Ti-substituted Barium Hexaferrite Research Articles

Improved magnetoelectric coupling of Co–Ti substituted barium hexaferrite at room temperature and related electrical investigations

This paper reports a systematic study of the electrical, multiferroic and magnetoelectric coupling properties of Co–Ti substituted Barium hexaferrites, having the chemical composition BaFe12-2xCoxTixO19 (x = 0–2.0; in steps of 0.5), synthesized using the sol gel auto-combustion method. X-ray Diffraction (XRD) studies and Rietveld refinement confirmed the successful incorporation of Co–Ti ions in the hexaferrite lattice with all the samples displaying Pb63/mmc space group single phase structure. Scanning Electron Microscope (SEM) images revealed the inhibition of crystal growth in a particular direction with Co–Ti substitution. The conduction mechanisms of the samples were analysed from the conductivity measurements and were found to follow Jonschers power law. The complex impedance spectroscopy analysis and the Cole-Cole plot fitted diagrams of the samples indicated the enhancement of bulk resistivity and grain boundary resistivity with substitution. Saturation magnetizations of the substituted samples decreased and were ascribed to the replacement of Fe ions by Co–Ti ions at different crystallographic sites. The observed reduction in anisotropy constant indicated the disturbance in the magnetic axis. The multiferroic nature of the substituted samples at room temperature was confirmed from the soft ferroelectric loops. Room temperature magnetoelectric coupling coefficient was found to be largely enhanced with substitution, achieving an exceptionally high value of 182mV/cmOe for the x = 1.5 sample. This may prove useful for potential use in emerging device applications as a single phase room temperature multiferroic material.

Исследование особенностей состава, магнитной и кристаллической структуры гексаферрита бария BaFe-=SUB=-12-x-=/SUB=-Ti-=SUB=-x-=/SUB=-O-=SUB=-19-=/SUB=-

The results of studies of the composition, crystal, and magnetic structure of Ti-substituted barium hexaferrite BaFe12 - xTixO19 (0.25<x<1.5) by Mössbauer spectroscopy, vibration magnetometry, X-ray diffraction, and synchronous thermal analysis are presented. Partial substitution of Fe3 + ions by Ti4 + ions revealed the presence of a limited heterovalent isomorphism realized according to the 2Fe3+ = Ti4+ + Fe2+ while maintaining charge balance. Using Mössbauer spectroscopy, an increase in the electron density of 3d electrons and the presence of Fe2+ in BaFe12 - xTixO19 samples with x = 1.5 were established. The limit of heterovalent isomorphic substitution is established, which is in the range 0.75 <x <1.0. Using Mössbauer spectroscopy and X-ray diffraction, the formation of titanium-containing phases at x = 1, 0, the content of which increases with increasing degree of substitution, is shown. Information is provided on the predominant distribution of substituent ions (Ti4+) in the structure of barium hexaferrite at positions 12k and 2b.

Synthesis and characterization of Mg–Ti substituted barium hexaferrite (BaMg0.6Ti0.6Fe10.8O19) derived from millscale waste for microwave application

Mg–Ti substituted barium hexaferrite (BaMg0.6Ti0.6Fe10.8O19) nanoparticles prepared by using steel millscale waste have been investigated towards the structural, magnetic and microwave properties. The samples were prepared using high-energy ball milling technique with the hematite (Fe2O3) as the raw utilized and processed from millscale waste product. The peaks with a single phase hexagonal structure of BaMg0.6Ti0.6Fe10.8O19 are identified at 1000 °C revealed from X-ray diffraction analysis. Higher saturation magnetization, Ms, with high crystallinity was observed in the sample due to the enhancement of superexchange interaction within the sample. The best maximum reflection loss of − 22.59 dB at the frequency and bandwidth of 9.42 GHz and 0.14 GHz was achieved in sample sintered at 1000 °C.

