Hexagonal Magnetoplumbite Structure Research Articles

An insight into the structural, magnetic and dielectric properties of modified SrFe12-xPbxO19 (x = 0–0.3)

Effect of Pb2+ substitutions on the structural, magnetic and dielectric properties of SrFe12O19 in the form of SrFe12-xPbxO19 (x = 0, 0.1, 0.2 and 0.3) is carried out. All the samples crystalize in hexagonal magneto-plumbite structure with P63/mmc symmetry. An irregular but randomly distributed particles with average particle size increased from 0.791 μm to 1.131 μm due to substitutions. A characteristics Hopkinson peak is observed just below the transition temperature, may be stems from the superparamagnetic relaxations. The isothermal magnetization depicts an increase in coercivity (Hc) and decrease in saturation magnetization (Ms) due to Pb substitutions, which is further explained in the framework of site symmetry of the Fe and its multiple valence states. Mossbauer study reflects that, Fe3+/ Fe2+ present in the systems are associated with different electric environment. Furthermore, the shifting of dielectric transition by 50 °C upon substitutions is associated to dipole formation in presence of lone pair of Pb2+. A relaxor type of behavior is acquired by the system with a non-Debye type of relaxation is explained on the basis of complexity of the dipoles associated with each crystallographic sites.

Conduction mechanism and magnetic behavior of Cu doped barium hexaferrite ceramics

M-type barium hexaferrite ceramics (BaM) are important materials owing to their tremendous applications and useful properties. However magnetic and electrical properties of Cu substituted BaM haven’t been studied yet. In the present study, Cu doped BaM samples having chemical formula BaFe12−xCuxO19 (where x = 0, 0.1, 0.3 and 0.5) were synthesized by conventional solid state mixed oxide route. X-ray diffraction and Fourier transform infrared spectroscopy confirmed the formation of hexagonal magnetoplumbite structure with space group P63/mmc as the major phase in all the samples. Scanning electron microscopy revealed the dense structure of undoped and doped samples with platelet-like morphology. Vibrating sample magnetometry showed a large decrease in the coercivity of BaM without the loss of saturation magnetization by the addition of Cu. Magnetic measurement at cryogenic temperature (25 K) revealed that Cu doped sample showed less variation in magnetic properties on decreasing the temperature as compared to undoped BaM samples. Room temperature dielectric studies showed that addition of Cu caused a decrease in dielectric loss however it increased at higher substitution level i.e. x = 0.5. High temperature conductivity studies revealed that single-ionized oxygen vacancies are responsible for conduction in Cu doped BaM.

A study on the extent of exchange coupling between (Ba0.5Sr0.5Fe12O19)1−x(CoFe2O4)x magnetic nanocomposites synthesized by solgel combustion method

One step citrate gel combustion method followed by high temperature annealing was employed for preparing (Ba0.5Sr0.5Fe12O19)1−x(CoFe2O4)x (x=0.1, 0.2, and 0.3) composite ferrite powders. The powders were subjected to annealing at 800°C in order to decisively study the phase evolution of the combined hard and soft ferrites. Thermogravitry (TGA)/differential scanning calorimetry (DSC) analysis exhibited three stages of decomposition in the precursor gels combined with an exothermic peak at 210°C. X-ray diffraction (XRD) analysis confirmed that the diffraction peaks were perfectly indexed to the hexagonal magnetoplumbite structure of Ba0.5Sr0.5Fe12O19 and the cubic spinel structure of CoFe2O4. Fourier transform infrared spectroscopy (FT-IR) analysis for the samples showed a Co–O stretching vibration accompanied with Co–O–Co or Fe–O–Fe bands at 1220cm−1. The morphology of the samples were examined by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The crystallinity of a selected sample was evaluated by using the high resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SAED) pattern. It confirmed the presence of planes comprising the hard and soft phases in the synthesized nanocomposites. The magnetic parameters like saturation magnetization MS, remanent magnetization MR, squareness ratio SR, coercivity HC and magnetic moment µB were evaluated using hysteresis by employing vibrating sample magnetometer (VSM). Maximum HC of 4.7kOe and MS of 60.4emu/g were obtained for (Ba0.5Sr0.5Fe12O19)0.9(CoFe2O4)0.1. Switching field distribution curves were analysed by using the demagnetization curve. The exchange coupling between the hard and soft phases were analysed by the dM/dH plots and it indicated the exchange coupling first increased with the increase in the concentration of spinels and then decreased. The possible comparison of exchange coupling between the hard and soft phases has been discussed in detail.

