M-type Hexaferrite Research Articles

Effects of La-Co Co-Substitution and Magnetic Field Pressing on the Structural and Magnetic Properties of SrM Hexaferrites

We carefully investigated the effects of La-Co co-substitution and magnetic field pressing (MFP) on the structural and magnetic properties of SrM hexaferrites. Samples composed of Sr1−xLaxFe12−xCoxO19 were sintered at 1230 °C for 2 h in air with sintering additives composed of 0.7 wt% CaCO3 and 0.7 wt% SiO2. A single M-type phase was confirmed to exist up to x = 0.3. Rietveld refinement revealed a slight decrease in lattice parameter a and the unit cell volume (Vcell) with an increasing x, while parameter c showed a significant decrease. The saturation magnetization (Ms) values increased from 70.90 to 72.40 emu/g with an increasing x from 0.0 to 0.15 and then decreased to 71.38 emu/g with further increasing of x to 0.3, while the anisotropy field (Ha) increased from 17.7 to 25.9 kOe, leading to a continuous increase in the intrinsic coercivity (Hci), from 3.52 to 5.00 kOe, respectively. Using the MFP process, the c-axis of M-type hexaferrite grains could be effectively aligned to the applied field direction, which significantly affected the microstructures and, thus, magnetic properties of samples. Unlike non-MFP samples, exhibiting a significant increase in the average grain size (davg) but almost unaltered average thickness (tavg) with an increasing x from 0.0 to 0.3, MFP-processed samples exhibited almost unaltered davg values but a continuous decrease in tavg. Consequently, the variation in remanent flux density (Br) versus x followed that of Ms versus x and thus exhibited the highest Br of 4.05 kG for x = 0.15, leading to the highest maximum energy product {(BH)max} of 3.62 MGOe. With an increasing x from 0.0 to 0.3, the Hci values continuously increased from 3.14 to 3.84 kOe mainly due to a continuous increase in Ha, although they were significantly lowered in comparison with those of non-MFP samples because of a large increase in Br for a given composition x. A higher Mr/Ms ratio always resulted in a larger (BH)max in our samples regardless of x. A careful comparison of the microstructures and magnetic properties between MFP and non-MFP samples provided valuable insights into a broad area of permanent magnet optimization.

Structural, Morphological, and γ-ray Attenuation properties of m-type hexaferrite BaFe12O19 doped with V2O5, Ce2O3 and Bi2O3 for Radiation Shielding applications

This paper studies, structurally analyzes, evaluates the morphology, and assesses the gamma-ray and neutron attenuation properties of a composite material composed of M-type hexaferrite BaFe12O19 (BF) doped with three additional compounds: Bi2O3, V2O5, and Ce2O3. X-ray diffraction revealed that the structure of BF can be indexed to a hexagonal structure, BF/Bi2O3 to a tetragonal structure, BF/V2O5 to a cubic structure, and BF/Ce2O3 to a trigonal structure. These results were refined using PROFEX software. The Crystallite size of the nano-powders was determined by X-ray line broadening using the Williamson-Hall method. Morphology evaluations illustrated that HR-TEM images for BF, BF/Bi2O3, BF/V2O5, and BF/Ce2O3 reveal high crystallinity with a polycrystalline nature. Various attenuation measurements, using the FLUKA Monte Carlo code, aimed to determine the efficacy of these dopants into m-type hexaferrite BF as potential materials for radiation shielding applications. Doping with Bi2O3 into hexaferrite BF markedly enhances its attenuation properties, demonstrating superior Linear Attenuation Coefficient (LAC) values across a broad energy spectrum from 0.16 to 10 MeV. The Mass Attenuation Coefficient (MAC) analysis revealed a pivotal energy threshold at 0.3 MeV. Below this energy, BF presented the highest MAC values. Conversely, for energies equal to or greater than 0.3 MeV, BF exhibited the highest MAC values, affirming its superior gamma photon shielding efficacy. The study of the Half Value Layer (Δ0.5) and Mean Free Path (MFP) provided additional evidence of the superior shielding performance of BF/Bi2O3. The Δ0.5 values ranged between 0.128 to 1.240 cm for BF, 0.162 to 1.430 cm for BF/V2O5, 0.163 to 1.390 cm for BF/Ce2O3, and 0.162 to 1.210 cm for BF/Bi2O3, indicating that BF/Bi2O3 requires a thinner layer to halve the gamma-ray intensity, particularly at higher energies. The MFP values further support the improved shielding ability of BF/Bi2O3, with measurements showing that gamma photons travel the shortest distance before interacting with the material, thereby reducing the potential for radiation exposure.

