Hexagonal Platelet-like Shape Research Articles

The Influence of the Electrodeposition Parameters on the Properties of Mn-Co-Based Nanofilms as Anode Materials for Alkaline Electrolysers.

In this work, the influence of the synthesis conditions on the structure, morphology, and electrocatalytic performance for the oxygen evolution reaction (OER) of Mn-Co-based films is studied. For this purpose, Mn-Co nanofilm is electrochemically synthesised in a one-step process on nickel foam in the presence of metal nitrates without any additives. The possible mechanism of the synthesis is proposed. The morphology and structure of the catalysts are studied by various techniques including scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The analyses show that the as-deposited catalysts consist mainly of oxides/hydroxides and/or (oxy)hydroxides based on Mn2+, Co2+, and Co3+. The alkaline post-treatment of the film results in the formation of Mn-Co (oxy)hydroxides and crystalline Co(OH)2 with a β-phase hexagonal platelet-like shape structure, indicating a layered double hydroxide structure, desirable for the OER. Electrochemical studies show that the catalytic performance of Mn-Co was dependent on the concentration of Mn versus Co in the synthesis solution and on the deposition charge. The optimised Mn-Co/Ni foam is characterised by a specific surface area of 10.5 m2·g−1, a pore volume of 0.0042 cm3·g−1, and high electrochemical stability with an overpotential deviation around 330–340 mV at 10 mA·cm−2geo for 70 h.

Synthesis and characterizations of magnesium and titanium doped M-type barium calcium hexaferrites by a solid state reaction method

Magnesium and titanium co-substituted M-type barium calcium hexaferrites Ba0.5Ca0.5Fe12-2xMgxTixO19 (0.0 ≤ x ≤ 0.5) have been synthesized by a solid state reaction method and characterized by XRD, XPS, FTIR, SEM, SQUID. XRD patterns confirm single phase M-type hexaferrite and various parameters such as lattice constants, cell volume, average grain size, X-ray density and profile parameters have been calculated from XRD data. XPS survey and FTIR spectra confirm that hexagonal crystal structure is completely formed, which are correlate closely with the results of Reitveld refined XRD patterns. SEM images of the magnetic powders confirm the hexagonal platelet-like shape. The apparent irreversibility between the zero-field-cooling (ZFC) and field-cooling (FC) curves is observed below 390 K, and the ZFC magnetization curves display a broad peak at a temperature TM. The results are discussed within the framework of random particle assembly model and associated with the magnetic domain wall motion. The saturation magnetization Ms slightly increases with increasing x up to 0.2 at 300 K, and then decreases for x > 0.2. The first anisotropy constant (K1), magnetic anisotropy field (Ha) and coercivity (Hc) decrease with increasing x. These results are discussed in light of the cationic distributions based on the results of the structural refinements.

Influence of the Eu substitution on the structure and magnetic properties of the Sr-hexaferrites

Europium (Eu)-substituted M-type strontium hexaferrites (SrEuM) have been synthesized successfully by using a solid-state reaction method. The crystal structure, valence state, element distribution and temperature-dependent magnetic properties are investigated systematically. The single-phase polycrystalline form of SrFe12O19 can be obtained until the substitution reached 0.10, as exhibited in XRD patterns. All samples display the hexagonal platelet-like shape, and the morphology becomes increasingly mellow and full with rising Eu substitution. A significant improvement of saturation magnetization (Ms) and intrinsic coercivity (Hc) at ultralow and room temperatures are achieved under the substitution effort. The origin of this behavior is explained fully from the occupancy and spin orbit in the hexagonal structure system. Moreover, the analysis of thermal characteristics indicates a superior performance in quality and thermal stability as reflected in DSC-TGA curves. SrEuM will be widely used in the magnetic field for the advantage of the high Curie temperature (Tc = 734K).

