M-type Barium Hexagonal Ferrite Research Articles

Investigating grain and grain boundary effects on charge transport and dielectrics in BaCoxAlxFe12-2xO19 nanoferrites

This investigation centres on the sol-gel preparation of M-type barium hexagonal ferrite (M-BaFe12O19) incorporating Co2+ and Al3+ as dopants. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were employed to assess the impact of dopants on the crystallographic structure and microstructure. The dielectric characteristics, electric modulus, impedance, and conductivity of the synthesized materials were evaluated at ambient temperature using an impedance analyzer. The structural analysis verified the presence of the hexagonal M-type crystal phase. Increasing dopant levels led to a reduction in lattice parameters, signifying unit cell shrinkage. FESEM imaging exposed the emergence of needle-shaped grains resulting from the doping process. Dielectric spectroscopy showed a decrease in both the dielectric constant (from 135.95 at x = 0.0 to 39.8) and the loss tangent (from 3.68 to 0.610) as dopant concentration increased. Conductivity exhibited relaxation at varying intervals, supported by the electric modulus spectra, which validated non-Debye relaxation behavior. Both relaxation time and AC conductivity diminished with higher dopant concentrations (from 0.000222 Ωm−1 to 0.000036 Ωm−1). The relaxation observed in conductivity and dielectric responses implies their contribution to the charge transport processes within BaCoxAlxFe12-2xO19. Electrochemical impedance spectroscopy (EIS) software was used to generate complex impedance plots, which aligned with the experimentally obtained impedance values for the synthesized compositions. Micrographs revealed a distribution of grains and grain boundaries that were consistent with calculated characteristics. This further substantiates the measured dielectric and electrical parameters.

Microstructure and gyromagnetic properties of low-sintered M-type barium hexagonal ferrite with various Ga3+ ions substitutions

The adjustment of crystal structures and properties by ion substitution has received increasing interest in recent years to solve issues related to the preparation of LTCC microwave devices. In this work, Fe3+ ions were substituted in BaFe12O19 sintered at a low temperature (920 °C). The changes in microstructures, dielectric characteristics, and magnetic properties were all examined. The ferromagnetic resonance linewidth (ΔH) of BaM ferrite was measured at magnetic fields from 6000 to 24,000 Oe. The results revealed well-grown microstructures of BaM ferrite grains at 920 °C to form typical hexagonal structures. The increase in substitution of Ga3+ ions decreased the lattice constant and cell volume of the crystals. More interestingly, the dielectric and magnetic properties depicted significant changes in the original dielectric and magnetic parameters of BaM after the substitution of Ga3+ ions. The permittivity (ε′) rose to a maximum of 16.36 at x = 0.4, while the dielectric loss angle tangent (tan δε) declined to 1.2 × 10^−3. As Ga3+ ions rose, the saturation magnetization 4πMs decreased from 3168.58 Gauss to 2571.18 Gauss. The remanence (Mr) reached a maximum value of 31.07 emu/g at x = 0.4. The ferromagnetic resonance linewidth (ΔH) of BaM ferrite sample at 31 GHz attained a minimum value of 4216.336 Oe at x = 0.8. In sum, these findings look promising for future fabrication of LTCC microwave RF devices.

Soft magnetic properties in Fe deficiency Ti–Co-doped M-type barium hexagonal ferrites

Soft magnetic properties in Fe deficiency Ti–Co-doped M-type barium hexagonal ferrites

Study of structural and magnetic properties of aluminium-substituted nanosized barium hexaferrite prepared by sol–gel auto-combustion technique

