Present paper describes systematic studies of the functional BaFe12-xDIxO19 (DI = Al3+, In3+ 0.1 ≤ x ≤ 1.2) solid solutions. Correlation between the fine atomic structure and intrasublattice Fe3+ - ...O2− - Fe3+ superexchange interactions were explained using precision neutron powder diffraction and Mossbauer spectroscopy. Critical influence of the diamagnetic Al3+ and In3+ ions on electromagnetic properties in substituted Ba-hexaferrites (M-type) was discussed. Transmission spectra demonstrated a deep minimum in the frequency range 20–65 GHz due to natural ferromagnetic resonance (NFMR). Increase of the Al3+ ions concentration shifted the resonance frequency from 51 GHz to 61 GHz. Increase of the In3+ ions shifted the resonance frequency from 50.5 GHz to 27 GHz. Data of the numerical calculations and experimental results correlates well. It has been demonstrated that external magnetic fields critically influence on electromagnetic properties due to increase of magnetic anisotropy. This opens broad perspectives for practical applications.
•Control of electromagnetic properties in abnormally wide range was shown for BaFe12-xDIxO19.•Influence of the different ions on electromagnetic properties was demonstrated and explained.•Strong coupling between resonant frequency and external magnetic field was established.•Explanation was found in changes of magnetocrystalline anisotropy.
The lightly doped BaFe12−xDxO19 (D=Al3+, In3+; x=0.1 and 0.3) polycrystalline hexaferrite samples have been investigated by powder neutron diffractometry as well as by vibration sample magnetometry ...in a wide temperature range from 4K up to 740K and in magnetic field up to 14T to establish the nature of Fe3+(Al3+, In3+) – O2- - Fe3+(Al3+, In3+) indirect exchange interactions. The crystal structure features such as the ionic coordinates and lattice parameters have been defined and Rietveld refined. The Invar effect has been observed in low temperature range below 150K. It was explained by the thermal oscillation anharmonicity of ions. It is established that the ferrimagnet-paramagnet phase transition is a standard second-order one. From the macroscopic magnetization measurement the Curie temperature and ordered magnetic moment per nominal iron ion are obtained. From the microscopic diffraction measurement the magnetic moments at all the nonequivalent ionic positions and total magnetic moment per iron ion have been obtained at different temperatures down to 4K. The light diamagnetic doping mechanism and magnetic structure model are proposed. The effect of light diamagnetic doping on nature of Fe3+(Al3+, In3+) – O2- - Fe3+(Al3+, In3+) indirect exchange interactions with temperature increase is discussed.
•Crystal structure for lightly doped barium hexaferrites was investigated.•Atomic coordinates and lattice parameters were Rietveld refined.•Magnetic properties for lightly doped barium hexaferrites was investigated.•Magnetic structure for lightly doped barium hexaferrites was investigated.•Magnetic moments at different position and total moment per iron ion were defined.
The peculiarities of the fine atomic and magnetic structure, magnetic properties and microwave characteristics under Sc-substitution were investigated in Ba(Fe1-xScx)12O19 (x ≤ 0.1) solid solutions. ...Structural data was obtained using neutron powder diffraction with high resolution on atomic level and was described in the frame of standard P63/mmc Space Group. Almost linear increase of the main lattice parameters and internal stress was explained by the difference in ionic radius of Fe3+ and Sc3+. Magnetic properties were determined by VSM and discussed in terms of Mossbauer studies. The non-linear behavior of the magnetic parameters was explained by the features of Sc3+ ions distribution in the hexaferrite structure and some deviation from strict collinearity in the direction of the magnetic vector. Concentration dependence of coercivity in the concentration range x ≥ 0.05 was explained by rapid frustration of the magnetic structure (destruction of the magnetic long range ordering due to weakening of the intrasublattice exchange interaction in Fe3+-O2--Fe3+ in the first and second coordination spheres). Microwave properties were investigated using a co-axial method in the high frequency range (20–60 GHz). It has been demonstrated that the nature of electromagnetic absorption in Ba(Fe1-xScx)12O19 (x ≤ 0.1) solid solutions is caused by natural ferromagnetic resonance. A good correlation was established between the theoretical calculation of the resonant frequency and the experimental results. It opens broad prospects for practical applications of substituted hexaferrites at higher frequencies.
•Lightly-doped Ba(Fe1-xScx)12O19 (x < 0.1) ceramics were synthesized using solid state reactions.•Strong correlation between Sc3+ concentration and diamagnetic ions distribution was observed.•Control of the high frequency properties of the Ba(Fe1-xScx)12O19 (x < 0.1) ceramics was demonstrated.•Non-linear magnetic and microwave properties was explained by the features of magnetic structure.
