Co-Doped Rare-Earth (La, Pr) and Co-Al Substituted M-Type Strontium Hexaferrite: Structural, Magnetic, and Mossbauer Spectroscopy Study

The present study investigates the influence of La3+ and Pr3+ doping on the structural, magnetic properties, and hyperfine fields of Sr0.7RE0.3Fe12-2x CoxAlxO19, (RE: La3+ and Pr3+, x = 0.0 - 0.8) hexaferrite compounds prepared via auto-combustion technique. The XRD analysis shows a linear decrease in a and c lattice and unit cell volume contraction with the content x. The room temperature magnetic study shows that for the Pr3+ doped Sr0.7Pr0.3Fe12-2x CoxAlxO19 (Pr3+-SrM), the magnetization value monotonically decreases while for La3+ doped Sr0.7La0.3Fe12-2xCoxAlxO19 (La3+-SrM) magnetization value shows a noticeable increase in magnetization value with x. The coercivity of the Pr3+-SrM compound was observed to decrease while that of the La3+-SrM compound showed a marked 40% increase at x = 0.2 (~5829 Oe) in comparison to undoped SrFe12O19 (~3918 Oe). A difference in Curie temperature was also observed, with Tc ~ 525°C at x = 0.4 for Pr3+-SrM and Tc = 505°C for x = 0.4 for La3+-SrM compound. The observed differences in magnetic properties have been explained on the basis of the site occupancy of Co2+ and Al3+ in the presence of rare-earth ions. The presence of non-magnetic rare-earth ion, La3+, improved saturation magnetization, and coercivity and deemed suitable replacement for Sr2+. The hyperfine parameters namely quadrupole shift showed a decrease with the La3+ or Pr3+ doping independent of (Co2+-Al3+) ions doping. Overall, the Mossbauer analysis suggests that the (Co2+-Al3+) impurities prefer occupancy at 2a site.

Microstructure and microwave electromagnetic properties of Dy^(3+)-doped W-type hexaferrites

Ba 1 x Dy x Co 2 Fe 16 O 27 （x = 0.00, 0.05, 0.10, 0.15, and 0.20） was prepared by the solid-state method. The phase structure was studied using powder X-ray diffraction （XRD）, the electromagnetic properties were measured, and the reflection loss of Dy 3＋ -doped ferrite material was calculated using electromagnetic parameters by the transmission line theory. All XRD patterns showed the single phase of the magnetoplumbite barium ferrite without other intermediate phase when x ≤ 0.15. The values of ε ′ and ε ″ increased slightly with Dy 3＋ ions doping. The values of μ″ and μ′ were improved with Dy 3＋ doping, exhibiting excellent microwave magnetic performance. The reasons have also been discussed using the electromagnetic theory. Dy substitution could increase microwave-absorbing performance and broaden frequency band （reflection loss （RL） -10 dB）, and the absorbing peak shifted to high-frequency position. When x = 0.2, ferrite layer exhibited the most excellent microwave-absorbing performance at a thin matching thickness of 1.5 mm. The peak value of RL was around -15 dB, and the frequency band （RL -10 dB） was about 7 GHz （from 8 to 15 GHz）.

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)

Y-type hexaferrites with tunable conical magnetic structures are promising single-phase multiferroics that exhibit large magnetoelectric effects. We have investigated the influence of Co substitution on the magnetoelectric properties in the Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)(x = 0.0, 0.4, 1.0, 1.6). The spin-induced electric polarization can be reversed by applying a low magnetic field for all the samples. The magnetoelectric phase diagrams of BaBa(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22) are obtained based on the measurements of magnetic field dependence of dielectric constant at selected temperatures. It is found that the substitution of Co ions can preserve the ferroelectric phase up to a higher temperature, and thus is beneficial for achieving single-phase multiferroics at room temperature.

