Type Hexaferrites Research Articles

Insights into the structure and magnetic characteristics of Ho substituted Ca-Cu based Ca0.5Cu0.5Fe12-xHoxO19 hexaferrites nanoparticles

This work demonstrates a systematic attempt to explore the structure and magnetic properties of Ho3+ substituted Ca-Cu hexaferrite nanocrystals. Ca0.5Cu0.5Fe12-xHoxO19 (x = 0.00, 0.05, 0.10, 0.15, 0.20) M−type hexaferrites are synthesized via sol–gel auto combustion technique. XRD spectra is used to evaluate the phase, and substituent-induced modifications of crystallites. The lattice parameters ‘a’ and ‘c’ lies in the range (5.887–5.898) Å and (23.184–23.195) Å. The size of crystallites ranges from 55.73 to 59.41 nm. The specimen’s morphology indicates the consistent distribution of grains with Ho substitution. The coercivity of samples increased slightly from 2.85 to 3.15 kOe, as determined by vibrating sample magnetometer (VSM) loops, whereas saturation magnetization increased from 26.41 to 30.13 emu/g. The discussion also encompasses variations in anisotropy field (Ha), anisotropy parameter (B), magneto-crystalline anisotropic constant (K), and magnetic moment per formula unit mB(µB) and their effect on main magnetic parameters.

Studying the structural, magnetic, and dielectric properties of cobalt-substituted R- type hexaferrites

Studying the structural, magnetic, and dielectric properties of cobalt-substituted R- type hexaferrites

Impact of annealing temperature on the structural, magnetic and dielectric properties of BaFe12-xYxO19 (x = 0.0, 0.2, 0.4, 0.6) nanocrystalline samples

This paper presents an investigation into the structural, magnetic, and dielectric characteristics of BaFe12-xYxO19 (x = 0.0, 0.2, 0.4, 0.6) nanoparticles (NPs) produced by the sol-gel method at 800, 900, 1000, 1100 °C annealing. Rietveld refinement analysis shows that the lattice parameter ratio (c/a) lies within the range of 3.93–3.96 provides the confirmation of M type hexaferrite with space group P63/mmc. The average crystallite size for BaFe12O19 is found to decrease (53.0–23.4 nm) with increasing annealing temperature while for doped BaFe12-xYxO19 it is increased from 30.7 to 96.2 nm. The magnetization found to decrease (82–17 emu/g) with Y3+ content for 800 and 900 °C annealing. However, for 1000 and 1100 °C annealing the magnetization increases and reaches to maximum 100.2 emu/g for x = 0.2 at 1100 °C annealing. The site preference of the Fe3+ ions is responsible to change the value of magnetization. The coercivity of undoped BaFe12O19 varies from 4039 to 2028 with doping content. However, maximum coercivity 4586 Oe is found for x = 0.4 at 900 °C. The dielectric function is found to vary with annealing temperature and Y content as well. The wide range of magnetic properties (soft and hard magnetic) can be used in data storage, spintronic and microwave device applications.

Cr-doped Li-based [formula omitted]-(Beta) type hexaferrites: XRD, FTIR, XPS and dielectric evaluations for high-frequency applications

The rapid growth of electronic technology and communications have led to increase demand for high performance microwave absorbing materials. Ferrites are frequently used to absorb microwaves and protect against electromagnetic contamination. In the present study, β-type hexaferrite samples with different chemical compositions of LiFe11-xCrxO17 (x = 0.0, 0.1, 0.3, and 0.5) have been manufactured through the sol-gel auto-combustion technique. The effect of substituting Cr3+ on its structural, electrical and dielectric characteristics was examined. The XRD evaluation helped to develop a single-phase structure for all samples. The substitution of Cr3+ has changed the structural characteristics. FTIR analysis was used to investigate the vibrational properties of Cr-doped β-type hexaferrite. Two absorption bands in the infrared spectroscopy were used to indicate the tetrahedral and octahedral sites. XPS results revealed the incorporation of every metal ion related to their particular electronic states. The dielectric studies were determined in terms of frequency (1–6 GHz) and every sample behavior was described using the Maxwel-Wagner and Koop theories. Impedance analysis was utilized to study the effects of relaxation time and grain boundaries on the electrical features of the produced nanomaterials. Impedance Cole-Cole plots prove that all samples exhibit non-Debye-type multiple relaxation processes. It was observed that among all the synthesized samples, LiFe10.9Cr0.1O17 has a minimum reflection loss of −37.80 dB at 1.22 GHz. Cr-doped β-type hexaferrite results suggested using and designing hexaferrite-based nanocomposite for high-frequency absorbers in the microwave range.