Abstract
Indium-substituted strontium hexaferrites were prepared by the conventional solid-phase reaction method. Neutron diffraction patterns were obtained at room temperature and analyzed using the ...Rietveld methods. A linear dependence of the unit cell parameters is found. In
3+
cations are located mainly in octahedral positions of 4f
VI
and 12 k. The average crystallite size varies within 0.84–0.65 μm. With increasing substitution, the T
C
Curie temperature decreases monotonically down to ~ 520 K. ZFC and FC measurements showed a frustrated state. Upon substitution, the average and maximum sizes of ferrimagnetic clusters change in the opposite direction. The M
r
remanent magnetization decreases down to ~ 20.2 emu/g at room temperature. The M
s
spontaneous magnetization and the k
eff
effective magnetocrystalline anisotropy constant are determined. With increasing substitution, the maximum of the ε
/
real part of permittivity decreases in magnitude from ~ 3.3 to ~ 1.9 and shifts towards low frequencies from ~ 45.5 GHz to ~ 37.4 GHz. The maximum of the tg(α) dielectric loss tangent decreases from ~ 1.0 to ~ 0.7 and shifts towards low frequencies from ~ 40.6 GHz to ~ 37.3 GHz. The low-frequency maximum of the μ
/
real part of permeability decreases from ~ 1.8 to ~ 0.9 and slightly shifts towards high frequencies up to ~ 34.7 GHz. The maximum of the tg(δ) magnetic loss tangent decreases from ~ 0.7 to ~ 0.5 and shifts slightly towards low frequencies from ~ 40.5 GHz to ~ 37.7 GHz. The discussion of microwave properties is based on the saturation magnetization, natural ferromagnetic resonance and dielectric polarization types.
•The range of solid solutions of Ti-doped Ba-hexaferrites was expanded to 2.00.•Ti-doped Ba-hexaferrites BaFe12−xTixO19 magnetic state interpretation was given.•Mechanism of occupation nonequivalent ...crystallographic positions by Ti was determined.•The spin-glass component of the magnetic phase state is fixed.•The critical magnetic field of the spin-glass component disappearance was found.
Display omitted
A number of solid solutions based on BaFe12−xTixO19 M-type barium hexaferrite doped with titanium cations up to x = 2.00 were obtained using conventional ceramic technology. The phase composition, crystal structure and unit cell parameters were refined by the Rietveld method using powder X-ray diffraction data up to T = 900 K. It was found that all the compositions have a magnetoplumbite structure satisfactorily described by P63/mmc space group (No. 194). With increasing temperature and doping concentration, the unit cell parameters increase almost monotonically. The minimum volume of V ~ 696.72 Å3 was determined for the composition with x = 1.00 at T = 100 K, while the maximum value of V ~ 714.00 Å3 is observed for the composition with x = 2.00 at T = 900 K. The mechanism of occupation nonequivalent crystallographic positions with titanium cations is established. The spin-glass component of the magnetic phase state is fixed. The Tdif temperature of the difference between the ZFC-FC curves decreases with an increase in the concentration of titanium cations and the magnetic field from ~237.2 K to ~ 44.5 K, while the Tinf inflection temperature of the ZFC curve increases from ~21.0 K to ~23.8 K. With an increase in the doping concentration, both the Dav average and Dmax maximum clusters grow up to ~ 100 nm. As the magnetic field increases above the critical value, the spin-glass component disappears. For compositions with x > 1.00, the magnetization is not saturated in fields up to 6 T. Along with the formation of the spin-glass component, doping with titanium cations for barium hexaferrite lowers the TC Curie temperature down to T ~600 K. The Ms spontaneous and Mr remanent magnetizations, as well as the Bc coercivity, decrease with increasing doping concentration almost monotonically, while the latter has an inflection point at x = 1.00. The minimum values of spontaneous and remanent magnetization, as well as coercivity, are observed for the composition with x = 2.00 and amount to Ms ~17.7 emu/g, Mr ~1.9 emu/g, and Bc ~3.9 × 10−3 T, respectively. An interpretation of the magnetic state of the doped BaFe12−xTixO19 barium hexaferrite is given taking into account the mechanism of occupation nonequivalent crystallographic positions with titanium cations.
The gallium-doped pure barium hexaferrite (BaFe12-xGaxΟ19) with different concentration (x ≤ 2) was investigated by using neutron powder diffraction (NPD) carried out at various temperatures for ...studying the magnetic structures according to the crystal structure. A comparison between x-ray diffraction (XRD) and neutron powder diffraction (NPD) are investigated. Some differences between XRD and NPD were observed and explained by the hybridization of electronic shells in complex oxides. The atomic coordinates, as well as lattice parameters, are explained according to Rіetveld processed. The improve associated with the micro-strain value along with the lowering temperature can descrіbe through Rіetveld refinement. A model for the magnetic structure is proposed where the most possible factors and mechanism with the magnetic structure formation are discussed.