Tailoring the optical and magnetic properties of La-BaM hexaferrites by Ni substitution

We investigate the impact of Ni insertion on the structural,optical,and magnetic properties of Ba_(0.8)La_(0.2)Fe_(12-x)Ni_(x)O_(19)hexaferrites(Ni substituted La-BaM hexaferrites).Samples were prepared using the conventional co-precipitation method and sintered at 1000℃for 4 hours to assist the crystallization process.An analysis of the structure of the samples was carried out using an x-ray diffraction(XRD)spectrometer.The M-type hexagonal structure of all the samples was confirmed using XRD spectra.The lattice parameters a and c were found to be in the ranges of 5.8925±0.001 nm–5.8952±0.001 nm and 23.2123±0.001 nm–23.2219±0.001 nm,respectively.The M-type hexagonal nature of the prepared samples was also indicated by the presence of corresponding FT-IR bands and Raman modes in the FT-IR and Raman spectra,respectively.EDX results confirmed the successful synthesis of the samples according to the required stoichiometric ratio.A UV-vis spectrometer was used to record the absorption spectra of the prepared samples in the wavelength range of 200 nm–1100 nm.The optical energy bandgap of the samples was found to be in the range of 1.21 eV–3.39 eV.The M–H loops of the samples were measured at room temperature at an applied magnetic field range of 0 kOe–60 kOe.A high saturation magnetization of 99.92 emu/g was recorded in the sample with x=0 at a microwave operating frequency of 22.2 GHz.This high value of saturation magnetization is due to the substitution of La3+ions at the spin-up(12k,2a,and 2b)sites.The Ni substitution is proven to be a potential candidate for the tuning of the optical and magnetic parameters of M-type hexaferrites.Therefore,we suggest that the prepared samples are suitable for use in magneto-optic applications.

Impact of In^(3+) cations on structure and electromagnetic state of M-type hexaferrites

The solid solutions of In^(3+) doped M-type strontium hexaferrites were produced using a conventional solid-state reaction method,and Rietveld analysis of the neutron diffraction patterns was conducted.In^(3+) cations occupy octahedral (4f_(Ⅵ)and 12 k) and tetrahedral (4f_(Ⅳ)) positions (SG=P6_(3)/mmc(No.194)).The average particle size is 837–650 nm.Curie tempearature (T_(C)) of the compounds monotonically decreased down to~520 K with increasing x.A frustrated magnetic state was detected from ZFC and FC magnetizations.saturation magnetization (M_(s)) and effective magnetocrystalline anisotropy coefficient (k_(eff)) were determined using the law of approach to saturation.A real permittivity (ε″) maximum of~3.3 at~45.5 GHz and an imaginary permittivity (ε′) of~1.6 at~42.3 GHz were observed for x=0.1.A real permeability (μ′) maximum of~1.5 at~36.2 GHz was observed for x=0.Aμ″imaginary permeability maximum of~0.8 at~38.3 GHz was observed for x=0.1.The interpretation of the results is based on the type of dielectric polarization and the natural ferromagnetic resonance features.

Preparation and microwave hexaferrites by a sol-gel process

s Ba_4Zn_zCo_(2-z)Fe_(36)O_(60) hexaferrites with Z = 2.0, 1.5, 1.0, 0.5, and0.0 were prepared by a citrate Sol-gel process. The complex dielectric constant and complexpermeability of hexaferrite-paraffin wax composites were measured in the range from 0.1 to 6.0 GHz.Measured results showed that both the complex dielectric constant and the dielectric loss exhibitedno significant change as the measuring frequency increasing except for the sample with Z = 0.0. Thereal part of permeability decreased with increasing frequency for all samples in the whole measuringfrequency range, and the natural resonance phenomena were observed in all μ″ spectrum but Co_2U.The results also indicate that the content of zinc closely affects the microwave properties ofBa_4Zn_zCo_(2-z)Fe_(36)O_(60) ferrites, and the greater the zinc content, the lower the naturalresonance frequency is.