Synthesis and electromagnetic characteristics of Co2Z/Co2Y composite material

The Co2Z/Co2Y composites were synthesized by the solid state sintering method. The phase composition, microstructure and electromagnetic properties of the composites were investigated. The results show that the composites can be prepared by one-step sintering without any other impurity phases in the composites and all the grains show similar microstructure and surface morphology with typical hexagonal magnetoplumbite structure. The electromagnetic properties of the composites reach the best at the 0.5Co2Z/0.5Co2Y sample and the largest absorbing value of an optimal RL of −41.5dB can be obtained at 8.5GHz at a thickness of 3mm.

Effect of carbon and sintering temperature on the structural and magnetic properties of SrFe12O19 nanoparticles

SrFe12O19 magnetic nanoparticles with hexagonal magnetoplumbite structure were synthesized by a modified polyacrylamide gel route and characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectrophotometer, and vibrating sample magnetometer. To obtain large squareness ratio of SrFe12O19, a certain amount of carbon particles were introduced to the precursor solution. X-ray diffraction patterns showed that the carbon and sintering temperature accelerated hexagonal SrFe12O19 phase formation and not changed the hexagonal magnetoplumbite structure. The phase transformation process is closely correlated not only to the sintering temperature but also to the addition carbon particles. In the Fourier transform infrared spectra of SrFe12O19 sample, three obvious absorption peaks at 600, 550 and 439 cm−1 were observed. The carbon introducing to SrFe12O19 precursor solution improved the surface morphology and enhanced the squareness ratio value. The coercivity and squareness ratio of the hexagonal SrFe12O19 are closely correlated not only to the crystallite size but also to the dispersion of nanoparticles of SrFe12O19 sample.

The structure, morphology and magnetic properties of Sr-ferrite powder prepared by the molten-salt method

Sub-micrometre high-performance Sr-ferrite powder was prepared by a molten-salt method using Na2SO4 as the fluxing agent. In the reaction process, a mixture of superfine powder was pre-sintered at 1150 °C for 3 h and then annealed at 850 °C for 2 h. The as-obtained Sr-ferrite powder is SrFe12O19 with a hexagonal magnetoplumbite structure. We observe that with raising the pre-sintering temperature as well as increasing the annealing temperature and time, there is an enlargement of particle size. We regulated the reaction parameters to optimize the magnetic properties of the Sr-ferrite powder. The structure with the best magnetic properties is quasi-cubic in shape and relatively uniform in size, showing a coercivity of 471.89 kA m−1, a saturation magnetization of 91.51 µWb m kg−1, a remanence ratio of 0.50 and a maximum magnetic energy product of 7.89 kJ m−3. We then studied the effects of particle size, demagnetization factor and magnetocrystalline anisotropy on coercivity. Compared with the conventional ceramic process, the one presented here is more convenient and economical for the production of homogeneous hexagonal ferrite powders of high magnetic performance.

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 (Tc = 495 °C of pH 9 sample) in comparison to its bulk counterpart Tc = 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.

Preparation and magnetic properties of lanthanum- and cobalt-codoped M-type strontium ferrite nanofibres

(x = 0.12) nanofibres have been successfully prepared by sol-gel method, electrospinning and subsequent heat treatment. The prepared nanofibres were characterised via X-ray diffraction (XRD), transmission electron micrograph (TEM) and superconducting quantum interference device (SQUID). The XRD revealed that the crystal structure of samples was hexagonal magnetoplumbite structure at calcination temperature from 900 °C to 1100 °C. The TEM showed that the ferrite nanofibres had a smooth morphology and a bamboo joint structure, and the diameter of nanofibres increased with the increase of sintering temperature. The SQUID revealed that there were some intriguing changes in magnetic properties with the variation of sintering temperature or altering calcination time, and the optimised magnetic property of samples was Ms 70.76 emu/g, Mr 36.35 emu/g and Hc 6.26 kOe at 950 °C for 2 h, the corresponding grain size was 39.30 nm. Meanwhile, the nanofibres display more significant improvements in the magnetic properties than the nanoparticles obtained by the sol-gel process, which was probably due to the anisotropic morphology and the cylindrical magnetic domain of ferrite nanofibres.

