra of SrFe₁₂ O ₁₉ materials reveal a broad emission peak at ～350 nm which is reminiscent to the Ba-based hexaferrite, BaFe₁₂ O ₁₉. The FESEM images expose quite dissimilar morphology for the various fuels used in the synthesis of SrFe₁₂ O ₁₉ materials. Hysteresis loops for all the nanocrystalline SrFe₁₂ O ₁₉ materials observed under the applied field of ±1.5 T at room temperature exhibit hard ferromagnetic property. The SrFe₁₂ O ₁₉ materials produced from glycine and aniline as fuels exhibit highest and lowest M _s values of 61.3 and 50.5 emu/g, respectively.