Structural, magnetic, low and high frequency dielectric properties of Al-substituted M-type SrCe hexaferrites synthesized in the presence of tecomastans (yellow bell) leaves extract

This paper represents a study of the effect of Al-substitutions on structural, magnetic, and dielectric properties of Sr0·8Ce0·2Fe12-xAlxO19 (x = 0.00, 0.25, 0.50, 0.75 and 1.00) ferrites synthesized in presence of yellow bell leaves extract. All samples were synthesized using the sol-gel combustion technique with the influence of green synthesis by using leaves of Tecomastans (yellow bell) plant. These samples were preheated at 550 °C for 4 h and finally calcinated at 1150 °C for 6h. These samples were characterized using XRD, FTIR spectroscopy, SEM, VSM, LCR measurements, and VNA measurements. XRD analysis confirm the formation of a magnetoplumbite M-phase (hexagonal) with a minor impurity phase of CeO2 in all samples. Lattice parameters a and c are obtained from rietveld refinement, which are found in the range from 5.859 Å to 5.883 Å, and 22.96 Å to 23.05 Å respectively. FTIR spectra confirm the absence of organic compounds and the presence of an absorption band in the fingerprint region, which are linked to the stretching of the metal-oxygen bond at the octahedral and tetrahedral sites. The surface morphology of these samples is analyzed using SEM images. Grains with hexagonal plate shapes were observed in each sample. The average grain size varies in the range of 0.565 μm–1.455 μm. EDS data confirms the presence of desired elements in the respective sample. VSM analysis shows hard magnetic behavior in all samples. Magnetic parameters were found in the range, Ms: 36.281–43.397 emu/g, Mr: 12.297–19.841 emu/g, Hc: 2.0987–3.814 kOe. In low-frequency (20 Hz-2 MHz) dielectric measurements, the dielectric constant is high at low frequencies, which rapidly falls as frequency increases. Loss tangent curve shows a relaxation peak for each sample above 200 kHz. AC conductivity is very low in the order of 10−5 S/m in plateau region below 2 kHz, which increases as frequency increases. Cole-Cole plot suggests the effect of grain boundary contribution is higher in non-substituted sample compared to Al-substituted samples. In high-frequency (0.2 GHz–20 GHz) measurements, the dielectric constant remains almost constant. These values are found in the range 5–7.5. Low loss tangent of 0–0.16 were observed in every sample in this frequency domain, with AC conductivity of the order of 10−2 S/m.

Study on Morphological and Magnetic Aspects of Lithium Addition in M-type Strontium Hexaferrites

Study on Morphological and Magnetic Aspects of Lithium Addition in M-type Strontium Hexaferrites

Impact of cobalt substitutions on optical, magnetic, dielectric, and structural, properties of BaFe11.6-xAl0.4CoxO19 hexaferrites prepared by Co-precipitation process followed by rapid sonochemical synthesis

The dielectric along with magnetic features of hexaferrites could be remarkably improved by cationic substitutions. Therefore, in the current work we synthesized cobalt substituted BaFe11.6-xAl0.4CoxO19 (0 ≤ x ≤ 1.2) hexaferrites via co-precipitation process followed by rapid sonochemical procedure. Structural analysis showed that, as the concentration of Co increased, the lattice-parameters ‘a’, ‘c’, crystallites-size, and volume increased. The SEM micrographs revealed the uniform and homogeneous distributions of particles in all samples. The two strong absorption bands indicated by FTIR analysis confirm the successful formation of M-type hexaferrites. The decreasing trend of optical band gape with cobalt doping is indicated by UV vis spectroscopy analysis. The dielectric-loss(ε''), dissipation factor, and dielectric-constant(ε′), increased as the content of cobalt is raised. The produced M-type hexaferrite exhibits increased AC electrical conductivity with frequency and doping concentration. Non-Debye-type relaxation is suggested by the cole–cole diagrams (Mʹ vs. Mʹʹ) for prepared samples. As Co concentrations increased, the magnetic moments per formula unit(mB) and saturation magnetization increased up to the optimal doping content of x = 0.9, after that these parameters showing decreasing trend. The magnetic anisotropy constant (K), coercivity (Hc), anisotropy-parameter(B), and anisotropy-field(Ha) were all showing increasing tendency with doping content. The investigations above revealed that Co replaced BaFe11.6-xAl0.4CoxO19 (0≤x ≤ 1.2) hexaferrites will be suitable for use as a permanent magnet, magnetic recording media, and other magnetic applications.