•The gallium-doped barium hexaferrite have been prepared by conventional solid reaction method.•Characterization by using neutron powder diffraction.•Comparison between X-ray diffraction and neutron powder diffraction.•Crystal and magnetic structure of the prepared samples were investigated.
Present paper describes variation of structure and magnetic properties in diamagnetically doped barium hexaferrites. Al3+ and In3+ diamagnetic ions were chosen for investigation of the correlation ...between the chemical composition, crystal structure, magnetic properties and microwave characteristics in BaFe12−xDIxO19 solid solutions. The changes of structure and electronic properties were investigated using neutron powder diffraction and Mossbauer spectroscopy. These data were used for discussion of the electromagnetic properties changes. It was demonstrated possibility of electromagnetic properties control in the samples. It was shown that all samples demonstrate correlation between electromagnetic properties and the level of chemical substitution. The transmission spectra of all the samples demonstrated a deep minimum in the frequency range 20–65 GHz which was associated with the natural ferromagnetic resonance (NFMR). Calculated data for electromagnetic absorption correlates well with experimental transmission spectra. External magnetic field leads to shift of the NFMR peak due to increase of magnetic anisotropy. It was concluded that the intrasublattice interactions were responsible for tailoring the magneto crystalline anisotropy and resonance parameters.
•BaFe12−xTixO19 (x ≤ 1) hexaferrites polycrystalline ceramics was investigated.•Substitution model by titanium cations was defined.•Mossbauer and Raman spectrometry was established.•The saturation ...magnetization decreasing with substitution level increasing was shown.•Dielectric constant and dielectric loss tangent values and temperature dependence were measured.
Titanium substituted BaFe12−xTixO19 (x ≤ 1) barium hexaferrites have been synthesized using the solid phase method. The phase purity and the crystal structure of the obtained solid solutions have been studied by X-ray diffraction. It was found that the unit cell parameters change a non-monotonically. The a parameter has a maximum of 5.896 Å at x = 0.25 and then it decreases almost linearly down to 5.886 Å at x = 1. The c parameter almost linearly increases from 23.216 Å up to 23.282 Å with x increasing. It has been discovered that titanium cations are located in the following positions: 4fIV tetrahedral and octahedral 4fVI and 12k ones. Results of the Mossbauer and Raman spectrometry confirm the established substitution mechanism. The homogeneous ferrimagnetic ordering is detected by magnetic measurements down to ~35 K. Below this temperature the noncollinear magnetic structure is formed as a result of Fe2+ cations change in the spin state from high to low configuration. Magnetization for all the samples is saturated at room temperature in fields of ~1 T. The saturation magnetization decreases from ~70.6 emu/g for x = 0.25 to ~56.7 emu/g for x = 1. The real part of the dielectric constant has value of ~0.2 for all the samples and gradually decreases at heating from room temperature up to ~500 K, after which it begins to increase sharply. The dielectric loss tangent has a maximum in the region of ~500 K and reaches a value of ~0.25 at a frequency of 104 Hz. With increasing the substitution level, the dielectric constant and the dielectric loss of all the samples increase.
•BaFe12-xGaxO19 (x≤1.2) hexaferrites were structurally attested.•Concentration dependence of magnetic parameters is constructed.•Concentration dependence of amplitude-frequency characteristics is ...constructed.•Frequency dependence of reflection coefficient is constructed.•Field dependence of NFR frequency is constructed.
The BaFe12-xGaxO19 (x=0.1–1.2) solid solutions of the barium hexagonal ferrite of M-type were synthesized and attested by the powder X-ray diffraction method at 300K. The unit cell parameters were refined. With increase of substitution level the parameters of unit cell monotonically decrease. These samples were investigated by the vibration magnetometry method. With increase of substitution level the magnetic parameters monotonically decrease. The concentration dependence of the TC Curie temperature as well as the MS spontaneous specific magnetization and the HC coercive force at 300K is constructed. The microwave properties of the considered samples in the external magnetic bias field were also investigated at 300K. It is shown that with increase of Ga3+ concentration from x=0.1 to x=0.6 the frequency value of the natural ferromagnetic resonance decreases in the beginning, and at further increase in concentration up to x=1.2 it increases again. With increase in Ga3+ concentration the line width of the natural ferromagnetic resonance increases that indicates the increase of frequency range where there is an intensive absorption of electromagnetic radiation. At the same time the peak amplitude of the resonant curve changes slightly. The frequency shift of the natural ferromagnetic resonance in the external magnetic bias field takes place more intensively for the samples with small Ga3+ concentration. It is shown the prospects of use of the Ga-substituted barium hexagonal ferrite as the material effectively absorbing the high-frequency electromagnetic radiation.
PDF
