This study was conducted to investigate the properties of Pr^(3+)-Dy^(3+)doped Zn_(2)Y-type hexaferrite for potential technological applications.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and ...This study was conducted to investigate the properties of Pr^(3+)-Dy^(3+)doped Zn_(2)Y-type hexaferrite for potential technological applications.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and field-emission scanning electron microscopy(FESEM)were used to analyze structural properties.The crystallite size in the synthesized samples varies between 57.54 and 68.57 nm.The vibrational bands at 400 and 600 cm^(-1),common to all hexaferrites,were confirmed through FTIR.The FESEM analysis reveals an agglomeration of magnetic grains and a decrease in the average grain size from 1.24 to1.06μm.The M-H loops show that,with x values of 0.0,0.1,and 0.2,the saturation magnetization is determined to be 34.76,34.23,and 32.52 emu/g,respectively.The corresponding coercivity values are21.24,30.39,and 33.99 Oe.UV-visible spectroscopy using Tauc theory reveals an increase in the optical band gap from 2.32 to 2.50 eV,indicating a tunable energy band structure by incorporating Pr^(3+)-Dy^(3+)ions.The dielectric constant increases,whereas AC conductivity decreases with increased Pr^(3+)-Dy^(3+)concentration.The obtained results suggest the potential suitability of these materials for various technological applications.展开更多
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) ...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.展开更多
The present study investigates the influence of La<sup>3+</sup> and Pr<sup>3+</sup> doping on the structural, magnetic properties, and hyperfine fields of Sr<sub>0.7</sub>RE<sub&...The present study investigates the influence of La<sup>3+</sup> and Pr<sup>3+</sup> doping on the structural, magnetic properties, and hyperfine fields of Sr<sub>0.7</sub>RE<sub>0.3</sub>Fe<sub>12-2x</sub> Co<sub>x</sub>Al<sub>x</sub>O<sub>19</sub>, (RE: La<sup>3+</sup> and Pr<sup>3+</sup>, <em>x</em> = 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 <em>x</em>. The room temperature magnetic study shows that for the Pr<sup>3+</sup> doped Sr<sub>0.7</sub>Pr<sub>0.3</sub>Fe<sub>12-2x</sub> Co<sub>x</sub>Al<sub>x</sub>O<sub>19</sub> (Pr<sup>3+</sup>-SrM), the magnetization value monotonically decreases while for La<sup>3+</sup> doped Sr<sub>0.7</sub>La<sub>0.3</sub>Fe<sub>12-2x</sub>Co<sub>x</sub>Al<sub>x</sub>O<sub>19</sub> (La<sup>3+</sup>-SrM) magnetization value shows a noticeable increase in magnetization value with <em>x</em>. The coercivity of the Pr<sup>3+</sup>-SrM compound was observed to decrease while that of the La<sup>3+</sup>-SrM compound showed a marked 40% increase at <em>x</em> = 0.2 (~5829 Oe) in comparison to undoped SrFe<sub>12</sub>O<sub>19</sub> (~3918 Oe). A difference in Curie temperature was also observed, with Tc ~ 525<span style="white-space:nowrap;">°</span>C at <em>x</em> = 0.4 for Pr<sup>3+</sup>-SrM and Tc = 505<span style="white-space:nowrap;">°</span>C for <em>x</em> = 0.4 for La<sup>3+</sup>-SrM compound. The observed differences in magnetic properties have been explained on the basis of the site occupancy of Co<sup>2+</sup> and Al<sup>3+</sup> in the presence of rare-earth ions. The presence of non-magnetic rare-earth ion, La<sup>3+</sup>, improved saturation magnetization, and coercivity and deemed suitable replacement for Sr<sup>2+</sup>. The hyperfine parameters namely quadrupole shift showed a decrease with the La3<sup>+</sup> or Pr<sup>3+</sup> doping independent of (Co<sup>2+</sup>-Al<sup>3+</sup>) ions doping. Overall, the Mossbauer analysis suggests that the (Co<sup>2+</sup>-Al<sup>3+</sup>) impurities prefer occupancy at 2<em>a</em> site.展开更多
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,...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.展开更多
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 ...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）.展开更多
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 w...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.展开更多
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 so...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.展开更多
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...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.展开更多
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 magnetoelec...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)Co_(x)Mg_(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 Ba_(0.3)Sr_(1.7)Co_(x)Mg_(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.展开更多
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 conv...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.展开更多
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 prepa...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.展开更多
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 ap...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.展开更多