Enhanced dielectric properties of co-substituted M-type Sr-La hexaferrite synthesized by citrate auto-combustion method

In this present research, comparative analysis of dielectric and electrical properties of M−type lanthanum-strontium (La-Sr) hexaferrites substituted with Co-Zr, Mn-Zr and Ni-Zr with chemical formulae: Sr0.85La0.15(CoZr)xFe12-2xO19, Sr0.85La0.15(MnZr)xFe12-2xO19 and Sr0.85La0.15(NiZr)xFe12-2xO19 (where x is 0.00 to 1.00 with ratio of 0.25) respectively have been investigated in 1 kHz to 1 MHz frequency range. The dielectric constant and loss tangent are generally shows decreasing trend with frequency and AC conductivity shows increasing trend with it. Dielectric constant, tangent loss and AC conductivity are increased with increase in substitution of Co-Zr and Mn-Zr doped La-Sr ferrites but shows opposite trend for Ni-Zr doped La-Sr hexaferrites. The higher electron exchange between ferrous cations (Fe2+) and ferric (Fe3+) cations are responsible for the higher polarization in ferrites. These newly synthesized ferrites have great potential for microwave absorbing material and microwave components

Influence of bismuth and cobalt doping on structural, dielectric, and magnetic properties of M-type calcium hexagonal ferrites

M-type hexagonal ferrites have been getting considerable attention owing to their promising application in electronic fields. Though, the growth of nanosized M-type hexagonal ferrites is still a big challenge. Herein the fabrication of M-type hexaferrite with nominal composition Ca1-xBixFe12-xCoxO19 (x=0.00, 0.05, 0.10, 0.15, 0.20) with high quality is reported by the sol-gel auto combustion route. The objective of the study is to improve the structural, spectral, dielectric, and magnetic characteristics of M-type hexagonal ferrite which was achieved through the variation of concentration of Cobalt and Bismuth. X-ray diffraction (XRD) patterns confirmed the single-phase M-type hexagonal structure. The crystallite size of all samples was found to be in the range of 42–49 nm. Other parameters such as lattice parameters a & c, unit cell volume, crystallite size, X-ray density, Bulk density, and porosity were also calculated. The doping contents were found to decrease the bulk and X-ray densities while increasing the porosity. Fourier-transform infrared (FTIR) spectra showed the formation of metal-oxygen stretching vibrations that confirmed the formation of hexagonal ferrites. The scanning electron microscopy (SEM) images revealed a regular platelet hexagonal structure and homogeneously distributed grains were examined. The dielectric constant was high at low frequency and then decreased with increasing frequency, while the dielectric loss was decreased appreciably with doping. The saturation magnetization ranged from 15.51 to 38.27 emu/g, coercivity increased from 207.93 to 1359.69 Oe, and the squareness ratio was found to be in the range of 0.19–0.78. The dielectric and magnetic properties of Ca1-xBixFe12-xCoxO19 (x=0.00, 0.05, 0.10, 0.15, 0.20) with the variation of Co and Bi revealed that these materials are good candidates for modern devices.

Investigation of structural phase stability, modified magnetic spin order and low temperature spin glass-like phase transitions in Sc-doped M-type BaFe12O19 hexaferrite

This work used two approaches of mechanical alloying before high temperature solid state reaction to synthesize BaFe12-xScxO19 (x = 0.5 to 6.0) system. Rietveld refinement of X-ray diffraction patterns showed the formation of extra phases at higher Sc doping, along with the main magnetoplumbite structure. Raman spectroscopy suggested random distribution of Sc ions at the Fe-sites of hexaferrite structure. X-ray photoelectron spectroscopy (XPS) confirmed the +3 charge state at the Fe/Sc-sites. The Fe 3s band suggested dilution of ferromagnetic 3s-3d spin exchange interactions. The neutron diffraction study re-confirmed random occupancy of the non-magnetic Sc3+ ions at Fe3+ sites of the Sc doped Ba hexaferrite system. The transformation of magnetic spin order from collinear to non-collinear state has shown spin glass-like features at low temperature regime in the dc magnetization curves. This is an effect of dilution of Fe–O–Fe ferrimagnetic super exchange interactions and spin frustration in Sc-doped samples.

