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.     

Highly aluminium doped barium and strontium ferrite nanoparticles prepared by citrate auto-combustion synthesis

Aluminium doped barium and strontium hexaferrite nanoparticles BaAl_xFe_(12−x)O₁₉ and SrAl_xFe_(12−x)O₁₉ were synthesised via a sol-gel route using citric acid to complex the ions followed by an auto-combustion reaction. This method shows promise for the synthesis of complex ferrite powders with small particle size. It was found that around half of the iron could be substituted for aluminium in the barium ferrite with structure retention, whereas strontium aluminium ferrites could be produced with any aluminium content including total substitution of the iron. All synthesised materials consisted of particles smaller than 1 μm, which is the size of a single magnetic domain, and various doping levels were achieved with the final elemental composition being within the bounds of experimental error. The materials show structural and morphological changes as they move from iron to aluminium ferrites. Such materials may be promising for imaging applications.     

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 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.     

Effect of Cu-Co-Zr Doping on the Properties of Strontium Hexaferrites Synthesized by Sol-Gel Auto-combustion Method

In the present study, we have synthesized tri-substituted strontium hexaferrites SrFe _(12?2x)Cu _x/2Co _x/2Zr _x O ₁₉ (x= 0.0 ?1.0, Δx= 0.2) by sol-gel auto-combustion route. The effect of this triple doping has been studied on the structural, dielectric, and magnetic properties of M-type strontium hexaferrite nanoparticles. The characterization of these materials has been done by XRD, FT-IR, VSM, SEM, EDS, and impedance analyzer. Single-phase formation is confirmed at 800 ^°C. Real permittivity decreases while loss tangent increases with increase in substitution. The observed results propose these prepared ferrites for applications in filters, antennas, isolator, circulators, etc.     

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.     

X-ray diffraction studies on aluminum-substituted barium hexaferrite

Effect of aluminum substitution in barium hexaferrite was studied following the hydrothermal precipitation–calcination techniques. It was attempted to prepare aluminum-substituted barium hexaferrites with compositions BaAl_xFe_12−xO₁₉ having x=2,4, 6, 8 and 10. The precursors were prepared by using stoichiometric amounts of Ba, Al and Fe³⁺ nitrate solutions with urea as the precipitating agent. The hydrothermally prepared precursors were calcined at temperatures in the range of 800–1200 °C. The detailed work carried out on identification of crystalline phases through XRD revealed that, after the hydrothermal treatment, the samples showed barium carbonate, hematite and boehmite as the crystalline phases (except that boehmite was not identified for Ba/Al/Fe ratio as 1:2:10). Irrespective of the Al content, none of the 1000 and 1200 °C calcined samples showed any crystalline phase of Al. The 1200 °C calcined samples showed that Al-substituted barium hexaferrite is formed only with the Ba/Al/Fe atomic ratio of 1:2:10. With increase in the Al content, formation of hexaferrite was not observed. BaCO₃ was found be present even at 1200 °C in all the samples except for the one having Fe/Al ratio 5. The normal decomposition temperature of BaCO₃ is between 950 and 1050 °C. It is difficult to explain the increased stability of BaCO₃, which is perhaps responsible for hindering the formation of aluminum-substituted barium ferrite having Fe/Al ratio ≤2. The Al substitution in barium hexaferrite was confirmed through magnetic measurements.     

Preparation and magnetic properties of Ni–Zr doped barium strontium hexaferrite

M-type Hexaferrites B_0.5Sr_0.5Fe_12−2x Ni _x Zr _x O₁₉ were synthesized and investigated. The XRD patterns show single phase of the magnetoplumbite barium strontium ferrite and no other phases were present. The samples exhibit well defined crystallization; all of them are hexagonal platelet grains. As the substitution level increased from x = 0.2 to 0.8 mol%, the grains are agglomerated and the average diameter increased. This suggests that Ni–Zr substitution increases the grain size, as observed in the FE-SEM micrographs. The results of magnetic measurement revealed that M_s of barium strontium hexaferrite increased when the value of x increased from 0 to 0.4 mol% and then decreased with the increasing Ni–Zr content. The H_c decreases remarkably with increasing Ni and Zr ions content. Hard magnetic material is converted into soft magnetic material when the substitution level is increased from 0.2 to 0.8 mol%. In particular, Ba_0.5Sr_0.5Fe_12−2x Ni _x Zr _x O₁₉ with x = 0.2, 0.4, 0.6, 0.8 mol% has suitable magnetic characteristics with particle size small enough for high-density magnetic recording applications.     