Thermal Instability and Microstructure of Strontium M-type Hexaferrite Nanoparticles Synthesized by Citrate Approach

The dried gel of SrFe12O19, prepared by citrate approach, was investigated by means of infrared spectroscopy （ IR ）, thermogravimetric analysis （ TG ）, differential scanning calorimetry （ DSC ）, X- ray diffraction（ XRD ） techniques, energy dispersive spectroscopy（ EDS ）, and transmission electron microscopy（ TEM ）. The thermal instability and the thermal decomposition of low-temperature strontium M-type hexaferrite crystallized at about 600℃ were confirmed for the first time by XRD method. The decomposition of the low-temperature strontium M-type hexaferrite took place at about 688.6℃ determined by DSC investigation. The low-temperature strontium M-type hexaferrite nanopartieles were decomposed into SrFeO2.5 with an orthorthombic cell and Fe2O3 with a tetragonal cell as well as possibl α-Fe2O3 . The agglomerated particles with sizes less than 200 nm obtained at 800℃ were plesiomorphous to strontium M-type hexaferrite. The thermally stable strontium M-type hexaferrite nanopartieles with sizes less than 100um cotdd take place at 900 ℃ . Up to 1000 ℃ , the phose transformotion to form strontium M-type hexaferrite was ended, the calcinations with the sizes more than 1μm were composed of α-Fe2O3 and strontium M-type hexaferrite. The method of distinguishing γ-Fe2O3 with a spinel structure from Fe2O3 with tetragonal cells by using powder XRD method was proposed. Fe2O3 with tetragonal cells to be crystallized before the crystallization of thermally stable strontium M-type hexaferrite was confirmed for the first time. The reason why α- Fe2O3 as an additional phase appears in the calcinations is the cationic vacancy of stroutium M-type hexaferrite , SrFe12-x□O19 （0≤x ≤0.5）.

Radiation Losses in the Microwave X Band in Al-Cr Substituted Y-Type Hexaferrites

We present a study on radiation losses in the microwave X band in Al-Cr substituted Y-type hexaferrites, namely Ba2Mg2Alx/2Crx/2Fe12-xO22 （x = 0, 0.5 and 1.0）. The study is performed by means of a vector network analyzer, Fourier transform infrared spectroscopy, a vibrating sample magnetometer and x-ray powder diffraction. Ba2Mg2Fe12O22 hexaferrite shows radiation loss of -37.25dB （99.999% loss） at frequency 9.81 GHz, which can be attributed to its high value of saturation magnetization, i.e., 22.08emu/g. Moreover, we obtain that magnetic properties have strong influence on the radiation losses.

Evolution of structure and physical properties in Al-substituted Ba-hexaferrites

The investigations of the crystal and magnetic structures of the BaFe12_xAlxO19 （x = 0.1-1.2） solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12_xAlxOt9 （x = 0.1-1.2） solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range （from 4.2 K to 150 K）. It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFet2_xAlxO19 （x = 0.1-1.2） solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

Synthesis and Magnetic Properties of Conventional and Microwave Calcined Strontium Hexaferrite Powder

Powders of strontium hexaferrite (SrFe12O19 - SrF) have been prepared by the sol-gel process. The prepared precursor was calcined in two different calcination techniques, using conventional furnace and microwave furnace. Thermal analysis studies showed exothermic and endothermic reaction peak at room temperature to 1200°C. An investigation of SrFe12O19 crystalline powder from the structural and magnetic aspect is performed using X-ray diffraction (XRD), High resolution scanning electron microscopy (HR-SEM) and vibrating sample magnetometer (VSM). The average particle diagonal size of SrFe12O19 powder was 80 - 100 nm in conventional and 40 - 70 nm in microwave calcinations respectively. XRD result showed the formation of SrFe12O19 of the sample calcined at 900oC with Fe/Sr: D-Fructose ratio = 12.