Functionalization of morphology in optimization of dielectric, electrical/impedance modulus, and relaxation mechanisms of Co-Ni doped M-type Sr nanoferrites

In this article, novel M-type hexaferrites SrCoxNixFe12−2xO19 were synthesized using the sol–gel method. The phase structure was characterized by x-ray diffraction, grain morphology was investigated from scanned electron micrographs, and dielectric/electric/impedance characteristics were analyzed in the frequency range of 100 Hz to 2 MHz. X-ray diffraction (XRD) revealed the formation of hexaferrites without any secondary phase. The grain size and distribution were significantly affected by Co-Ni dopants and there was an observation of cluster of grains, grain agglomerates, and improved inter-grain connectivity. The substitution of Co-Ni caused a reduction in crystallite size from 41.47 to 23.14 nm and the dielectric constant/loss tangent varied non-monotonically. The electric modulus indicated a non-Debye type relaxation and the charge transport mechanism exhibited conductivity relaxation to be more dominant than dielectric relaxation. The prepared ferrites show a large dielectric constant and hence are suitable for use in transformer core and storage media. The correlation of simulated grain/grain boundary parameters with morphology, dielectric parameter, and electric modulus has been presented.

Structural, morphological, and EMI shielding evaluations of Sm-Mn co-doped Sr-based M-type hexaferrite for Ku band applications

High-performance, thin, and lightweight EMI (Electromagnetic interference) materials with outstanding shielding effectiveness were explored over the last years to solve the problems in electronic devices. Magnetic absorbing materials have extensive bandwidth, good impedance matching, and excellent absorption features. In the present study, Sm-Mn Sr-doped M hexaferrites with Sr1-xSmxFe12-yMnyO19 whereas (x= 0.00, 0.025, 0.05, 0.075, y = 0.00, 0.25, 0.5, 0.75) were prepared by the chemical route. XRD, FESEM, HRTEM, FTIR, VSM, and VNA are used to evaluate the properties of the Sm-Mn doped Sr-based M-type hexagonal ferrite. The XRD (X-ray diffraction) results revealed the presence of a hexagonal phase in the prepared samples. Rietveld refinement also confirmed the phase purity for the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FESEM (Field emission scanning electron microscopy) and HRTEM (High-resolution transmission electron microscopy) images revealed the hexagon-type shapes of the particles in the Sm-Mn doped Sr-based M-type hexagonal ferrites. The FTIR (Fourier transform infrared spectroscopy) spectra showed the 446–620 cm-1 lines, confirming the presence of the tetrahedral and octahedral phases of hexagonal ferrites. Dielectric and electromagnetic shielding effectiveness (SE) parameters are evaluated for Sm-Mn doped Sr-based M-type hexagonal ferrite. The electromagnetic parameters, such as complex refractive index, absorption and impedance, are also investigated for the Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having epoxy resin with 20 wt%, 30 wt% and 50 wt% samples, respectively. SE parameters are higher at more extensive filler loading. The green shielding index was found higher for Sm-Mn doped Sr-based hexagonal ferrite powder with x=0.075, y=0.75 having 20 wt% epoxy resin and decreased with filler loading. It is found the epoxy/Sm-Mn doped Sr-based M-type hexagonal ferrites-based composites are excellent absorbers in the Ku band. The investigated absorbers could be the best candidates for next-generation EMI green shielding absorbing devices and applications.