Structural and magnetic properties of Ba0.7Sr0.3Fe12 − 2x Co x Ti x O19 M-type hexaferrites

We have studied the effect of “double” substitution in Ba_0.7Sr_0.3Fe_{12 ? 2x} Co _x Ti _x O₁₉ on the structural and magnetic properties of M-type barium hexaferrite. The basic composition of Ba_{1 ? x} Sr _x Fe₁₂O₁₉ obtained by heat-treating carbonate-hydroxide precipitates has been optimized (x = 0.3). 2Fe³⁺ → Co²⁺ + Ti⁴⁺ substitutions considerably reduce the coercive force (H _c) and increase the magnetization (M _s) relative to Ba_0.7Sr_0.3Fe₁₂ O₁₉.     

Phase formation and magnetic property evolution processes of the hexaferrite with composition BaO⋅0.9Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>⋅5.1Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The phase formation and magnetic property evolution processes of the hexaferrite with composition BaO?0.9Sc₂O₃?5.1Fe₂O₃ have been investigated. Results show that when the calcination temperature is lower than 1000 °C, the spinel phase BaFe₂O₄ and M-type hexaferrite phase BaFe₁₂O₁₉ dominate. The M-type hexaferrite BaFe_12?xSc_xO₁₉ (0?<?x?≤?1.8) appears above 1050 °C and becomes a single phase BaFe_10.2Sc_1.8O₁₉ above 1200 °C. A two-step decrease of both the coercivity and remanence ratio is observed above 1050 °C, which agrees well with the appearance of soft magnetic phase BaFe_12?xSc_xO₁₉ (0?<?x?≤?1.8). The saturation magnetization of the sample increases with calcination temperature until 1100 °C and then decreases. Raman spectra results show that the above magnetic property evolutions can be explained by a temperature dependent incorporation of Sc³⁺ into the lattice sites nearby the magnetic blocks’ interfaces. This weakens the local magnetic exchange interactions between Fe³⁺ and thus leads to a change in the magnetic structure.     

Effect of Fuel on the Synthesis and Properties of Poly(methyl methacrylate) Modified SrFe12O19 Nanoparticles

Nanosized strontium hexaferrite (SrFe₁₂O₁₉) has been synthesized by citrate, urea, oxalic, and glycine precursor via a sol-gel route with poly(methyl methacrylate) (PMMA) as a templating agent. Crystal structure, morphology, and magnetic properties of as-synthesized nanoparticles were characterized by XRD, SEM, FT-IR, and VSM techniques. The formation of strontium hexaferrite and its crystallite size in presence of different fuels were compared. The influence of different fuels was reflected on the phase purity, morphology of the final powders as well as the magnetic properties. Magnetic measurements revealed that samples prepared by citric acid and glycine as fuel have high specific saturation magnetization and moderate coercivity, while urea and oxalic acid fuels resulted in low phase purity, and thus inferior magnetic properties.     

Effect of Barium on the Properties of Lead Hexaferrite

An analysis of the properties of a family based on lead-barium substitution in the M-type hexaferrite is presented. The samples were prepared by the ceramic method according to the general formula Pb _x Ba_1?x Fe₁₂O₁₉. The barium content was varied with x=0.1, 0.3, 0.5, 0.7, and 0.9; no secondary phases were detected in any composition. Rietveld refinement analysis was done in order to determinate crystallographic parameters, content of phases and degree of substitution. The effects of the barium on the morphological and magnetic properties were studied. Iron Mössbauer spectroscopy was used for determining the hyperfine parameters of the iron nucleus and their environment; also, the cationic occupancy was evaluated and the results were checked with X-ray refinement results.     

Synthesis and Magnetic Properties of SrO–Fe2O3–B2O3 Glass-Ceramics

Glasses with nominal compositions of SrFe₁₂O₁₉ + 8SrB₂O₄ (I) and SrFe₁₂O₁₉ + 12Sr₂B₂O₅ (II) are prepared by rapid quenching from the liquid state and are converted to glass-ceramics containing fine magnetic particles of SrFe₁₂O₁₉ by heat treatment between 600 and 950°C. The materials are characterized by x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. The phase transformations accompanying glass crystallization are identified. The glass composition and heat-treatment conditions are shown to influence the aspect ratio of the forming submicron-sized strontium hexaferrite particles. The strongest coercive fields reached in glass-ceramics I and II are 504 and 456 kA/m, respectively.     