Magnetic and optical properties of Gd-Tl substituted M-type barium hexaferrites synthesized by co-precipitation technique

The substitution of numerous cations into hexagonal ferrite has been extensively used to endow novel properties and functionalities for various applications. In the present work Gd-Tl substituted barium hexaferrites prepared by co-precipitation process, having the composition Ba0.75Cu0.25(GdxTl0.5-x)Fe11.5O19 (x = 0.0, 0.25 and 0.50). The hexaferrite formation during calcination of sample x = 0.25 was confirmed by TGA/DSC which was processed at 1000 °C for 3 h. The analysis of X-ray diffraction depicts the existence of magneto-plumbite structure with the formation of a minor secondary α–Fe2O3 phase x ≤ 0.0 and BaFe2O4 phase x ≤ 0.50. UV–Vis spectra reveal the dropping down behavior in the optical energy band gap from 2.47 eV to 1.74 eV. The grains with hexagonal platelet-like shape having size of 0.415–0.446 μm of magnetic powder nanoparticles (MPs) are observed by SEM images. The energy dispersive spectrometer (EDS) analysis was employed for presence of ferrite elements within a single particle. Hysteresis loops signifies the magnetization (Ms) and remnant magnetization (Mr) first increases up to x = 0.25 then reduces with the substitution (x) increment; contrarily, the coercivity (Hc) exhibited initially decreased with maximum content of Tl at x = 0.0 then increases at x = 0.25 after that it decreases at x = 0.50. Maximum values such as Ms (51.727 emu/g), Mr (28.061 emu/g), and Hc (4.057 kOe) are attained for x = 0.25 at room temperature. The synthesized magnetic nanoparticles are found to be suitable for microwave absorbing materials, permanent magnets, catalyst, high density recording media and optoelectronic devices.

An investigation on microstructural, spectral and magnetic properties of Pr–Cu double-substituted M-type Ba–Sr hexaferrites

This is first report on Pr–Cu double-substituted M-type Ba–Sr hexaferrites with nominal compositions Ba0.3Sr0.7−xPrxFe12.0−xCuxO19 (x = 0.00–0.35) fabricated by the solid-state reaction route. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM) and Hysteresis graph meter were used to characterize the synthesized M-type Ba–Sr hexaferrites. XRD results show that the hexaferrites with x ≤ 0.21 exhibited single M-type phase, while the hexaferrites with x ≥ 0.28 exhibited the M-type phase and impurity phases. FE-SEM images proposed that all particles with hexagonal platelet-like shape were homogeneously dispersed. The remanence (Br) first increased with Pr–Cu content (x) from 0.00 to 0.14, and then decreased when x ≥ 0.14. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first decreased with x from 0.00 to 0.14, and then increased when x ≥ 0.14. Maximum energy product [(BH)max] reached the maximum value at x = 0.14.

Enhanced dielectric and optical properties of nanoscale barium hexaferrites for optoelectronics and high frequency application

M-type barium hexaferrites with chemical composition Ba1–xDyxFe12–yCryO19 (x = 0.0,0.1,0.2, and y = 0.0,0.4,0.5) were synthesized via sol–gel auto-combustion method. The samples were pre-sintered at 400 °C for 3 h and sintered at 950 °C for 5 h. The changes in the structural, dielectric, and optical properties were studied after the substitution of Dy3+ and Cr3+ ions. X-ray diffraction (XRD) analysis confirms the formation of single phase hexaferrites with the absence of secondary phase. FTIR analysis gives an idea of the formation of hexaferrites with the appearance of two peaks at 438 cm–1 and 589 cm–1. The field emission scanning electron micrographs (FESEM) show a combination of crystallites with large shapes close to hexagonal platelet-like shape and others with rice or rod-like shapes, whereas EDX and elemental analysis confirm the stoichiometry of prepared samples. The calculated band gap from UV-vis NIR spectroscopy spectra was found to decreases with increase in Dy3+–Cr3+ substitution. The dielectric properties were explained on the basis of Maxwell–Wagner model. Enhancement of dielectric constant at higher frequencies was observed in all the samples. Low dielectric loss is also observed in all the samples and Cole–Cole plot shows that grain boundary resistance (Rgb) contribute most to the dielectric properties. The prepared samples exhibit properties that could be useful for optoelectronics and high frequency application.

Structural and Magnetic Properties of Sn4+ Doped Strontium Hexaferrites Prepared via Sol–Gel Auto-Combustion Method