Gorerite, CaAlFe11O19, a new mineral of the magnetoplumbite group from the Negev Desert, Israel

AbstractGorerite, ideally CaAlFe11O19 is a new mineral and M-type hexaferrite of the magnetoplumbite group. It was found in ferrite-rich segregations of esseneite–gehlenite–wollastonite–anorthite melted rock of the ‘olive’ subunit of pyrometamorphic rocks located near Hatrurim Junction in the Negev Desert, Israel. Within these ferrite-rich segregations up to 100 μm in size, platy crystals of gorerite up to 50 μm in size intergrow with hibonite, hematite, maghemite, magnesioferrite, dorrite, barioferrite and andradite, forming aggregates. Additionally, small crystals of gorerite occur within magnesioferrite. Importantly, gorerite did not crystallise directly from the melt. Instead, it emerged through a reaction involving earlier crystallised hibonite and an iron-enriched melt, resulting in the partial or complete replacement of hibonite by gorerite. Gorerite appears grey in the reflected light (R = 18–23%), displaying distinct bireflectance: dark-grey perpendicular to Z and light-grey parallel to Z. Its Raman spectrum exhibits only one strong band at 700 cm–1, which shifts to higher frequencies with increasing Al content. Gorerite crystallises in the P63/mmc space group, with lattice parameters a = 5.8532(4) Å, c = 22.7730(2) Å and V = 675.67(7) Å3 with Z = 2. It exhibits a structure characterised by an intercalation of triple spinel-like S blocks and rock-salt type R blocks along the hexagonal c-axis.

Effects of La-Mn co-substitution on the structure and magnetic properties of M-type strontium hexaferrite

Research into enhancing the magnetic properties of permanent ferrite using ion substitution techniques has continued, particularly concerning replacing commercially available La-Co co-substitution ferrite with larger magnetic anisotropy and lower prices. Mn ions with larger magnetic moments have become one of the options. In this work, Sr1-xLaxFe11.6-xMnxO19 (0 ≤ x ≤ 0.5) with equal substitution of La-Mn was synthesized by the conventional ceramic route. X-ray diffraction analyses indicated that the upper limit of La-Mn concentration was 0.4. The lattice constant a increases and c decreases with increasing La-Mn concentrations. With the increase of La-Mn concentrations, Ms reaches the highest value of 80.52 emu/g (x = 0.2) at 300 K. As evidenced by Raman spectroscopy, the substitution sites of Mn ions in the ferrite lattice altered with the substitution concentration, and the substitution tendency was 4f2 > 12 k + 2a > 4f1. In addition, La-Mn substitution affects the inherent magnetic properties such as HA and Tc of the samples, which has a reference for further improvement of permanent ferrites.

Aluminium and praseodymium doped M-type hexaferrites for electric vehicle applications

The booming demand for electric vehicles, driven by the pursuit of enhanced efficiency, faces significant hurdles attributed to the costly integration of rare earth magnets like NdFeB. M-type strontium ferrite emerges as a promising alternative owing to its economic viability and exceptional magnetic characteristics, rendering it suitable for electric vehicle motor applications. This research focuses on the synthesis and characterization of SrFe12O19 and Sr1-xPrxFe10Al2O19 (where x = 0.00 to 0.20) hexaferrites, with praseodymium (Pr) substitution. Magnetic particles were synthesized utilizing the sol-gel auto-combustion technique, employing a calcination temperature of 1100 °C for a duration of 4 h. Structural and magnetic studies of aluminium-praseodymium (Al–Pr) doped samples are performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating-sample magnetometry (VSM). The structural analysis reveals a decrease in both particle size from 42 nm to 31.76 nm and lattice parameter with increasing doping concentration. Magnetic analysis yields crucial insights: Al3+ doping induces a substantial rise in coercivity from 5500 Oe to 10,500 Oe which is quite comparable to NdFeB, while Pr doping shows a subtle impact, enhancing remanence from 17 emu/g to 23.05 emu/g. These findings underscore the potential for optimizing magnetic properties through meticulous control of dopant concentrations in M-type hexaferrites, thereby positioning them as promising substitutes for rare earth magnets.