M-type nanosized barium hexaferrite BaMexFe12−xO19 (Me = Al3+ and x = 0.0, 0.4, 0.8) was synthesized by sol–gel auto-combustion method using urea as a fuel. Characterization of prepared sample was done by using different techniques, such as XRD (X-ray diffractometer), SEM (scanning electron microscope), EDAX (energy dispersive X-ray analysis), TEM (transmission electron microscope) and vibrating sample magnetometer (VSM). XRD studies show the formation of M-type barium hexagonal ferrite with space group P63/mmc. The effect of substitution of Al3+ ion for Fe3+ ion on the unit cell parameter, density, porosity has been studied. The SEM study shows that the samples exhibit spherical-shaped particles and agglomeration of individual particles in some parts. EDAX study confirms the elemental composition of prepared samples. TEM images confirm the nanosize of prepared samples. The VSM or magnetic study reveals that the saturation magnetization (Ms) value decreases from 57.1 to 33.6 emu g−1, while coercivity (Hc) value increases from 1737 to 2071 Gauss by the substitution of Al content. Substitution of Al3+ ion in barium hexaferrite significantly improves the magnetic properties.

Terahertz-infrared spectroscopy of Ti4+-doped M-type barium hexaferrite

We report on the first detailed investigations of the terahertz-infrared dielectric response of potential multiferroic single crystalline Ti-doped M-type barium hexagonal ferrite, BaFe12-xTixO19, with concentrations of the dopant above (x = 1.15) and below (x = 0.62) the critical concentration that corresponds to changes of the charge compensation mechanism. Employing terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy, we performed measurements of the spectra of complex dielectric permittivity ε*(ν) = ε′(ν)+iε"(ν) at frequencies ν = 2-8000 cm−1 (0.06–240 THz) and in the temperature interval T = 10–300 K. The effect of aliovalent cation substitution on the low-energy response of barium hexaferrite is analyzed and discussed. A rich set of polarization- and temperature-dependent excitations is observed and their origin assigned to the electronic transition within the ground state 5E of the four-fold coordinated divalent iron, to relaxational dynamics of domains, and to phonon resonances.

Effect of 200 MeV Ag16+ swift heavy ion irradiation on structural and magnetic properties of M-type barium hexaferrite

M-type barium hexagonal ferrite (BaFe12O19) has been synthesized by sol-gel auto combustion method. The synthesized material was irradiated with 200 MeV Ag16+ ions using the 15UD Pelletron tandem accelerator and the changes in structural and surface morphology of material were investigated. The pristine (as-synthesised) and irradiated samples were characterized using different experimental techniques like x-ray diffraction (XRD), Fourier-transform infrared spectroscopy, transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The strong absorption peak between 580 and 440 cm−1 in the infrared spectrum and XRD confirmed the formation of ferrite structure for both irradiated and pristine samples. XRD peaks for the irradiated barium hexagonal ferrite were slightly broadened when compared pristine ferrite samples. The crystallite size of the irradiated barium hexagonal ferrite was higher than that of pristine barium hexagonal ferrite and is consistent with TEM images. Both saturation magnetization and coercivity were decreased with irradiation.

Abstracts

M-type hexagonal ferrites have found considerable application in electronics industry as a result of tuning the electrical, dielectric and magnetic properties to match with the intended application. M-type hexagonal ferrites with improved dielectric properties are useful in high frequency application. In this research, we studied the effect of heat treatment in M-type barium hexagonal ferrites with chemical composition Ba1-xAlxFe12-yMnyO19 (x=0.6 and y=0.3) synthesized by sol-gel auto-combustion method. The prepared sample was sintered at four different temperatures (T= 750°C, 850°C, 950°C and 1050°C). The synthesized samples were characterized using X-ray diffraction (XRD), field electron scanning electron microscopy (FESEM), impedance analyser and UV-Vis spectroscopy. The band gap of the prepared sample is obtained from UV-Vis spectroscopy data. The dielectric properties were explained on the basis of Koop’s phenomenological theory and Maxwell Wagner model. The prepared sample exhibit high dielectric constant at low frequency which is typical of a ferrite material. The sample calcined at and 750°C has the highest dielectric constant at high and low frequency. Lowest dielectric loss at high frequency is observed in the sample calcinated at 1050°C while that calcinated at 850°C show the lowest loss at high frequency.