Enhancing absorption properties of Mg–Ti substituted barium hexaferrite nanocomposite through the addition of MWCNT

M-type barium ferrite with Mg–Ti substitution and MWCNT addition was synthesized using high-energy ball milling. The prepared sample was further analyzed using X-ray diffraction, field emission scanning electron microscope (FESEM), vibrating sample magnetometer and vector network analyzer. The results showed that the particle size had a wide range of distribution, and a hexagonal structure was formed in the sample. The sample was observed to have lower saturation magnetization and coercivity after Mg–Ti was substituted with MWCNT and added into the barium hexaferrite. Reflection loss was studied as a function of frequency and thickness of the sample. For Mg–Ti substituted barium hexaferrite composite with a thickness of 2.0 mm, the reflection loss peaked at −28.83 dB at a frequency of 15.57 GHz with a bandwidth of 6.43 GHz at a loss of less than −10 dB. The microwave absorption primarily resulted from magnetic losses caused by magnetization relaxation, domain wall resonance, and natural resonance. FESEM micrograph demonstrated that carbon nanotubes were attached to the external surface of the ferrite nanoparticles. The investigation of the microwave absorption indicated that with an addition of carbon nanotubes, the real and imaginary parts of permittivity and reflection loss had enhanced to −34.16 dB at a frequency of 14.19 GHz with a bandwidth of 5.72 GHz.

Microwave Absorption Properties of Ba–M Hexaferrite with High Substitution Levels of Mg–Ti in X Band

BaFe12−x Mg0.5x Ti0.5x O 19 nanoparticles were synthesized by using a modified sol–gel method. In order to investigate electromagnetic (EM) wave absorption properties of Mg–Ti-substituted barium hexaferrite nanoparticles, composites including ferrite (filler) and acrylic resin (matrix) with a weight ratio of 70:30 (ferrite/resin) were prepared. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), alternative gradient force magnetometer (AGFM), and vector network analyzer (VNA) were used to investigate the morphological, structural, magnetic, and EM wave absorption characteristics of the samples. The XRD results indicated that by the modified sol–gel synthesis method, the substituted compounds were a single-phase hexagonal ferrite for x=0 to x=5. FE-SEM images showed that the particle sizes were almost in a range of 35–50 nm. With an increase in the substitution level from x=0 to x=5, the maximum magnetization and coercivity decreased from 53.2 emu/g and 4900 Oe to 8.6 emu/g and 50 Oe, respectively. The reflection loss patterns of the samples showed that EM wave absorption was improved with an increase in the substitution levels, and the effect of substitution level on the intensity of EM wave absorption was discussed. The best reflection loss value was −55 dB obtained by the sample with x=5 in the frequency of 10.8 GHz. The results indicated that the composites containing Mg–Ti-substituted barium hexaferrite nanoparticles with high substitution levels synthesized by the modified sol–gel process can be considered as suitable EM wave absorbers in X-band applications.

Structural and magnetic properties of Co[sbnd]Ti substituted barium hexaferrite thick films

CoTi substituted M-type barium hexaferrite BaFe12-2xCoxTixO19 (0.0 ≤ x ≤ 1.0) thick films were prepared by screen printing method. X-ray diffraction analysis confirmed the formation of single phase BaFe12O19 (BaM). The preferential site occupation of Co2+ and Ti4+ ion for Fe3+ ion at five different crystallographic sites (12k, 4f1, 4f2, 2a, and 2b) was measured by Mössbauer spectroscopy. The analyses showed CoTi ions preferentially occupy 2b and 4f2 sites which were responsible for drastic decrease in magnetocrystalline anisotropy field (Ha). Magnetization (M) value found to be higher for x = 0.5. The coercivity (Hc) dropped dramatically, recording a reduction of about 95% at x = 1.0, attributed to decreased in Ha. SEM micrographs of CoTi substituted films revealed hexagonal grain structure. The magnetic properties of CoTi substituted BaM, suggests a possible candidate for microwave applications.

Ti-Substituted BaFe12O19 Single Crystal Growth and Characterization

Ti-substituted barium hexaferrite BaFe12O19 single crystals BaFe12–xTixO19 with x up to 1.3 and sizes 2–8 mm were grown by spontaneous crystallization from molten sodium carbonate flux. The distribution of Ti on different crystallographic sites was determined from single crystal X-ray diffraction data. For low Ti contents up to x = 0.8 the unit cell expands; on further increase of the Ti amount the unit cell starts to shrink. This behavior for low Ti contents is most likely due to a reduction of Fe3+ to Fe2+ for charge balance. At higher Ti concentrations, supposedly vacancies in the transition metal substructure are formed. An increasing Ti concentration results in a monotonous reduction of the Curie temperature from 452 to 251 °C and the saturation magnetization at room temperature from 64.8 to 24.8 emu/g for powder samples and from 70.0 to 60.1 emu/g for single crystals (for x up to 0.78).