Tailoring the structural, magnetic and dielectric properties in holmium doped Ca-Ba hexaferrite nanoparticles by regulating the Ca-Ba (1:1) concentration for magnetic and electric applications

This work reports the synthesis and characterizations of holmium (Ho) doped Ba-Ca hexaferrites (Ba0.5Ca0.5Fe12-xHoxO19). Structural analysis confirms the pure hexagonal phase throughout, and morphology shows the uniformly distributed hexagonal-shaped particles. The incorporation of Ho3+ ions significantly enhanced magnetic properties, as evidenced by vibrating sample magnetometry (VSM), attributed to the reconfiguration of Fe3+ ions and the reinforcement of superexchange interactions. Across all samples, magnetic hysteresis (M−H) loops exhibited a consistent hard ferrimagnetic behavior, with saturation magnetization (Ms) values varying within the range of 28.64 to 36.33 emu/g, remanent magnetization (Mr) from 16.24 to 20.68 emu/g, and coercivity (Hc) from 1.771 to 2.059 kOe, respectively. The composition with x = 0.09 demonstrated the highest Ms, Mr, and Hc values. The dielectric properties underscore the potential applications of fabricated M−type hexaferrites in microwave technology due to their low dissipation factor and ε“, pivotal for minimizing signal attenuation in crucial components such as filters and resonators. Moreover, Ho doped Ba-Ca hexaferrites present promising alternatives to magnets in electric vehicle applications, suggesting avenues for further research and optimization in this domain.

Electromagnetic radiation suppressor based on Co-Ti doped strontium lanthanum hexaferrite for Ku-Band applications

In this proposed work, we report Co-Ti doped Strontium-lanthanum M−type hexaferrites with general chemical formula, Sr0.85La0.15(CoTi)0.5Fe11O19 and Sr0.85La0.15(CoTi)0.75Fe10.5O19 prepared by citrate auto-combustion method. Complex permittivity, complex permeability and microwave absorptive properties of fabricated ferrite compositions were analysed in 12.4 to 18 GHz frequency range (Ku-Band). The XRD (X-ray diffraction) pattern of Co-Ti substituted compositions show single-phase M−type hexagonal ferrite indicating this co-substitution maintained the crystal phase structure. The grain diameter (average) decreased from 587 nm to 290 nm and 415 nm to 318 nm for ferrite samples with composition x = 0.50 and x = 0.75 respectively after 20 hours of ball-milling. The reflection loss (RL) exhibited the absorption bandwidth of more than 90 % (−10 dB) of value 2.41 GHz and 1.2 GHz for fabricated ferrites with chemical composition Sr0.85La0.15(CoTi)0.5Fe11O19 and Sr0.85La0.15(CoTi)0.75Fe10.5O19 respectively.. Both dielectric loss tangent and magnetic loss tangent contributed to enhance total loss tangent which represents microwave absorbing properties of the prepared ferrite samples. Reflection coefficient (S11) values for open circuit method also shows absorption bandwidth (−10 dB) of more than 90 % for these ferrites. Double layer electromagnetic absorber was simulated and observed improved reflection loss and absorption bandwidth. Therefore, these suggested ferrite samples have potential to be used as electromagnetic wave absorbing material of both single and double layer at higher frequency range.