Influence of cerium ions on structure-dependent magnetic properties of Ba-Sr M-type hexaferrite nanocrystals

The present study is a systematic effort to investigate the structure-sensitive magnetic parameters of Ce^(3+) substituted Ba-Sr hexaferrite nanocrystals chemically formulated as Ba_(0.5)Sr_(0.5)Ce_(x)Fe_(12-x)O_(19) where x=0.0-0.2 with Δx=0.05.The hexaferrite powders were prepared using the sol-gel self-ignition route and structurally characterized by means of powder X-ray diffraction and Fourier transform infrared spectroscopy.The creation of the M-type hexaferrite phase within the synthesized samples was revealed from the Rietveld refinement of the X-ray diffractograms.The occurrence of a secondary phase of CeO_(2) was revealed within the hexaferrites for the substitution,x> 0.The refined X-ray diffraction data were utilized to compute the lattice parameters,X-ray density,and lattice parameter ratio.The crystal structure plotted from the refined XRD data reveals the occupancy of the ions at different lattice sites.The XPS data of the hexaferrite were analyzed to confirm the oxidation states of the constituent elements.The nanocrystalline nature of the hexaferrites was revealed from the crystallite sizes calculated using Scherer's formula.The analysis of FTIR spectra confirms that only a fraction of Ce^(3+)accommodated in the lattice and the remaining Ce content reside in the form of the CeO_(2) phase.The morphology of the hexaferrites was analyzed from the FESEM profiles of the ferrite samples.The magnetic behavior study was performed by analyzing the Curie temperature,hysteresis loops,and hyperfine interactions by means of susceptibility,V.S.M,and Mossbauer spectroscopy,respectively.The hexaferrites with increasing coercivity,decreasing saturation magnetization,and decreasing Curie temperature are reported in the study.The substituted Ce^(3+)ions inhibit the grain growth and create lattice imperfections giving rise to hexaferrites with tuned magnetic parameters suitable for different applications.

Establishment of magneto-dielectric effect and magneto-resistance in composite of PLT and Ba-based U-type hexaferrite

We are examining the behavior of a composite made of ferroelectrics with strong dielectric properties and ferrites with magnetic properties due to the rising need for materials for multipurpose devices.Many application avenues will be favored by the pairing of these materials’individual qualities with one another.Perovskite and U-type hexaferrite composite materials have been chosen for this study based on their magnetic and dielectric properties.The composites,(1−x)PLT−x(Ba1−3xNd2x)4Co2Fe36O60 where x=0.52,0.54,0.56,0.58 are prepared by solid state reaction method and phase formation was examined.Consideration has been given to the magnetic,dielectric,and magneto-dielectric properties.This work has established the link between the electric and magnetic domains while applying electric and magnetic forces to the materials.The magneto-dielectric research revealed magneto-electric coupling in all of the samples.However,the sample shows the maximum coupling for x=0.54 with MDR%values of 93.17%,which might be because this sample appears to have a high magneto-resistance(161%).

Influences of divalent ion substitution on the magnetic and dielectric properties of W-type barium ferrite

Saturation magnetization,magneto-crystalline anisotropy field,and dielectric properties are closely related to microwave devices applied at different frequencies.For regulating the magnetic and dielectric properties of W-type barium ferrites,single-phase BaMe_(2)Fe_(16)O_(27)(Me=Fe,Mn,Zn,Ni,Co) with different Me ions were synthesized by the high-temperature solid-state method.The saturation magnetization(Ms) range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field(H_a) range from 10700.60 Oe(1 Oe=79.5775 A·m^(-1)) to 13739.57 Oe,depending on the type of cation substitution in the hexagonal lattice.The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region,while they almost remain constant in the high-frequency region.The charac teristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.