Microstructural, morphological and magnetic behaviour of Al3+ replaced BaFe11.5Co0.5O19 hexaferrites synthesized via sol-gel auto combustion route

In this work, polycrystalline BaFe11.5-xAlxCo0.5O19 (0≤x≤2) hexaferrite samples were synthesised by means of the sol–gel technique. Thereafter, the magnetic and structural properties are thoroughly examined. Cell refinement and XRD examination verified a magnetoplumbite hexaferrite arrangement with a space group of P63/mmc for each sample. The parameters ‘a’ and ‘c’ in the lattice fall in value from 5.885 Å to 5.875 Å and from 23.117 Å to 23.049 Å, respectively. Both the average crystallite size and the unit cell volume exhibit a declining trend as the doping level increases. For M-type hexaferrites, the optimal range of c/a values is determined to be 3.923–3.928. X-ray density (dx) and bulk density (db) decline with rising doping contents until x=1.5 doping content, at which point they exhibit an increasing trend. The results showed that as the doping amount increased, the saturation and remanence magnetizations decreased. Coercivity and magnetocrystalline anisotropy are rising together. Both the anisotropy field (Ha) and the anisotropy parameter (B) exhibit a rising trend with doping content. Coercivity of 5.896 kOe, anisotropic applied field of 1.84 kOe, saturation magnetization of 42.68 emu g−1, remanence magnetization of 24.414 (emu/g), and magnetic moment per formula unit-(mB) of 11.19 μ B are the best magnetic properties obtained for the BaFe10Al1.5Co0.5O19 sample.

Effect of lanthanum substitution and annealing temperature on the structural and morphological properties of M-type calcium hexaferrite

To investigate the influence of annealing temperature and lanthanum substitution on the structural properties of M-type calcium hexaferrite, we prepared unsubstituted and lanthanum-substituted Ca1-xLaxFe12O19 (x = 0.3, 0.4 and 0.5) powders by mean of sol–gel auto-combustion procedure, annealed between 800 °C and 1350 °C during 5 h in a rate of 180 °C per hour. XRD analysis showed that the M-type phase does not appear in the unsubstituted samples even with annealing at 1200 °C. The XRD patterns of the substituted samples contained peaks of the M-type phase with the presence of α-Fe2O3 as a secondary phase, the intensity of α-Fe2O3 decreased with increasing annealing temperature between 1200 °C and 1350 °C, and also as a function of lanthanum substitution concentration, which shows that the best lanthanum substitution concentration was x = 0.5. Lattice parameters of synthesized Ca0.5La0.5Fe12O19 align with literature results of various M-type hexaferrite. SEM micrographs of the Ca0.5La0.5Fe12O19 annealed at 1350 °C revealed that the mean and median crystallite size values were calculated to be 4.37 μm and 4.32 μm respectively.

Structural and magnetic properties of M-type hexaferrite nanoparticles: A comparative analysis of BaFe12O19 and SrFe12O19 synthesized via chemical co-precipitation

In this work, a comprehensive analysis of the structural and magnetic properties of the M-type hexaferrite (BaFe12O19 and SrFe12O19) was conducted using the chemical co-precipitation approach. The analytical techniques employed include powder X-ray diffraction, Transmission Electron Microscopy, Fourier Transform Infrared Spectroscopy, and Thermogravimetric Analysis. Powder Neutron Diffraction was utilized to analyse the magnetic ordering and crystal structure. A hexagonal crystal structure with space group P63/mmc was obtained from to structural analysis. Additionally, the investigation encompassed an assessment of the maximum energy product (BH)max and magnetic properties utilizing Vibrating Sample Magnetometry across all synthesized materials. Magnetic investigations of the studied materials showed several interesting characteristics: SrM showed a maximum saturation magnetization of 49.67 emu/g and a maximum coercivity of 4874.55 Oe. Remarkably, SrFe12O19 showed twice as much saturation magnetization and remnant magnetization than BaFe12O19, suggesting more robust and effective magnetic parameters. The overarching objective of this study is to discern the optimal hexaferrite material, evaluating magnetism, coercivity, thermal stability, and energy output through a systematic exploration of crystal structure, magnetic properties, thermal behaviour, manufacturing methodologies, and microstructure. This research endeavour not only contributes crucial insights into the potential applications of both BaM and SrM but also considers their environmental implications. The study further provides valuable recommendations for selecting the most efficacious material for specific permanent magnet applications, thereby contributing to the advancement on the field of magnetic engineering. The culmination of this work is poised to facilitate informed decision-making and technological progress in the realm of hexaferrite materials with a deliberate consideration of their environmental impact.