In this comparative study,Tb and Tm substituted Sr-hexafe rrites(HFs) with the chemical compositions of SrTb_(x)Fe_(12-x)O_(19) and SrTm_(x)Fe_(12-x)O_(19)(x=0.00,0.02 and 0.04) were fabricated via citrate sol-gel app...In this comparative study,Tb and Tm substituted Sr-hexafe rrites(HFs) with the chemical compositions of SrTb_(x)Fe_(12-x)O_(19) and SrTm_(x)Fe_(12-x)O_(19)(x=0.00,0.02 and 0.04) were fabricated via citrate sol-gel approach.The AC susceptibility and FC-ZFC magnetization were investigated.The product structure and morphologies were also investigated via XRD,TEM and SEM along with EDX.Measurements of temperature dependence of magnetization M-T and AC magnetic susceptibility versus temperature were carried out.The various synthesized HFs displayed ferrimagnetic behavior within 10-325 K.At lower temperatures,super-spin glass-like behavior was noticed.Neel-Arrhenius and Vogel-Fulcher models were employed to explore the experimental data of AC susceptibility.展开更多
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 composit...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.展开更多
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 diffract...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）.展开更多
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 ana...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.展开更多
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...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.展开更多
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 furna...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.展开更多
Realizing robust magnetoelectric(ME)coupling effect near room temperature is still a long-standing challenge for the application of multiferroic materials in next-generation low-power spintronic and memory devices.Her...Realizing robust magnetoelectric(ME)coupling effect near room temperature is still a long-standing challenge for the application of multiferroic materials in next-generation low-power spintronic and memory devices.Here we report a systematic study on the magnetic,dielectric,and ME coupling properties of Y-type hexaferrite Ba_(0.5)Sr_(1.5)Co_(2)Fe_(12-x)Al_(x)O_(22)(x=0.0,0.5,1.0)single crystals.The Al doping can induce the shifting of the alternating longitudinal conical(ALC)-proper screw(PS)magnetic phase transition temperature from 200 K for x?0e365 K for x-1.0.The most interesting feature is that the Ba_(0.5)Sr_(1.5)Co_(2)Fe_(11)AlO_(22) single crystal displays a direct and converse ME coupling coefficient with aH~3,100 ps/m and aE~3,900 ps/m at 250 K,respectively,due to the Al-doped enhanced stability of ALC phase.Moreover,the exchange bias also verifies the strong coupling of electric and magnetic orders.These results provide a valuable insight on the modulation of ALC structure and the mechanism of ME effect in Y-type hexaferrites.展开更多
Hexaferrites'magnetic and structural properties are highly sensitive to changes in sintering temperature and cationic replacements.We fabricated Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)hexaferrites using the sol-gel tec...Hexaferrites'magnetic and structural properties are highly sensitive to changes in sintering temperature and cationic replacements.We fabricated Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)hexaferrites using the sol-gel technique.We examined the phase,microstructure and magnetic aspects of the samples with respect to varying doping of rare earth dysprosium.The results show the expansion in the lattice upon incorporation of dysprosium against iron.Morphological studies confirm the uniform distribution of particles with slightly longitudinal nanoflakes in one direction.Magnetic investigations show an increase in magnetic saturation(Ms)with increasing dysprosium incorporation till optimum level is achieved for 15%doping concentration,with negligible change for maximum doping level.Furthermore,coercivity(Hc)and magnetic moment(mB)in terms of Bohr's magneton(μB)also show an increasing trend with dysprosium substitution levels.The maximum saturation magnetization of 33.355 emu/g is achieved with magnetic remanence of 18.290 emu/g,along with optimum magnetic moment of 6.249μB.In addition to the traditional magnetic parameters,magnetic anisotropy parameters were explored for the deep insights into magnetic parameters.These outcomes suggest that improved magnetic properties of Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)ferrites make it good substitute for storage devices,magnetic filters,and other magnetic applications.展开更多
基金the Deanship of Scientific Research at King Khalid University for funding this work through large group Research Project under grant number RGP2/226/44。
文摘This study was conducted to investigate the properties of Pr^(3+)-Dy^(3+)doped Zn_(2)Y-type hexaferrite for potential technological applications.X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and field-emission scanning electron microscopy(FESEM)were used to analyze structural properties.The crystallite size in the synthesized samples varies between 57.54 and 68.57 nm.The vibrational bands at 400 and 600 cm^(-1),common to all hexaferrites,were confirmed through FTIR.The FESEM analysis reveals an agglomeration of magnetic grains and a decrease in the average grain size from 1.24 to1.06μm.The M-H loops show that,with x values of 0.0,0.1,and 0.2,the saturation magnetization is determined to be 34.76,34.23,and 32.52 emu/g,respectively.The corresponding coercivity values are21.24,30.39,and 33.99 Oe.UV-visible spectroscopy using Tauc theory reveals an increase in the optical band gap from 2.32 to 2.50 eV,indicating a tunable energy band structure by incorporating Pr^(3+)-Dy^(3+)ions.The dielectric constant increases,whereas AC conductivity decreases with increased Pr^(3+)-Dy^(3+)concentration.The obtained results suggest the potential suitability of these materials for various technological applications.