Morphology and magnetic traits of strontium nanohexaferrites:Effects of manganese/yttrium co-substitution

Doped strontium(Sr) hexaferrites appeared potential candidates for microwave absorber applications.Driven by this idea, we examined the influence of manganese(Mn) and yttrium(Y) co-substitution on the microstructures,morphology and magnetic properties of Sr nanohexaferrites(Sr1-xMnxFe12-yYyO19,where 0.0 ≤ x = y ≤ 0.5) synthesized via citrate sol-gel auto-combustion technique. As-prepared samples were thoroughly characterized using diverse analytical tools. X-ray diffraction pattern reveals a single Mhexagonal crystalline phase. FE-SEM, TEM, HR-TEM show a hexagonal platelet-like structure. The magnetic hysteresis loops(measured at room and low temperature) of the as-prepared nanohexaferrites exhibit ferromagnetic(FM) behavior. Magnetic parameters including the saturation magnetization,remanence, coercive and magneto-crystalline anisotropy field are found to decrease with the increase in Mn2+ and Y3+ contents. Zero-and normal-field cooled magnetization measurements in the range of 2-400 K display the complete absence of blocking temperature, confirming the characteristic ferromagnetic behavior of the proposed composition.

Preparation and characterization of carbonyl iron/strontium hexaferrite magnetorheological fluids

The heat transfer oil-based magnetorheological fluid （MRF） was prepared using oleic acid-modified micron carbonyl iron powder as a magnetic dispersed phase and strontium hexaferrite （SrFe12019） nanoparticles as an additive. The sedimentation stability of MRFs was studied. The results indicated that the stability of MRFs was improved remarkably by adding SrFel2019 nanoparticles and the sedimenta- tion ratio was only 0.88 in 20 days when the content of nanoparticles reached 10wt%. The rheological properties were characterized by a HAAKE rheometer without a magnetic field and a capillary rheometer with and without a magnetic field. The effects of SrFe12019 nanoparticles, the temperature, and magnetic field strength were investigated. In addition, the rheological properties could be predicted well using the improved Herschel-Bulkley model, even under a magnetic field. A theoretical model was also proposed to predict the yield stress based on the microstructure of the MRF under an applied magnetic field.

Low temperature sintering behavior of La-Co substituted M-type strontium hexaferrites for use in microwave LTCC technology

The La-Co substituted Sr1–xLaxFe12–xCoxO19 (x=0–0.5) ferrites with appropriate Bi2O3 additive were prepared by conventional sintering method and microwave sintering method at low sintering temperatures compatible with LTCC (low temperature co-fired ceramics) systems, and their sintering behavior was chiefly investigated, including the crystal structure, saturation magnetizationMs, magnetic anisotropy fieldHa, intrinsic coercivityHci, and Curie temperatureTC. Experiment results clearly showed that the pure M-type crystal phase was successfully obtained when the La-Co substitution amountx did not exceed 0.3. However, the single M-type phase structure transformed to multiphase structure with further increased x, where the M-type phase coexisted with the non-magnetic phase such asα-Fe2O3 phase, La2O3 phase, and LaCoO3 phase. Appropriate La-Co substitution improved theMs (>62 emu/g),Ha (>1400 kA/m), andHci (>320 kA/m) for the ferrites withx varying from 0.1 to 0.3, but theTC decreased with increasing substitution amount. More-over, the microwave sintered ferrites could provide largerHci and similarMs compared with the conventional sintered ferrites.

Co-substitution of zirconium and neodymium on hyperfine interactions and AC susceptibility of SrFe12O19 nanohexaferrites

This study presents the influence of Zn and Nd co-substitution on structure,morphology,AC susceptibility and ZFC-FC magnetizations of Sr nanohexaferrites(NHFs),SrFe12-x(Zn,Nd)xO19(0.0≤x≤1.0),which was produced by sol-gel approach.XRD powder patterns,scanning electron microscopy(SEM) and high-resolution transmission electron spectroscopy(HR-TEM) approve the synthesis of Sr M-type hexaferrite.Mossbauer spectra show that Zn^2+ions occupy 2 b and 4f1 sites while Nd3+ions locate at 2 a,4f2 and 12 k sites.The magnetic properties of the produced Sr-NHFs were investigated also by ZFC-FC magnetizations and AC susceptibility.According to the MFC-MZFC results(between 2 and 400 K),no blocking temperature was detected which indicates the ferromagnetic(FM) behavior of NHFs.At lower temperatures,a super-spin glass like behavior is discerned.The AC susceptibility indicates that the magnetic interactions are improved due to the inclusion of low content(x=0.1) of Nd^3+and Zn^2+ions into the Sr-NHFs.However,with further increasing the Nd^3+and Zn^2+contents(x=0.9),the magnetic interactions are weakened.