Sn–Zn–Co-substituted strontium M-type hexaferrite SrZn x Co x Sn2 x Fe12–4xO19 ( $x =0.0$ , 0.3, 0.5, and 0.7) was synthesized via modified sol–gel auto-combustion method. A microwave device was used to obtain the finest particles and to complete the combustion process. By substitution of tetravalent and divalent cations instead of iron, magnetic and structural properties of M-type hexaferrite were changed. So, the effects of Sn4+, Zn2+, and Co2+ doping on the structure and magnetic characterization of M-type hexaferrite were investigated. The Fourier transform infrared spectroscopy revealed bands at 430 and 590 cm−1, related to the stretching vibrating bonds of Fe–O. The X-ray diffraction analysis showed that all samples prepared were of P63/mmc symmetry and average crystal size of 68 nm. Field emission scanning electron microscopy analysis revealed the hexagonal plateletlike shape of all samples. Vibrating sample magnetometer results showed that by increasing the dopants content, coercivity ( $H_{c}$ ), and saturation magnetization ( $M_{s}$ ) changed drastically. Saturation magnetizations decreased during dopants displacement and then reach to the highest value (65.46 emu/g) at $x = 0.5$ then increasing of dopants to $x = 0.7$ , cause the reduction of $M_{s}$ (56.13 emu/g). Coercivity diminished by dopant substitution and the semi-hard samples were received as an alternative to the hard hexaferrite.

Synthesis and characterizations of Al-Sm substituted Ba-Sr M-type hexagonal ferrite nanoparticles via sol-gel route

In this work, the Al3+-Sm3+ substituted M-type Ba–Sr hexaferrites, having a composition of Ba0.4Sr0.6Al0.4-xSmxFe11.60O19 (BSAMFO; Pure, 0.0 ≤ x ≤ 0.4) were synthesized using the sol-gel technique. To achieve the hexagonal phase, the optimum annealing temperature was measured by the TGA analysis. X-ray diffraction (XRD) was employed to identify the phase of magnetic powders (MPs). The XRD pattern reveals that the MPs with Al3+ and Sm3+ contents (for x ≤ 0.4) represent α-Fe2O3 as a second phase and the MPs (with 0.1 ≤ x ≤ 0.4) show the presence of a small amount of FeSmO3 phases. Fourier transform infrared spectroscopy (FTIR) and XRD examination clearly expose the different band modes in structure, formation and the compositions of the hexagonal structure, whereas scanning electron microscopy (SEM) was employed to examine the morphologies of the MPs. The hexagonal platelet-like shape with size 0.54–1.23 µm of MPs is observed by SEM images. The presence of ferrite elements is confirmed by energy dispersive spectrometer (EDS) analysis. The magnetic characteristics of MPs were analyzed by a physical property measurement system-vibrating sample magnetometer (PPMS-VSM). Results reveal that Al3+-Sm3+ substitutions modify the saturation magnetization (Ms), a remanant magnetization (Mr) and coercivity (Hc). Additionally, the Hc value decreased while Ms and Mr exhibited the monotonic behavior as the function of x.

Preparation of Al3+-Co2+ co-substituted M-type SrCaNd hexaferrites and their controlled magnetic properties

Al3+-Co2+ co-substituted M-type SrCaNd hexaferrites with cation compositions Sr0.5Ca0.2Nd0.3Fe12.0-x(Al0.5Co0.5)xO19 were synthesized using the traditional ceramic process by varying AlCo content (x) (0.0 ≤ x ≤ 0.5). The microstructures, morphologies and ferromagnetic properties of the samples were investigated as a function of AlCo content (x) by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transformer infrared (FT-IR) spectroscopy and Hysteresis graph meter. The X-ray diffraction patterns show that the hexaferrites with AlCo content (x) of 0.0 ≤ x ≤ 0.2) exhibited M-type phase and α-Fe2O3 as impurity phase, while the hexaferrites with AlCo content (x) ≥ 0.3 exhibited the single M-type phase. XRD, along with FT-IR analysis confirmed the formation of M-type hexaferrites and the successful substitution of Al3+ and Co2+ ions in the hexaferrite lattice. The results of FE-SEM images proposed that all the particles with regular hexagonal platelet-like shape were homogeneous dispersed. The remanence (Br) first increased with AlCo content (x) from 0.0 to 0.3, and then decreased when AlCo content (x) ≥ 0.3. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first increased with AlCo content (x) from 0.0 to 0.2, and then decreased with AlCo content (x) from 0.2 to 0.3, and increased when AlCo content (x) ≥ 0.3. Maximum energy product [(BH)max] first increased with AlCo content (x) from 0.0 to 0.2, and then decreased at AlCo content (x) ≥ 0.2. Squareness ratio (Hk/Hcj) decreased with increasing AlCo content (x) from 0.0 to 0.5.