文摘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.
文摘The present study investigates the influence of La<sup>3+</sup> and Pr<sup>3+</sup> doping on the structural, magnetic properties, and hyperfine fields of Sr<sub>0.7</sub>RE<sub>0.3</sub>Fe<sub>12-2x</sub> Co<sub>x</sub>Al<sub>x</sub>O<sub>19</sub>, (RE: La<sup>3+</sup> and Pr<sup>3+</sup>, <em>x</em> = 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 <em>x</em>. The room temperature magnetic study shows that for the Pr<sup>3+</sup> doped Sr<sub>0.7</sub>Pr<sub>0.3</sub>Fe<sub>12-2x</sub> Co<sub>x</sub>Al<sub>x</sub>O<sub>19</sub> (Pr<sup>3+</sup>-SrM), the magnetization value monotonically decreases while for La<sup>3+</sup> doped Sr<sub>0.7</sub>La<sub>0.3</sub>Fe<sub>12-2x</sub>Co<sub>x</sub>Al<sub>x</sub>O<sub>19</sub> (La<sup>3+</sup>-SrM) magnetization value shows a noticeable increase in magnetization value with <em>x</em>. The coercivity of the Pr<sup>3+</sup>-SrM compound was observed to decrease while that of the La<sup>3+</sup>-SrM compound showed a marked 40% increase at <em>x</em> = 0.2 (~5829 Oe) in comparison to undoped SrFe<sub>12</sub>O<sub>19</sub> (~3918 Oe). A difference in Curie temperature was also observed, with Tc ~ 525<span style="white-space:nowrap;">°</span>C at <em>x</em> = 0.4 for Pr<sup>3+</sup>-SrM and Tc = 505<span style="white-space:nowrap;">°</span>C for <em>x</em> = 0.4 for La<sup>3+</sup>-SrM compound. The observed differences in magnetic properties have been explained on the basis of the site occupancy of Co<sup>2+</sup> and Al<sup>3+</sup> in the presence of rare-earth ions. The presence of non-magnetic rare-earth ion, La<sup>3+</sup>, improved saturation magnetization, and coercivity and deemed suitable replacement for Sr<sup>2+</sup>. The hyperfine parameters namely quadrupole shift showed a decrease with the La3<sup>+</sup> or Pr<sup>3+</sup> doping independent of (Co<sup>2+</sup>-Al<sup>3+</sup>) ions doping. Overall, the Mossbauer analysis suggests that the (Co<sup>2+</sup>-Al<sup>3+</sup>) impurities prefer occupancy at 2<em>a</em> site.
基金Institute for Research & Medical Consultations(IRMC)of Imam Abdulrahman Bin Faisal University(IAU-Saudi Arabia) for supporting this study through the Projects application number: [2017-IRMC-S-3][2018-IRMC-S1]and[2018-IRMC-S-2]
文摘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.
基金the University Natural Science Fund of Jiangsu Province, China (No. 10KJB430008)the Advanced Project of the General Reserve Department of PLA for the financial support
文摘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）.
基金supported by the National Public Welfare Fund Industry Research(201410026)Scientific Research Foundation of Education Office of Sichuan Province(13Z198)the Young and Middle-aged Academic Leaders of Scientific Research Funds of Chengdu University of Information Technology(J201222)
文摘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.
基金supported by the Institute for Research&Medical Consultations(IRMC)of Imam Abdulrahman Bin Faisal University(IAU-Saudi Arabia)(2017-IRMC-S-3,2018-IRMC-S-1,2018-IRMC-S-2).
文摘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.
基金conducted with financial support from the Russian Science Foundation (Agreement No. 19-19-00694 of 06 May 2019)。
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant No.51725104)Beijing Natural Science Foundation,China(Grant No.Z180009)。
文摘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)Co_(x)Mg_(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 Ba_(0.3)Sr_(1.7)Co_(x)Mg_(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.
基金supported by the Taif University Researchers Supporting Project number(TURSP-2020/293),Taif University,Taif,Saudi Arabia。
文摘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.