Preparation of magnetic glass-ceramics through glass crystallization in the Na2O-SrO-Fe2O3-B2O3 system

Glasses with the nominal compositions SrFe₁₂O₁₉ + nNa₂Sr₂B₄O₉ (n = 4, 6, 8, 10) and SrFe₁₂O₁₉ + 6Na₂Sr₃B₄O₁₀ were prepared via rapid quenching of oxide melts and were then heat-treated between 500 and 800°C in order to produce glass-ceramics containing fine SrFe₁₂O₁₉ particles. The materials were characterized by x-ray diffraction, differential thermal analysis, electron microscopy, and magnetic measurements. The crystallization behavior of the glasses was investigated. The coercivity of the glass-ceramics was shown to increase with heat-treatment temperature, up to 486 kA/m. By dissolving the nonmagnetic matrix of the glass-ceramics with the nominal compositions SrFe₁₂O₁₉ + 6Na₂Sr₃B₄O₁₀ and SrFe₁₂O₁₉ + 4Na₂Sr₂B₄O₉, submicron-sized strontium hexaferrite particles were obtained.     

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.     

Influence of Zn–Nb on the Magnetic Properties of Barium Hexaferrite

In the present study, BaFe_12?2x Zn _x Nb _x O₁₉ (x=0. 2, 0.4, 0.6 and 0.8) hexaferrites were prepared by the sol-gel technique and subsequent thermal treatment. The crystal structure, grain size, and magnetic properties were studied by means of X-ray diffraction (XRD), high-resolution scanning electron microscope (HR-SEM) and vibrating sample magnetometer (VSM). The X-ray diffraction analysis showed that the barium hexaferrite with small substitutions still maintained a hexagonal magneto-plumbite phase. It was found that the mean size of the grains increased with increasing substitution. The saturation magnetization increased slightly with increasing x, which was attributed to different preferential site occupation of Zn–Nb at low and high concentration ranges. The coercivity decreased with increasing x. Structural and magnetic characterizations of these ferrites provide significant information about their reactive physical properties.     

Effect of aluminum substitution on microstructure and magnetic properties of electrospun BaFe12O19 nanofibers

BaFe_12?x Al _x O₁₉ nanofibers (x = 0–2.0) with average diameter 110 nm have been prepared via the electrospinning and subsequent heat treatment at 1100 °C for 2 h. Individual BaFe₁₂O₁₉ nanofibers were composed of numerous nanocrystallites stacking alternatively along the long axis of fiber and the single crystallites on each nanofibers had random orientations. With increasing Al³⁺ ions substitution contents from 0 to 2.0, the diameter and morphology of nanofibers were almost no change. However, the lattice parameters decreased due to Fe³⁺ ions substituted by smaller Al³⁺ ions and the average grain size calculated by the Scherrer’s equation reduced from 47 to 42 nm. The crystallites possessed a hexagonal plate-like shape at x = 0 while they became rod-like with various Al³⁺ ions substitution. The X-ray diffraction patterns show that single-phase barium hexaferrite was formed when Al³⁺ ions substitution contents were less than and equal to 1.0, while other impurity phases were detected when they were more than 1.0. The chemical analysis shows that the element Al was all incorporated into the lattice of BaFe₁₂O₁₉ and evenly distributed throughout the BaFe_12?x Al _x O₁₉ nanofibers. The magnetic testing shows that the saturation magnetization (M _s) decreased obviously from 63.92 to 29.70 A m²/kg, while coercivity (H _c) increased significantly from 288.2 to 740.7 kA/m with increasing Al³⁺ ions substitution.     

Dielectric constant, magnetic permeability and microwave absorption studies of hot-pressed Ba-CoTi hexaferrite composites in X-band

The microwave absorption, complex permittivity and complex permeability studies of hot-pressed hexaferrite composites prepared with Ba(CoTi)_xFe_12-2xO₁₉ (x = 0.0, 0.2, 0.4, 0.8, and 1.0) were made in the frequency range from 8.0 to 12.4 GHz. The hexaferrite composites with x > 0.0 exhibit significant dispersion in the complex permittivity (ε_r′-jε_r″). However the dispersion in complex permeability (μ_r′-jμ_r″) is not significant and is attributed to the shielding effect of polymer matrix over the ferrite crystallites. The reflection loss has been studied as function of frequency, composition and thickness of absorber. A comparison of reflection loss of hot-pressed ferrite composites with that of normal sintered ferrite composites was made and analyzed. A minimum reflection loss of—24.0 dB is obtained at 9.9 GHz for 2.8 mm thick sample of BaCo_0.4Ti_0.4Fe_11.2O₁₉ hot-pressed hexaferrite composite.