Cu2+/Dy3+ dual doped calcium based Ca1-xCuxFe12-xDyxO19 hexaferrites: Microstructural and magnetic properties for magnetic applications

The structural and magnetic behaviour of hexaferrite can be significantly altered by varying the sintering temperature and cationic subtitutions. Therefore, using the sol–gel route, we have synthesized M−type Ca1-xCuxFe12-xDyxO19 (x = 0.0, 0.05, 0.10, 0.15, 0.20) hexaferrite nanoparticles in the present research work. The samples' microstructure, phase, and magnetic characteristics are examined concerning different doping concentrations using SEM, XRD, and VSM. The analysis indicates a minor percentage of Fe2O3 phases in all samples. The refined lattice variables ‘a’ and ‘c’ are initially enhanced by increasing the level of doping upto x = 0.15 and then decreases. Similarly, the average crystallite size shows an increase continuously. The remanence and saturation magnetization rise first as the doping level increases, then show a minor change for the maximum doping level. Like this, as the doping content is raised, the coercivity and magneto-crystalline anisotropy field increased first and then showed a minor decrease. The sample with the best magnetic properties is Ca0.85Cu0.15Fe11.85Dy0.15O19 with Ms = 35.738 emu/g, mB(µB) = 6.732B, Mr = 20.430 emu/g, Hc = 3.15 kOe, and Mr/Ms = 0.572. All samples were excellent candidates for use in magnetic devices due to their high Mr/Ms values. The effect of doping on the magnetic features of M−type hexa-ferrites has made them useful in numerous applications, such as high-performance self-biased circulators, magnetic filters, and storage devices.

Green synthesis of aluminium-substituted calcium hexaferrite nanoparticles for high-frequency applications

As the first of their kind, Al3＋-substituted calcium hexaferrite (CaAlxFe12−xO19 (x=0, 1, 3, 5 and 7)) nanoparticles (NPs) were synthesized via a facile, economical, eco-friendly lemon juice extract-mediated green solution combustion method. The samples were calcined, followed by characterization. The Bragg reflections confirm the formation of a single-phase magnetoplumbite (M)-type hexaferrite crystal structure. No other impurity or mixed phases are observed even after the substitution of Al3＋ in the host matrix. The crystallite size decreases from 17 to 11 nm with an increase in the substitution of Al3＋ ions. Surface morphological analysis shows the presence of agglomerated irregularly shaped NPs. The direct band gap estimated with Wood and Tauc’s relation decreases from 4.22 to 3.76 eV with an increase in the substitution of Al3＋ ions. These Al3＋-substituted calcium hexaferrite NPs are predicted to be useful in high-frequency applications based on structural, dielectric, and magnetic studies.

The influences of additives in M−type (Ba and Sr) hexaferrites’ microstructure, sintering and magnetic properties: A review

Interest in the utilization of M−type hexaferrites in magnetic applications as a substitution for rare earth minerals is rapidly growing due to the low cost and compatible magnetic properties of such materials. However, low magnetic properties and high sintering temperatures are the primary drawbacks that limit the use of SrM and BaM in various applications. Therefore, it is essential to carry out processes aimed at reducing the sintering temperature and enhancing magnetic properties beyond the threshold of 0.125 kOe coercivity, 0.5 mr/ms, and achieving higher remanence values to make them suitable for hard magnetic applications. These improvements can be achieved through synthesis techniques involving substitution and/or additives. Notably, numerous studies have been conducted on different synthesis methods and substitution techniques, and they have reached their limits. Therefore, there is a current need for comprehensive reviews and studies on the effects of additives and sintering aids. In this paper, we review investigations and studies that focus on the impact of additives, namely silica, CaO, CaCO3, Bi2O3, B2O3, CuO, and Al2O3, on the microstructure, sintering temperature, and magnetic properties of SrM and BaM hexaferrites.