Enhanced Microwave Absorption Properties of Doped M-Type Barium Hexagonal Ferrites in Ka-band Frequencies

The present study reports the microwave absorption characteristics of La3+-Na+ substituted barium hexaferrites with chemical composition: Ba(1−2x)LaxNaxFe10CoTiO19 and Ba(1−2x)LaxNaxFe10Co0.5TiMn0.5O19 (0.00 ≤ x ≤ 0.25) respectively in Ka-band frequencies. The electromagnetic characteristics such as complex permittivity, complex permeability, and microwave absorption properties were studied using Vector Network Analyzer in 26.5–40.0 GHz frequency band. Dielectric properties showed almost constant variation with increase in frequency. Magnetic permeability spectra observed wavy variation with frequency. Comparing the electromagnetic properties of two series, it is observed that Co–Ti–Mn series observes higher values of electromagnetic properties in comparison to Co–Ti series. For composition x = 0.15 of Ba(1−2x)LaxNaxFe10Co0.5TiMn0.5O19 series, −55.33 dB reflection loss at 30 GHz frequency with −10 dB absorption bandwidth around 3.51 GHz has been observed. Thus, these materials can be employed as effective absorbers for Ka-band microwave absorbers.

Effect of calcination temperature on the structural, dielectric and optical properties of nano-sized M-type barium hexaferrites

M-type hexagonal ferrites have found considerable application in electronics industry as a result of tuning the electrical, dielectric and magnetic properties to match with the intended application. M-type hexagonal ferrites with improved dielectric properties are useful in high frequency application. In this research, we studied the effect of heat treatment in M-type barium hexagonal ferrites with chemical composition Ba1-xAlxFe12-yMnyO19 (x=0.6 and y=0.3) synthesized by sol-gel auto-combustion method. The prepared sample was sintered at four different temperatures (T= 750°C, 850°C, 950°C and 1050°C). The synthesized samples were characterized using X-ray diffraction (XRD), field electron scanning electron microscopy (FESEM), impedance analyser and UV-Vis spectroscopy. The band gap of the prepared sample is obtained from UV-Vis spectroscopy data. The dielectric properties were explained on the basis of Koop’s phenomenological theory and Maxwell Wagner model. The prepared sample exhibit high dielectric constant at low frequency which is typical of a ferrite material. The sample calcined at and 750°C has the highest dielectric constant at high and low frequency. Lowest dielectric loss at high frequency is observed in the sample calcinated at 1050°C while that calcinated at 850°C show the lowest loss at high frequency.

Magneto-optical studies of BaFe_12O_19 films grown by metallo-organic decomposition

M-type barium hexagonal ferrites BaFe12O19 (BaM) films considered for new devices that operate in the 40-70 GHz range with small or zero applied magnetic fields were characterized by magneto-optical (MO) complex polar “Kerr” effect (PKE) spectroscopy, MO magnetometry, and spectral ellipsometry (SE). The textured polycrystalline films were grown on Pt(111)/TiO2 template on Si wafer using metallo-organic decomposition technique (MOD) followed by rapid thermal annealing. In the films grown in one, two and three MOD iterations, the thickness was evaluated by SE and transmission electron microscopy. The film thickness ranged from 30 nm to 50 nm per MOD iteration. The best films display out-of-plane effective magnetic anisotropy field of 13 kOe, high perpendicular remanent magnetization and ferromagnetic resonance linewidth of 340 Oe at 60 GHz. The coercivity deduced from the MO hysteresis loops ranged between 0.25 kOe and 0.52 kOe. The SE and PKE spectra were taken at photon energies from 0.7 eV to 6.4 eV and from 1.2 eV to 4.8 eV, respectively. The PKE spectra display the structure observed on BaM single crystal natural faces normal to the c-axis. They are consistent with magnetoplumbite structure, with high degree of grain c-axis ordering, absence of foreign phases and Fe valence-exchange mechanism. Single phase nature of the films was further confirmed by grazing incidence X-ray diffraction and 57Fe nuclear magnetic resonance at 4.2 K.