Efects of Molybdenum Concentration and Valence State on the Structural and Magnetic Properties of BaFe_(11.6)Mo_xZn_(0.4-x)O_(19) Hexaferrites

Barium hexaferrites BaFe11.6Mox Zn0.4-x O19（x=0.1,0.2,0.4）were prepared by precipitation of the precursors using wet chemical mixture method and then sintering the dried powders at 1100℃.The properties of the prepared samples were investigated using X-ray difraction（XRD）,scanning electron microscopy（SEM）,vibrating sample magnetometer,and Mssbauer spectroscopy.XRD patterns revealed that all prepared samples had BaFe12O19hexaferrite structure as a majority phase.SEM images demonstated that the samples consisted mainly of hexagonal platelet-like grains with diameters ranging from 100 to 500 nm.Mssbauer spectra revealed that Zn2＋ions occupy 4f1 sites leading to the splitting of the 12k component.However Mo6＋ions occupy 2b sites while Mo4＋ prefer 4f1 and 12k sites.For the sample with x=0.4,Mo6＋and Mo4＋ ions were found to have preference for 2b and 12k sites,respectively,and to induce the development of Fe2＋ions in the hexaferrite,leading to noticeable changes in the magnetic properties of the system.The observed magnetic properties were found to be consistent with the preferential site occupation of metal ions,and the hyperfine fields derived from Mssbauer spectra of these samples.

Tb^(3+)substituted strontium hexaferrites:Structural,magnetic and optical investigation and cation distribution

In this study,SrFe12-xTbxO19(0.00≤x≤0.1)hexaferrites(HFs)were prepared successfully by citrate solgel approach.X-ray powder diffraction analyses affirm the hexagonal structure of products.Impurity phase starts to appear for x≥0.04.The crystallites sizes were estimated to be in the range of 33-46 nm.All the products exhibit inhomogeneous distribution of grain size detected through SEM.The analyses of magnetization versus applied magnetic field,M(H),were performed.Magnetization measurements were done at room(300 K;RT)and low(10 K)temperatures.The different magnetic parameters including saturation magnetization Ms,remanence Mr,squareness ratio(SQR=Mr/Ms),coercivity Hc,and magnetic moment nB are deduced and discussed in detail.At both considered temperatures,M(H)results show ferrimagnetic nature for all compositions.It is shown that the Tb substitutions significantly affect M(H)data.A significant increase in the Ms,Mr,and nB is observed for x=0.02 sample.The SQR values are around 0.5 indicating the single domain nature with uniaxial anisotropy.The obtained magnetic results were investigated deeply with relation to structural and microstructural properties.Mossbauer spectroscopy results were also investigated.According to Mossbauer results,the Tb3+ions preferentially occupy 12 k and 4f2 sites.

Enhanced magneto-dielectric response in La-doped Co_(2)U hexaferrite

The U-type hexaferrites(Ba_(1−3x)La_(2x))4Co_(2)Fe_(36)O_(60)(x=0,0.05,0.10,0.15,0.20,0.25)have been synthesized by auto-combustion method.The work involves the study of structural,microstructural,dielectric,magnetic and magneto-dielectric properties of the prepared materials.The structural analysis has been done by X-ray diffraction technique along with Le Bail refinement which confirmed the pure hexagonal phase for all the samples.The microstructural analysis has been carried out by field-emission scanning electron microscopy.The vibrating sample magnetometer is used to measure the magnetic properties.The sample with a composition of x=0.15 has shown the maximum magnetization of approximately 73.31 emu/g with the remnant magnetization of 38.89 emu/g and coercive field of 1.77 kOe at room temperature.Moreover,the same sample has delivered the maximum mag-netodielectric response of about 54.18%at 1.5-T field.