基金supported by a generous grant from the Scientific Research Fund (SRF) in Jordan under grant number(S/1/21/2009)support of the German Academic Exchange Program(DAAD)the Deanship of Scientific research at the University of Jordan under contract number 1404 are also acknowledged
文摘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.
基金Project supported by the Institute for Research&Medical Consultations(Projects application No.2017-IRMC-S-3,No.2018-IRMC-S-1 and No.2018-IRMC-S-2)the Deanship of Scientific Research(Projects application No.2017-576-IRMC and No.2018-209-IRMC)of Imam Abdulrahman Bin Faisal University(Saudi Arabia).
文摘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.
文摘In this comparative study,Tb and Tm substituted Sr-hexafe rrites(HFs) with the chemical compositions of SrTb_(x)Fe_(12-x)O_(19) and SrTm_(x)Fe_(12-x)O_(19)(x=0.00,0.02 and 0.04) were fabricated via citrate sol-gel approach.The AC susceptibility and FC-ZFC magnetization were investigated.The product structure and morphologies were also investigated via XRD,TEM and SEM along with EDX.Measurements of temperature dependence of magnetization M-T and AC magnetic susceptibility versus temperature were carried out.The various synthesized HFs displayed ferrimagnetic behavior within 10-325 K.At lower temperatures,super-spin glass-like behavior was noticed.Neel-Arrhenius and Vogel-Fulcher models were employed to explore the experimental data of AC susceptibility.
基金This work was financially supported by the National Natural Science Foundation of China (No. 59995320.4).
文摘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.
文摘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）.
文摘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.
基金supported by the Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST“MISiS”(Grant No.K4-2015-040)
文摘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.
文摘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.
基金supported by the National Key Research Program of China(2022YFB3807603)the Science and Technology Projects in Guangzhou(202201000008)+2 种基金the Guangdong Provincial Key Laboratory(2020B1212060066)the National Natural Science Foundation of China(Grants Nos.52272108,and 52002134)the Hubei Provincial Natural Science Foundation of China(2023AFA105).
文摘Realizing robust magnetoelectric(ME)coupling effect near room temperature is still a long-standing challenge for the application of multiferroic materials in next-generation low-power spintronic and memory devices.Here we report a systematic study on the magnetic,dielectric,and ME coupling properties of Y-type hexaferrite Ba_(0.5)Sr_(1.5)Co_(2)Fe_(12-x)Al_(x)O_(22)(x=0.0,0.5,1.0)single crystals.The Al doping can induce the shifting of the alternating longitudinal conical(ALC)-proper screw(PS)magnetic phase transition temperature from 200 K for x?0e365 K for x-1.0.The most interesting feature is that the Ba_(0.5)Sr_(1.5)Co_(2)Fe_(11)AlO_(22) single crystal displays a direct and converse ME coupling coefficient with aH~3,100 ps/m and aE~3,900 ps/m at 250 K,respectively,due to the Al-doped enhanced stability of ALC phase.Moreover,the exchange bias also verifies the strong coupling of electric and magnetic orders.These results provide a valuable insight on the modulation of ALC structure and the mechanism of ME effect in Y-type hexaferrites.
基金the Deanship of Scientific Research at King Khalid University for funding this work through a large group Research Project under grant(RGP2/111/45)。
文摘Hexaferrites'magnetic and structural properties are highly sensitive to changes in sintering temperature and cationic replacements.We fabricated Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)hexaferrites using the sol-gel technique.We examined the phase,microstructure and magnetic aspects of the samples with respect to varying doping of rare earth dysprosium.The results show the expansion in the lattice upon incorporation of dysprosium against iron.Morphological studies confirm the uniform distribution of particles with slightly longitudinal nanoflakes in one direction.Magnetic investigations show an increase in magnetic saturation(Ms)with increasing dysprosium incorporation till optimum level is achieved for 15%doping concentration,with negligible change for maximum doping level.Furthermore,coercivity(Hc)and magnetic moment(mB)in terms of Bohr's magneton(μB)also show an increasing trend with dysprosium substitution levels.The maximum saturation magnetization of 33.355 emu/g is achieved with magnetic remanence of 18.290 emu/g,along with optimum magnetic moment of 6.249μB.In addition to the traditional magnetic parameters,magnetic anisotropy parameters were explored for the deep insights into magnetic parameters.These outcomes suggest that improved magnetic properties of Ca_(0.5)Cu_(0.5)Fe_(12-x)DyxO_(19)ferrites make it good substitute for storage devices,magnetic filters,and other magnetic applications.