Co-precipitation method followed by ultrafast sonochemical synthesis of aluminium doped M type BaFe11.4-xAlxCo0.6O19 hexaferrites for various applications

The co-precipitation method followed by Sonochemical process was used to synthesize M-type BaFe11.4-xAlxCo0.6O19 hexaferrites (x = 0.0, 0.4, 0.8, 1.2, and 1.6) with Al3+ substitutions. XRD, FTIR, UV–vis spectroscopy, VSM, SEM and LCR meter are used for the characterizations of the synthesized materials. The optical properties, magnetic properties, structural, morphological, and dielectric properties had been systematically investigated. XRD data and cell refinement study confirmed the hexagonal crystal structure of the synthesized materials that belong to space-group of P63/MMC-(No 194). The values of lattice parameters ‘a’ and ‘c’ have been reduced from their original value 5.9145 Åto 5.8446 Åand 23.239 Åto 23.1684 Åcorrespondingly with doping content. The values of ratio c/a are found within 3.9292 to 3.9641 range, which can be regarded as optimal values for M-type hexaferrites structure as mentioned in previous studies. The crystallite size-(D) and volume-(V) decreases with doping concentration. The band gap of the synthesized materials had shown decreasing trend with doping content. The values of dissipation factor, dielectric loss ε'', and dielectric constant ε', are higher at lower frequency but get smaller as frequency increases. The dissipation factor, dielectric loss ε'', and dielectric constant ε', reduced as the concentration of aluminium is increased. From the analysis of M−H loops it has been concluded that saturation magnetization and remnant magnetization is decreasing with aluminium content, while coercivity is increasing. The anisotropy parameter (B) and anisotropy field (Ha) had shown increasing trend with aluminium concentration. FTIR analysis showed the development of barium hexaferrites in two main absorption-bands, the enormous frequency-band and the low frequency-band. The position of these bands were moved towards a lower frequency range with increasing Al substitution level. The reduction in band gap as well as the enhancement in magnetic and dielectric properties of barium M type hexa-ferrites as a result of aluminium doping making them suitable for various applications, including magnetic storage media, magnetic sensors, microwave devices, electromagnetic wave absorbers and permanent magnets etc.

Electronic structure, and dielectric, magnetic and reflection-loss behaviors of BaFe12-xMnxO19 (0 < x ≤ 2) hexaferrites

M−type hexaferrites doped with transition metals are important materials used widely in modern electronic devices. Although many research works considered their magnetic properties, the relation between their electronic structure and electromagnetic behaviors have been less taken into account, particularly Mn-doped M−type hexaferrites. This work presents a detailed study on the electronic structure, and dielectric, magnetic and reflection-loss behaviors of BaFe12-xMnxO19 (x = 0.5, 1 and 2) hexaferrite specimens prepared by conventional solid-state reactions. The analysis of X-ray absorption spectra proves a mixed oxidation state of Fe2+,3+ and Mn2+,3+ ions, and chemical shifts of Fe2+ → Fe3+ and Mn2+ → Mn3+ when x increases from 0.5 to 2. These factors change the unit-cell volume, and cause Mn3+-related Jahn-Teller distortions. Concurrently, the saturation magnetization Ms varies in the range from 24 to ∼31 emu/g, which is associated with interaction competitions between Fe2+,3+-Mn2+,3+ pairs and Fe2+-related spin canting. Having studied electromagnetic behaviors, we have found strong changes in values of the permittivity and permeability at frequencies f = 10∼15 GHz. For a thickness t = 2.4 mm, reflection-loss magnitudes of microwave are about 10 ∼ 11 dB (corresponding to above 90% microwave being absorbed), with an absorption bandwidth of ∼3 GHz. Assessments of the magnetic and dielectric loss tangents, and Cole-Cole curves indicate electrical energy dissipation associated with interfacial/dipolar polarizations and conductive loss playing a dominant role in microwave absorption of BaFe12-xMnxO19.

Band–gap reduction of aluminum substituted M−type hexagonal ferrite to study its characteristics

The sol-gel auto-combustion approach was used to create a binary combination of Strontium aluminum chromium M−type hexaferrites at the iron site. The hexagonal phase and normal composition of prepared substances were confirmed through X-ray diffraction technique(XRD) and FT-IR spectroscopy. The structural investigation was evaluated using XRD, which determined crystalline size, lattice constants, miller indices, and cell volume. The production of hexaferrite is confirmed by FTIR measurement in all samples. The existence of metal-oxygen bonds on tetrahedral sites and also on octahedral confirms that all prepared samples exhibit M−type hexagonal ferrites. SEM study reveals the morphology of all prepared samples which gives the defined shape and boundary. The UV and Energy gap of all prepared samples were measured to analyze their absorption.