Dielectric and magnetic properties of Mg–Ti substituted barium hexaferrite

Abstract Barium hexaferrites with general chemical formula BaFe 12−2 x Mg x Ti x O 19 ( x =0, 1, 1.5, 2) were synthesized by the solid state diffusion method. X-ray diffraction (XRD) confirmed the formation of single phase magnetoplumbite with large crystallite size. The lattice parameter a decreased with the increase in x , leading to the increase in X-ray density. Formation of well defined grains was observed through scanning electron microscopy (SEM). The dielectric properties were studied by impedance measurements as a function of frequency (in the range 100 Hz–10 MHz) and temperature (in the range 30 °C–345 °C). The effect of composition, frequency and temperature on the dielectric constant ( e′ ), dielectric loss (tan δ ), and conductivity ( σ ) have been explained on the basis of hopping of electrons between Fe 2+ and Fe 3+ ions. The variation of magnetization ( M ) with applied magnetic field ( H ) and temperature ( T ) were studied with a vibrating sample magnetometer (VSM). The coercivity ( H c ) and saturation magnetization ( M s ) decreased with the substitution level due to the occupancy of Ti 4+ ions at octahedral site and of Mg 2+ ions at tetrahedral site. Superparamagnetic behavior was observed in the compounds with x =1.5 and 2. Curie temperature decreased with the increase in x as some intersublattice exchange interactions strongly decreased with Mg and Ti addition.

Magnetic properties of Co–Ti substituted barium hexaferrite

This paper demonstrated the magnetic properties of Co–Ti substituted M-type hexaferrite of Ba(CoTi)xFe12–2xO19 (x=0.9–1.4), which was prepared by the solid-state reaction method. The single-phased M-type hexaferrite was obtained at 1050°C, and the samples could be sintered well at 1200°C. Co–Ti substitution reduces both saturation magnetization and coercivity of M-type hexaferrite, and gradually turns the magnetocrystalline anisotropy from uniaxial to planar within the composition range of x=0.9–1.2. When x⩾1.1, the samples have a good soft magnetic property with low coercivity and they exhibit high permeability in very high frequency range. Among them, the x=1.2 sample has the best magnetic property with both high permeability of μ′=40 and high cut-off frequency of 300MHz.

Dieletric and magnetic properties of ZnTi substituted M‐type barium hexaferrite

AbstractThe ZnTi substituted barium hexaferrite polycrystalline samples have been synthesized by solid‐state reaction method. The complex permittivity and permeability measurements are carried out on the BaFe12–2xZnxTixO19 (0.2 ≤ x ≤ 0.6) samples in the microwave frequency range of 8–13 GHz by cavity perturbation technique. The observed abnormal dielectric behavior, i.e., an increasing tendency of dielectric constant with frequency has been attributed to the mixed conduction. The effect of ZnTi substitution on the permittivity and dielectric loss has been investigated in the frequency range of 1 kHz–1 MHz as well. The increase in concentration of ZnTi dopants monotonically increases both the permittivity and the permeability in the investigated frequency ranges, which can be attributed to increased polarizability and unpinning of the domain walls, respectively.

Mössbauer and magnetic properties of Co–Ti substituted barium hexaferrite nanoparticles

Co–Ti substituted M-type hexagonal barium ferrite nanoparticles BaFe12−2xCoxTixO19 (0⩽x⩽1.0) have been prepared by a sol-gel method. Magnetic and structural properties of the powders were characterized with a Mössbauer spectroscopy, vibrating sample magnetometer, x-ray diffraction (XRD), thermogravimetry (TG), and differential thermal analysis (DTA). The decomposition of amorphous hydroxides in the dried precipitate continued until 570 °C, according to a TG-DTA analysis. The result of XRD measurements shows that the a and c lattice parameters increase with increasing x from a=5.882 and c=23.215 Å for x=0.0, to a=5.895 and c=23.295 Å for x=1.0. The Fe57 Mössbauer spectra were fitted by a least-squares technique with four subpatterns of Fe sites in the structure and corresponding to the 4f2, 4f1+2a, 12k, and 2b sites. The relative spectra areas of BaFe10CoTiO19 at 295 K were 15%, 30%, 50%, and 5% for 4f2, 4f1+2a, 12k, and 2b subspectra, respectively. The 2b site had a very large quadrupole splitting. The isomer shifts indicated that the valence states of the Fe ions were ferric. The magnetization slightly decreases and the coercivity, HC, drops dramatically from about 5014 to 228 Oe as x increases from 0.0 to 1.0. Co–Ti substituted barium hexaferrite to be controlled to reduce their coercivities with a small decrease of their magnetization.