Sol–gel synthesis of copper(II) and titanium(IV) ions co-doped barium ferrite submicrometer crystals and their microwave absorption performance

Copper(II)–titanium(IV)-doped barium ferrite (Ba(CuTi)xFe12−2xO19, x = 0, 0.5, 0.75, 1, 1.25) were prepared by the sol–gel method. The X-ray diffraction patterns of Ba(CuTi)xFe12−2xO19 proved that M-type barium hexagonal ferrite was formed. From the field emission scanning electron microscopy images, hexagon shaped grains could be obviously observed in Ba(CuTi)xFe12−2xO19 when x = 0.5, but its morphology tended to be irregular when x ≥ 0.75. In addition, the inductively coupled plasma atomic emission spectrometry test revealed that the doping limit of x was 0.75. Based on the electromagnetic parameters measured by the vector net-analyzer in the frequency of 2–18 GHz, the maximum reflection loss value of −37 dB at 16.7 GHz was observed for Ba(CuTi)xFe12−2xO19 (x = 0.75) with a matching thickness of 1.6 mm. Therefore, Ba(CuTi)xFe12−2xO19 may be a good candidate as the microwave absorbing material for the applications in the field of high frequency.

Sol–gel synthesis, structural and magnetic properties of nanoscale M-type barium hexaferrites BaCoxZrxFe(12−2x)O19

We have accomplished a low temperature sol–gel synthesis of nanocrystalline M-type hexaferrites BaCoxZrxFe(12−2x)O19 (x=0, 0.2, 0.4, 0.6, 0.8 and 1.0). These compounds were characterized by TGA–DTA, FT-IR, XRD, EDS and TEM. X-ray diffraction patterns demonstrate that the compounds are single phase M-type barium hexagonal ferrites (BHF) and maximum substitution is attained at x=1.0. The average size of the hexagonal platelets is 41.62nm. MS is employed to probe the magnetic properties at microscopic levels. MS studies suggest that both the nature and concentration of dopant ions control site preferences in the crystal lattice. Substitution is preferred at 4f2 and 2b sites at x=0.4, 4f1 and 4f2 sites at x=0.6 and 2a and 2b sites at x=1.0 levels. M vs H studies reveal that on substitution MS vary only slightly from 63.63 to 56.94emu/g while a drastic reduction has been observed in HC from 5428 to 630Oe. High MS and low HC values of these materials make them particularly suitable for application in data recording. Our results also show that HC can be monitored independently while retaining high saturation magnetization of BHF by making coupled substitution of divalent (Co2+) and tetravalent (Zr4+) cations for Fe3+ ions.

Physical properties of Al doped Ba hexagonal ferrite thin films

We developed the thin film microwave magnetic material, M-type barium hexagonal ferrite (BaM) doped with Al, for signal processing devices operating above 40 GHz with little to no applied magnetic field. Al was chosen as the dopant material because it significantly increases the already strong anisotropy field of BaM. A series of thin film BaAlxFe12-xO19 samples, x ranging from 0 to 2 in 0.25 steps, were deposited on Pt templates using a metal-organic decomposition growth technique. The resulting films are polycrystalline and highly textured, with the hexagonal c-axis directed out of plane. These films are also self-biasing; easy axis hysteresis loops have a high squareness ratio, s, in the 0.83-0.92 range. As expected, the anisotropy field increases with x, ranging from 1.34 to 2.19 × 106 A/m (16.9-27.5 kOe) for x = 0-2, while the saturation magnetization Ms decreases with x, ranging from 0.334 to 0.175 × 106 A/m (4πMs = 4.2-2.2 kG) for x = 0-2. These values were measured at room temperature, but the temperature dependence of these quantities was also measured below room temperature, down to 30 K. The measured ferromagnetic resonance linewidths, on the order of 12-30 × 103 A/m (140–370 Oe) for compositions below x = 1, indicate device-quality films. Above a certain threshold, the linewidth increases linearly with frequency at a rate of 0.2-0.64 × 103 (A/m)/GHz (2.5-8 Oe/GHz) for x = 0–1, respectively. The behavior of the linewidth is correlated with the structural properties of the films measured using x-ray diffraction and atomic force microscopy. The results of magnetic force microscopy, Curie point measurements, spectral ellipsometry (index of refraction), and magneto-optical measurements are also included and discussed.