Investigating the influence of Cr-Zn substitution on magnetic and structural properties of M-type SrBaSm hexaferrites Sr0.6Ba0.1Sm0.3Fe12.0-x(Cr0.6Zn0.4)xO19

The Cr-Zn substituted M-type SrBaSm hexaferrites Sr0.6Ba0.1Sm0.3Fe12.0-x(Cr0.6Zn0.4)xO19 (0.00 ≤ x ≤ 0.75) were synthesized by the conventional ceramic route. The crystal structures were identified by X-ray diffraction. XRD analysis showed that the magnetic powders with CrZn content (x) from 0.00 to 0.30 had M-type as major phase and α-Fe2O3 as impurity phase, while the magnetic powders with CrZn content (x) ≥ 0.45 exhibited a single M-type phase. The grain morphology of the magnets was observed by a field emission scanning electron microscopy (FE-SEM). The FE-SEM images show that all grains were distributed homogeneously and had regular hexagonal platelet-like shape. The magnetic properties of the magnets were derived from the demagnetizing curves. The remanence (Br) and maximum energy product [(BH)max] first increased with increasing CrZn content (x) from 0.00 to 0.30, and then decreased when CrZn content (x) ≥ 0.30. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first decreased with increasing CrZn content (x) from 0.00 to 0.30, and then slightly fluctuated and basically remained unchanged when CrZn content (x) ≥ 0.30.

Facile synthesis and structural insight of chloride intercalated Ca/Al layered double hydroxide nanopowders

Chloride intercalated Ca/Al layered double hydroxide (Ca/Al-Cl-LDH) was successfully synthesized by a one pot solvent-free mechanochemistry method. The effects of ion contents (0.1, 0.15, 0.2, 0.25, 0.3, 0.35, and 0.4) on phase compositions and structural features were evaluated by Rietveld analysis. The as-prepared specimens were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The XRD-Rietveld refinement results confirmed that the formation of high crystalline hydrocalumite was varied by incorporation of different ion contents. The characterization results demonstrated that pure hydrocalumite was the only crystalline phase in the midrange, while calcium hydroxide and gibbsite were appeared as additional phases with hydrocalumite at low and high Al substitutions, respectively. Detailed study of this phase behavior and structural trends was also scrutinized. Microscopic observations illustrated the hexagonal platelet-like shape of hydrocalumite powders with an average edge length of 397 nm. The thermal decomposition details of Ca/Al-Cl-LDH were scrutinized and reported. This unique approach offers an optimum ion concentration for the future design of Ca/Al-Cl-LDH framework that can be applied for numerous applications like biomedical and water treatment.

CaCO3-based nano-missile potentiates antigen delivery and cross-presentation

Chloride intercalated Ca/Al layered double hydroxide (Ca/Al-Cl-LDH) was successfully synthesized by a one pot solvent-free mechanochemistry method. The effects of ion contents (0.1, 0.15, 0.2, 0.25, 0.3, 0.35, and 0.4) on phase compositions and structural features were evaluated by Rietveld analysis. The as-prepared specimens were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The XRD-Rietveld refinement results confirmed that the formation of high crystalline hydrocalumite was varied by incorporation of different ion contents. The characterization results demonstrated that pure hydrocalumite was the only crystalline phase in the midrange, while calcium hydroxide and gibbsite were appeared as additional phases with hydrocalumite at low and high Al substitutions, respectively. Detailed study of this phase behavior and structural trends was also scrutinized. Microscopic observations illustrated the hexagonal platelet-like shape of hydrocalumite powders with an average edge length of 397 nm. The thermal decomposition details of Ca/Al-Cl-LDH were scrutinized and reported. This unique approach offers an optimum ion concentration for the future design of Ca/Al-Cl-LDH framework that can be applied for numerous applications like biomedical and water treatment.

Magnetic and microstructural properties of Al substituted M-type Ca–Sr hexaferrites

In the current study, Al substituted M-type Ca–Sr hexaferrites, with composition Ca0.6Sr0.1La0.3Fe12−xAlxO19 (0≤x≤1.4), have been prepared using the conventional ceramic techniques. The phase composition of the magnetic powders was characterized by X-ray diffraction (XRD). The XRD data show that the magnetic powders with Al content (x) from 0 to 0.8 show α-Fe2O3 as a second phase, while the magnetic powders with x from 1.0 to 1.4 consist of pure magnetoplumbite without any other impurity phases. A field emission scanning electron microscopy (FE-SEM) was used to observe the morphologies of the magnetic powders. FE-SEM images of the magnetic powders show the hexagonal platelet-like shape. The magnetic properties of the magnetic powders were measured by a physical property measurement system-vibrating sample magnetometer (PPMS-VSM). The saturation magnetization (Ms) linearly decreases with Al content (x) from 0 to 1.4. While the remanent magnetization (Mr) first increases with Al content (x) from 0 to 0.2 and then decreases when Al content (x)≥0.2. However, the coercivity (Hc) increases with Al content (x) from 0 to 1.4.