Optimizing the methods of synthesis for barium hexagonal ferrite—An experimental and theoretical study

Abstract M-type barium hexaferrite (BaM) is a hard ferrite, crystallizing in space group P6 3 /mmc possessing a hexagonal magneto-plumbite structure, which consists of alternate hexagonal and spinel blocks. The structure of BaM is thus related to those of garnet and spinel ferrite. However the material has proved difficult to synthesize. By taking into account the presence of the spinel block in barium hexagonal ferrite, highly efficient new synthetic methods were devised with routes significantly different from existing ones. These successful variations in synthetic methods have been derived by taking into account a detailed investigation of the structural features of barium hexagonal ferrite and the least change principle whereby configuration changes are kept to a minimum. Thus considering the relevant mechanisms has helped to improve the synthesis efficiencies for both hydrothermal and co-precipitation methods by choosing conditions that invoke the formation of the cubic block or the less stable Fe 3 O 4 . The role played by BaFe 2 O 4 in the synthesis is also discussed. The distribution of iron from reactants or intermediates among different sites was also successfully explained. The proposed mechanisms are based on the principle that the cubic block must be self-assembled to form the final product. Thus, it is believed that these formulated mechanisms should be helpful in designing experiments to obtain a deeper understanding of the synthesis process and to investigate the substitution of magnetic ions with doping ions.

Magnetic properties of La–Co substituted barium ferrite thin films with large magnetic anisotropy

Abstract Barium ferrite thin films with lanthanum ions and cobalt ions substituted for barium ions and iron ions have been prepared by conventional diode sputtering method. The hexagonal magnetoplumbite structure was formed by an annealing at 800°C or above. La–Co-substituted barium ferrite thin films had large magnetic anisotropy compared with non-substituted barium ferrite thin films. Moreover, an attempt was also made to reduce the film thickness of La–Co-substituted barium ferrite thin films, in order to utilize them as perpendicular magnetic recording media.

Synthesis, transport and magnetic study of CaLaCr 11O 19

The substitution of chromium and lanthanum in the M-type calcium ferrites has been investigated with its effect on the electrical and magnetic properties. The sample CaLaCr 11O 19 was characterized by X-ray diffraction. It was found to have a hexagonal magnetoplumbite structure. The variation of inverse molar susceptibility and conductivity have been measured from room temperature to 800 K. The thermoelectric studies were carried out for finding out the type of charge carrier.

Magnetic characterization of substituted calcium hexafemte

Three samples of calcium hexafemte with Al, Co and Cr substitutions have been synthesized and characterized. Samples with general formula CaMe 3Fe 9O 19 (Me = Al, Co or Cr) are found to have hexagonal magnetoplumbite structure. Though no structural transformations have been observed on different substitutions, magnetic studies revealed a great difference in these ferrites. Variations of inverse molar susceptibility and conductivity have been measured at various temperatures.

Structural and magnetic properties of CaAl4Fe8O19

A new compound, CaAl4Fe8O19, was synthesized for the first time and characterized by X-ray diffraction. It was found to have a hexagonal magnetoplumbite structure with lattice parametersa=5·83 Å andc=22·14 Å. The electrical studies showed that the compound was a semiconductor with energy of activationq=0·86 eV. The magnetic susceptibility was studied in the temperature range 300 K to 850 K, in which the compound was paramagnetic with a Curie molar constant of 31·03.

Sr系フェライトについて（第1報）

X ray powder photographs have been taken of samples of the system SrO-Fe2O3 and it is found that at least three phases are present in this system; one of them is of the hexagonal magnetoplumbite structure, which is strongly magnetic. Another one, corresponding to the composition of 0.7 SrO 0.3Fe2O3 is cubic, with its lattice constant equal to 3.86×n Å, where n is an integer. This is not ferromagnetic at room temperature. The last phase, whose crystallographic symmetry is unknown, occurs at the composition SrOFe2O3. The observed ferromagnetism seems to originate exclusively from the magnetoplumbite structure.