Cr3+ doping-controlled magnetic and dielectric properties of polycrystalline Y-type BaSrCo2Fe11-xCrxAlO22 hexaferrite

The trend towards multifunctionality and integrating electronic devices has led to the exploration of Y-type hexaferrite with excellent magnetic and dielectric properties. The Y-type hexaferrite BaSrCo2Fe11-xCrxAlO22 (0.0 ≤ x ≤ 0.5, with step of 0.1) ceramics have been prepared by conventional solid state reaction route. The phase structure, microscopic morphology, magnetic and dielectric properties of Y-type hexaferrite with chromium substitution are studied in detail. The analysis of XRD, SEM and EDS reveals that the lattice parameters and grain size decrease with the increase of Cr content. XPS results show the coexistence of Fe2+ and Fe3+. All samples exhibit well-defined ferromagnetic hysteresis loops at room temperature and the Cr3+ doping enhances the saturation magnetization and coercivity. The dielectric constants for all samples are found in the range of 10–15 and the dielectric loss is less than 0.02 at high frequency. The resistivity demonstrates that the samples possess high insulating nature with all above 2 × 109 Ω·cm, with a maximum value of 9.5 × 109 Ω·cm for x = 0.2. These results reveal that Cr3+ doped Y type hexaferrite could have potential applications in multifunctional electronic devices.

Sol–gel synthesis, electromagnetic properties and microwave absorption behavior of strontium Co2Z hexaferrites

Owing to the special planar structure and very high resistivity, [Formula: see text]-type hexaferrites possess the high initial permeability and cut-off frequency, indicating great application potential in high-frequency devices. Strontium Co2Z hexaferrites (Sr3Co2Fe[Formula: see text]O[Formula: see text]) were successfully prepared by the sol–gel method and calcined at the different temperatures from [Formula: see text]C to [Formula: see text]C. The influence of the calcined temperatures on the microstructure, phase structures, magnetic properties and microwave absorption behavior of all samples was investigated in detail. All results indicated that strontium hexaferrites go through the [Formula: see text]-, [Formula: see text]-, [Formula: see text]-, and [Formula: see text]-phase transformation process from [Formula: see text]C to [Formula: see text]C, and S-1200 (calcined at [Formula: see text]C) is confirmed to be Co2Z-type hexaferrites. S-1200 showed the highest imaginary permeability while the imaginary permittivity of all samples is close to zero, indicating the excellent microwave adsorption behavior of strontium Co2Z hexaferrites. The reflection loss results indicate that S-1200 exhibits the best microwave absorption performance with the RL value of −32.4 dB for 4.0 mm thickness at 4.72 GHz, according to the impedance matching and quarter-wavelength theory.

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

We are examining the behavior of a composite made of ferroelectrics with strong dielectric properties and ferrites with magnetic properties due to the rising need for materials for multipurpose devices. Many application avenues will be favored by the pairing of these materials’ individual qualities with one another. Perovskite and [Formula: see text]-type hexaferrite composite materials have been chosen for this study based on their magnetic and dielectric properties. The composites, (1[Formula: see text][Formula: see text]) [Formula: see text][Formula: see text]([Formula: see text][Formula: see text]Nd2[Formula: see text])4Co2[Formula: see text][Formula: see text] where [Formula: see text] = 0.52, 0.54, 0.56, 0.58 are prepared by solid state reaction method and phase formation was examined. Consideration has been given to the magnetic, dielectric, and magneto-dielectric properties. This work has established the link between the electric and magnetic domains while applying electric and magnetic forces to the materials. The magneto-dielectric research revealed magneto-electric coupling in all of the samples. However, the sample shows the maximum coupling for [Formula: see text] = 0.54 with MDR% values of 93.17%, which might be because this sample appears to have a high magneto-resistance (161%).