Effect of La3+and Al3+ doping on the crystal structure and magnetic properties of strontium hexaferrites

Modification of crystal structure and magnetic properties of M-type strontium hexaferrites (SrM) doped with foreign ions (Al3+, La3+) was studied, focusing on the distortion of the lattice. Incorporation of Al3+ ions contracted the lattice of SrM and hardened lattice vibration modes with lattice disorders. X-ray diffraction examined the lattice distortion of FeO5 trigonal bipyramidal sites (TBP) revealing that off-center displacement (z0) was reduced to z0 = 0 by heavy Al3+ doping. This reduction of z0 was attributed to stabilization of single-well potential in the positioning of Fe3+ ions in TBP. Furthermore, La3+ doping led to a more significant contraction of the lattice and restored a non-zero off-center displacement of Fe3+ ion in TBP. The polycrystalline ceramics with high coercivity exceeding 21 kOe through the conventional ceramic processing route with concomitant La3+ and Al3+ doping.

Magnetization reversal and coercivity mechanism in ferrimagnetic M-type hexaferrite by controlling phase evolution

The correlation of phase evolution (annealing at different temperatures) with magnetic properties like magnetization reversal, coercivity mechanism, and energy product in M-type hexaferrite by substituting Sr in place of Ba has been reported in the present article. The Ba1-xSrxFe12O19 (x = 0.0, 0.5, & 1.0) have been prepared by the sol–gel auto-combustion method followed by annealing at different temperatures from 800 °C to 1200 °C. The structural and magnetic properties have been characterized by X-ray diffraction, Field emission scanning electron microscopy, Raman spectroscopy, and Vibrating sample magnetometer. The Rietveld refinement confirms contraction in unit cell parameters by replacing Sr in place of Ba and lattice expansion with increasing annealing temperature. There is no significant effect of substitution on magnetic properties found rather heat treatment affects greatly. The transition from a single domain to multidomain particles and their contribution to initial magnetization curves are analyzed. The differential susceptibility (dM/dH) calculated from room temperature magnetization confirms the existence of a pinning effect during magnetization reversal for samples heat treated below 1200 °C. Secondary phases or grain boundaries are believed to act like pinning centers. This work opens insight into the domain wall motion by microstructure engineering. The coercivity is tuned to 6.09 kOe by controlling the annealing temperature for the Ba1-xSrxFe12O19 (x = 1.0) sample. The maximum energy product (BH)max in the range of 0.94–1.27 MGOe has been achieved.

Single-domain particles of manganese-for-iron substituted M-type barium hexaferrite: synthesis, crystal structure, and magnetic properties

Single-domain particles of manganese-for-iron substituted M-type barium hexaferrite: synthesis, crystal structure, and magnetic properties

Samarium substituted M-type Sr hexaferrites: The structural, magnetic and electrochemical properties for supercapacitor applications

In the current project the samarium substituted strontium hexaferrites with general formula SrSmxFe12-xO19 (where x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanocrystalline powder have been successfully synthesized employing sol-gel auto-combustion route. The fabricated samples have been sintered at 1200 °C for 2 h. The structural, functional group, morphological, elemental, optical, magnetic, dielectric and electrochemical properties have been studied by X-Ray diffractometer, Fourier transformer infrared spectroscopy, scanning electron microscopy, Energy dispersive X-Ray, UV–visible, vibrating sample magnetometer, Inductor capacitor and resistor meter and cyclic voltammetry, galvanostatic charging discharging respectively. The structural analysis confirms the formation of the single-phase Magnetoplumbite structure of all the samples. The crystallite size decreases with increasing Sm+3 ions concentration. The characteristic bands of hexagonal structure present in the range of 400–660 cm−1 which correspond to metal–oxygen (M − O) stretching and vibrational bonds. The bandgap increases from 4.21 to 4.86 eV. The magnetic properties reveal the clear ferromagnetic M − H curve in which the value of coercivity increases and saturation magnetization decreases. The dielectric constant and tangential loss of the material both decrease with increasing frequency. Conversely, the ac conductivity of the material increases with increasing applied frequency. This is the natural behavior of ferrites. This behavior can be attributed to the polarization and orientation of the dipoles within the material in response to the applied electric field. The observed increase in σ at higher frequencies suggests that the material may be useful in applications where high-frequency electrical properties are desired such as in the development of high-speed electronic devices. The specific capacitance increases monotonically up to 1020 F g −1 with increasing Sm+3 concentration. The samarium substituted hexaferrites are recommended to fabricate the high energy density charge storage devices such as supercapacitors.