Attenuated total reflection study of bulk and surface polaritons in antiferromagnets and hexagonal ferrites: Propagation at arbitrary angles

We perform a theoretical study of the reflection of infra-red radiation from antiferromagnets and M-type barium hexagonal ferrite using an attenuated total reflection (ATR) geometry. At an arbitrary angle of propagation, the electromagnetic waves in the magnetic materials cannot be separated into the usual pure transverse electric (TE) and pure transverse magnetic (TM) modes. We develop a method to solve for the ATR reflection for arbitrary angles of propagation. Using reflection maps, one can determine the dispersion relations for both bulk and surface polaritons. We find that surface polariton features in the reflection map are present at all angles for both incident TE and TM polarizations, with the exception of TM polarization when the plane of incidence is perpendicular to the applied magnetic field. We also see that the interaction of the incident electromagnetic wave with surface polaritons can cause significant transfer from TE to TM modes (and vice versa) upon reflection. When the surface modes vanish, we see that the remaining bulk mode displays reciprocal behavior.

Planar millimeter wave band-stop filters based on the excitation of confined magnetostatic waves in barium hexagonal ferrite thin film strips

A planar millimeter wave band-stop filter based on confined magnetostatic wave (MSW) excitations in an M-type barium hexagonal ferrite (BaM) film strip was demonstrated. The device consists of a BaM film strip on the top of a coplanar waveguide with the strip length along the signal line. For zero magnetic fields, the device shows a band-stop filtering response at 53 GHz. This response originates from the excitation of confined MSW modes across the BaM strip width. The filter operation frequency is tunable with low fields. This tuning relies on the change in the MSW dispersion with field.

Self-biased planar millimeter wave notch filters based on magnetostatic wave excitation in barium hexagonal ferrite thin films

The use of M-type barium hexagonal ferrite (BaM) thin films for self-biased planar millimeter wave notch filters was demonstrated for the first time. The BaM film was grown by pulsed laser deposition and showed a remanent to saturation magnetization ratio of 0.99 and a 60 GHz ferromagnetic resonance linewidth of about 300 Oe. The filter consisted of a BaM film element positioned on the top of a coplanar waveguide and showed a band-stop response at 53 GHz for zero external fields. This filtering response resulted from power absorption due to magnetostatic wave excitation in the BaM film.

Magnetic and atomic structure parameters of Sc-doped barium hexagonal ferrites

Scandium-doped M-type barium hexagonal ferrites of the composition BaFe12−xScxO19 are well suited for low frequency microwave device applications such as isolators and circulators. A series of Sc-doped M-type barium hexagonal ferrite powders (x=0–1.2) were prepared by conventional ceramic processing techniques. The resulting powders were verified to be pure phase and maintain the nominal chemical stoichiometry by x-ray diffraction and energy dispersive x-ray spectroscopy, respectively. Static magnetic measurements indicated that both saturation magnetization and uniaxial magnetocrystalline anisotropy field decreased with increasing concentration of scandium. Extended x-ray absorption fine structure measurements were carried out to clarify the correlation between the magnetic and atomic structure properties. It is found that the substituted Sc has a strong preference for the bipyramidal site. Nevertheless, the substitution did not introduce additional atomic structural disorder into the barium hexagonal structure. The structural study provided important evidence to quantitatively explain the change in dc and microwave magnetic properties due to Sc ion doping.

A study on the behaviour of M-type barium hexagonal ferrite based microwave absorbing paints

This paper deals with development of single and double-layer microwave absorbing paints using Mn-substituted barium hexagonal ferrite. The comparative studies of both theoretical and experimental results at Ku band have been reported. It has been found that the single layer absorbing paint exhibits peak absorption of 12.3 dB at 17.4 GHz for a thickness of 1.12 mm. Double layer absorbing paint with each layer of different composition of ferrite gives a broad band characteristics, but at the cost of lowered absorption.