Influence of stoichiometry on the phase constitution and magnetic properties of M-type Sr-Ca hexaferrites

M-type Sr-Ca hexaferrites Sr0.7Ca0.3FexO19 with varying Fe/(Sr+Ca) molar ratios in between 9.8 and 12.0 have been synthesized by utilizing a solid state reaction process. X-ray diffraction (XRD) was used to characterize the phase composition of the magnetic powders. From the XRD data, it is found that the magnetic powders with Fe/(Sr+Ca) molar ratios from 9.8 to 11.8 consists of pure magnetoplumbite without any other impurity phases, while the magnetic powder with Fe/(Sr+Ca) molar ratio of 12.0 shows α-Fe2O3 as a second phase. Morphologies of the sintered magnets were observed by a field emission scanning electron microscopy (FE-SEM). FE-SEM images of the sintered magnets showed the hexagonal platelet-like shape. A magnetic properties test instrument was used to measure the magnetic properties of the sintered magnets. The remanence (Br) and maximum energy product [(BH)max] first increase with Fe/(Sr+Ca) molar ratio from 9.8 to 11.4 and then begin to decrease when Fe/(Sr+Ca) molar ratio≥11.4. While the intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first increase with Fe/(Sr+Ca) molar ratio from 9.8 to 11.0 and then decrease when Fe/(Sr+Ca) molar ratio≥11.0. The Hk/Hcj ratio reaches the minimum value at Fe/(Sr+Ca) molar ratio=11.0.

Influence of Nd3+ substitution on physical, electrical and dielectric properties of Ba2Zn2Fe12O22 hexagonal ferrites prepared by sol–gel auto combustion method

A series of single phase Y-type hexagonal ferrites having chemical formula Ba2Zn2Nd x Fe12−x O22 (x = 0–0.1) were prepared by sol–gel technique. The X-ray diffraction patterns showed that the ferrites belong to the family of single phase Y-type hexagonal ferrites. The grain size estimated from electron microscope images confirms the crystalline nature of the investigated samples and well defined hexagonal platelet-like shape is a most suitable shape for applications. The increase in resistivity is attributed to the removal of low energy pathway due to doping cation placement at octahedral site. The enhancement in resistivity makes these materials suitable for multi-layer chip inductors. The dielectric constant decreases due to lowering of dipole moment with substitution. The frequency dependent ac conductivity increases with increase in frequency and decrease with Nd doping. The conductivity mechanism so determined was hopping mechanism.

Structural, electrical and magnetic study of Nd–Ni substituted W-type Hexaferrite

A series of Nd–Ni substituted W-type hexaferrites with composition Sr1−xNdxCo2NiyFe16−yO27 (where x=0.0, 0.025, 0.050, 0.075, 0.1 and y=0.0, 0.25, 0.50, 0.75, 1) has been prepared by the chemical co-precipitation method. The effect of rare earth Nd substitution at strontium site while Ni at iron site on microstructure, electrical and magnetic properties has been investigated. All the XRD patterns of the synthesized materials show single W-type hexagonal phase without any other intermediate phases. SEM images show that the particles are homogeneous and hexagonal platelet-like shape. DC electrical resistivity measurements were carried out in temperature range of 298–673K showing metal-to-semiconductor transition when doped with Nd–Ni. The magnetic properties such as saturation magnetization, remanence, squareness ratio and coercivity were calculated from hysteresis loops and were observed to increase with the increase in Nd–Ni concentration up to a certain substitution level which is beneficial for high density recording media.

Substitution effects of La3+ ions on the structural and magnetic properties of Co2Y hexaferrites synthesized by sol–gel autocombustion method