Thermal expansion of Ti-substituted barium hexaferrite

Thermal expansion measurements in the range of 20–500 °C were carried out on both poly- and single crystalline samples of the hexagonal magnetoplumbite ferrite with composition BaTiFe11O19. The continuous scanning of the thermal expansion reveals the existence of a λ-type anomaly near the Curie temperature. In contrast to the usual observed anisotropic behavior for magnetoplumbite hexaferrites, the averaged thermal expansion coefficient for the a direction is larger than for the c direction, i.e., 12.8×10−6 and 9.5×10−6 °C−1, respectively.

Magnetic properties of Zn- and Ti-substituted barium hexaferrite

We have studied the magnetic properties of the barium hexaferrite series BaFe 12−2 x Zn x Ti x O 19 for 0⩽ x⩽2.0, by means of magnetization (SQUID), neutron diffraction and Mössbauer measurements. For x⩽0.8 we observe an increase of the low-temperature net magnetization relatively to the unsubstituted sample. For larger substitution, our studies indicate a deviation of the Fe spins from the collinear structure which leads to a decrease of the net magnetization. We have investigated to what extent and accuracy the molecular field approximation describes the observed magnetic properties for the x=0 and 0.4 samples taking into account the exchange integrals between different magnetic sublattices.

Influence of Fe2+ on microwave behaviour of M(Co, Ti)l,2 type hexaferrite

This work deals with M-type Co,Ti substituted barium hexaferrite, Ba(CoTi) x Fe 12-2x O 19 studied near the uniaxial-planar transition (x≥1,2). A single crystal state like was obtained by using textured ceramic. Our aim is to observe the effect of the divalent iron ions on the permeability curves. We have correlated the presence of Fe 2+ ions with the variation of the value of the permittivity e' at 0.1 GHz. The concentration of Fe 2+ ions has been varied by annealing the sintered materials under either reducing (N 2 ) or oxidizing (O 2 ) atmosphere. We have tried to interprete the important variations of the permeability in terms of domain wall and gyromagnetic contributions.

Optical absorption and faraday rotation of barium hexaferrite films prepared by laser ablation deposition

The Faraday rotation and optical absorption of the Co- and Ti-substituted barium hexaferrite thin films measured in the 500–2000 nm wavelength range at room temperature are presented together with the results of the Faraday rotation measurements carried out on selected samples at 80 K. The spectral dependences of the Faraday coefficient are described and interpreted using a set of optical electron transitions belonging to either cobalt or iron cations occupying the tetrahedral and/or octahedral positions in the spinel blocks of hexagonal ferrite crystal lattice.

Magneto-optical characteristics of Co, Ti-substituted barium hexaferrite films deposited by the dip-coating method

Pure and Co, Ti-substituted hexagonal barium ferrite (BaFe12O19, BaM) films were prepared by the dip-coating method from alkoxides. After repeated dipping, drying and calcining at 500°C for about 15 minutes in an oxygen atmosphere, polycrystalline films with a thickness of 1–1.8 μm on SiO2 substrates were obtained. Spectral dependencies of the Faraday rotation and the optical transmission of BaCoxTixFe12-2xO19 (0 ≤ x ≤ 0.8) films were measured in the range from 500 to 2500 nm at room temperature. The absorption coefficient did not display much structure, but specific Faraday rotation spectra of Co, Ti-ferrite films showed local maxima at 720, 1475 and 1750 nm. At those wavelengths, the magneto-optical figure of merit attains its maximum values. For comparison of the crystallization and magnetic properties, Ba(CoTi)xFe12-2xO19 (x = 0.9) powder has also been prepared by the sol-gel method.

Faraday rotation in cobalt- and titanium-substituted barium hexaferrites

Spectral dependences of the optical absorption and the Faraday rotation of Co- and Ti-substituted barium hexaferrite single crystals were measured in the 800–2400 nm wavelength region. The observed behaviour was explained by single ion contributions of paramagnetic and diamagnetic-like transitions due to cobalt ions present on tetrahedral sites.