Y-type hexaferrite Sr2Co2LaxFe12−xO22 (x = 0.0, 0.05, 0.10, 0.15, 0.20) powders have been synthesized using the sol–gel autocombustion method. Differential Scanning Calorimetry, Thermogravimetry, Fourier Transform Infra-Red spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometery were used to investigate the samples. XRD patterns confirm the formation of Y-type hexaferrite phase. SEM patterns show that mostly grains exhibit rod shape and some appear in the form of hexagonal platelet shape. The rod or rice shape hexaferrite may be used in catalysis, information storage, surface enhanced Raman scattering, imaging and sensing. The samples with hexagonal platelet-like shape particles may be suitable as microwave absorbing materials. The energy dispersive X-ray spectroscopy spectrum shows the presence of dissolved reactants Sr, Co, La and Fe. The saturation magnetization (Ms) calculated using the law of approach to saturation decrease with the increasing of lanthanum (La3+) contents. The decrease in ‘Ms’ may be because of magnetic dilution and spin canting and hence reduction in the super-exchange interactions. The retentivity (Mr) and coercivity (Hc) enhance with the increase of La3+ contents. The enhancement in coercivity from 193 to 598.6 Oe may be because of increase in the porosity of samples with the increase of La3+ contents. The coercivity of the synthesized materials is few hundred oersteds (Oe), which may be suitable for security, switching, sensing, high frequency applications and is also favorable for electromagnetic materials.

Effects of divalent ions substitution on the microstructure, magnetic and electromagnetic parameters of Co2W hexagonal ferrites synthesized by sol–gel method

Abstract Divalent (Me) ions substituted W-type hexagonal ferrites with chemical formula Ba0.5Sr0.5Co2−xMexFe16O27 (x = 0, 0.5 and Me = Mn, Mg, Zn, and Ni) were prepared by sol–gel autocombustion method at 1300 °C for 5 h. Thermal and IR spectral studies were carried out by means of differential thermal/thermogravimetric analysis and Fourier transform infrared spectroscopy respectively. The microstructure was investigated by using the powder X-ray diffractometer and the field emission gun scanning electron microscope. The results showed that divalent ions substituted W-type hexagonal ferrites were single phase and appeared as hexagonal platelet-like shape which is better shape for microwave absorption. M–H loops of a selected sample were measured up to maximum applied field of 9T in a temperature range of 4.2–400 K. The values of saturation magnetization were calculated by the law of approach to saturation. The room temperature value of coercivity is found to be a few oersteds which is favorable for EM materials. Based on the results of electromagnetic parameters, reflection losses were calculated which are found to depend on the thickness of the absorber.

Preparation and properties of sol–gel synthesized Mg-substituted Ni2Y hexagonal ferrites

A series of single phased Y-type hexagonal ferrites Sr2Ni2−xMgxFe12O22 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by the sol–gel auto combustion method. The effects on structural, magnetic and electrical properties have been investigated by substituting Mg2+ at Ni2+ sites. The X-ray diffraction (XRD) patterns confirm single phase Y-type hexaferrite and various parameters such as lattice constants, cell volume, X-ray density, bulk density and porosity have been calculated from XRD data. The Fourier transform infrared (FTIR) spectra show the characteristics absorption ferrite peaks of the sintered sample. The microstructure was studied by scanning electron microscopy (SEM). All the ferrites show a hexagonal platelet-like shape which is a most suitable shape for microwave absorption. The dielectric constant followed the Maxwell–Wagner interfacial polarization and relaxation peaks were observed in the dielectric loss properties. The room temperature dc electrical resistivity and activation energy were found to decrease for samples x=0.1, 0.2 and increase for the rest of samples hence making these materials suitable for multilayer chip inductors (MLCIs). A soft magnetic behavior was revealed by M–H loops. Saturation magnetization (Ms), retentivity (Mr), coercivity (Hc) and magnetic moment (nB) were found to decrease as the Mg2+ contents increased.

Effect of different rare-earth elements substitution on microstructure and microwave absorbing properties of Ba0.9RE0.1Co2Fe16O27 (RE=La, Nd, Sm) particles

Rare-earth (RE) ions substituted W-type hexaferrite Ba0.9RE0.1Co2Fe16O27 (RE=La3+, Nd3+, Sm3+) were prepared by solid-state reaction method at 1250°C for 5h. The microstructure was investigated using the powder X-ray diffractometer and the scanning electron microscope. The results showed that rare-earth ions substituted barium ferrite was single phase of W-type, and appeared hexagonal platelet-like shape. The lattice parameters ‘a’ and ‘c’ decreased gradually with the decrease of rare-earth ionic radius. The complex permittivity and complex permeability in the range from 0.5 to 18.0GHz were measured by vector network analyzer. The microwave absorption properties were characterized by tanδ, which was calculated using the formula of tanδ=tanδe+tanδm. Furthermore, the reasons of those phenomenons were discussed using the interfacial polarization, intrinsic electric dipole polarization and ferromagnetic theory.