Enhanced magnetic properties in Sm3+ substituted SrFe12O19

M- Type hexaferrite captivates researchers and industrialists for its diverse usage and applications in different fields such as permanent magnets, storage devices, recording media, radar absorbing materials and many more. In this work, Sm3+ substituted Strontium hexaferrite, Sr1-xSmxFe12O19 (x = 0, 0.05) is synthesized by using ethylene glycol aided sol–gel auto combustion technique. X-Ray Diffraction Technique is employed for the understanding of various structural features. Phase purity of the prepared samples is authenticated by performing Rietveld refinement method. All the studied samples crystallizes in hexagonal magneto-plumbite phase with P63/mmc space group. Crystallite sizes are determined using Scherer equation. Field Emission Scanning Electron Microscopy is used for morphological analysis. Average particle size decreases with Sm3+ substitution in comparison with parent one. Both field and temperature dependent magnetization measurements are accomplished for magnetic properties analysis. Hysteresis curves show Coercivity (Hc) value increases more than two times and saturation magnetization (MS) decreases slightly as compared to parent sample which clearly indicates that the sample can be used as hard ferrites. M−T measurements are carried out with the application of 500 Oe field. Both the sample show transition around 500 °C temperature. Substituted sample also shows a prominent Hopkinson peak in comparison with parent sample.

Study of the effect of lanthanum and cerium doping combination on magnetic properties of M-type hexaferrite oxide permanent magnets

A study has been carried out on the effect of combination of Lanthanum and Cerium doping on the magnetic properties of M-Type hexaferrite permanent magnet oxide. The research was conducted using the wet mechanical milling method. The research materials used were Fe2O3, BaCO3, La2O3, and CeO2, all of which were of high purity 99.9%. This research also uses technical materials such as Ethanol and Nitrogen. Stoichiometric calculations were carried out to calculate the composition of the mixture of each ingredient. The combination of Lanthanum and Cerium substitution was varied with the composition of the doping ion concentration (x = 0 – 0.5 and y = 0 – 0.1). Permagraph characterization was carried out to determine the magnetic properties of each test sample. Results based on the permagraph characterization, the properties of M-type hexaferrite permanent magnets increased with the increase in the doping ion concentration in the sample. The presence of doping ions that have a magnetic moment is strongly suspected to contribute to the interaction of the type and the total moment in the M- type hexaferrite structure.

Magnetic field reversal of electric polarization and pressure-temperature-magnetic field magnetoelectric phase diagram of the hexaferrite Ba0.4Sr1.6Mg2Fe12O22

Pressure, as an independent thermodynamic parameter, is an effective tool to obtain novel material system and exotic physical phenomena not accessible at ambient conditions, because it profoundly modifies the charge, orbital and spin state by reducing the interatomic distance in crystal structure. However, the studies of magnetoelectricity and multiferroicity are rarely extended to high pressure dimension due to properties measured inside the high pressure vessel being a challenge. Here we reported the temperature-magnetic field-pressure magnetoelectric (ME) phase diagram of Y type hexaferrite Ba0.4Sr1.6Mg2Fe12O22 derived from static pyroelectric current measurement and dynamic magnetodielectric in diamond anvil cell and piston cylinder cell. We found that a new spin-driven ferroelectric phase emerged at P = 0.7 GPa and sequentially ME effect disappeared around P = 4.3 GPa. The external pressure may enhance easy plane anisotropy to destabilize the longitudinal conical magnetic structure with the suppression of ME coefficient. These results offer essential clues for the correlation between ME effect and magnetic structure evolution under high pressure.

Impact of BST and CCTO on the structural and dielectric study of Sm doped Y type hexaferrites

The impact of BST and CCTO on structural and dielectric study of Sm doped Y-type hexaferrite i.e. Sr2Zn2Fe12-xSmxO22, (x = 0.1) was investigated in this study. The sol-gel auto – combustion method used to synthesize the samples. XRD measurements were used to verify phase formation and spectral techniques like FTIR were utilized to track structural changes produced by Y/BST and Y/CCTO attachment. In the EDX spectra and mapping, all hosts and replaced elements are present, indicating plate like morphology. To better understand the effect of attachment, an impedance analyzer used to understand the impact of BST and CCTO on dielectric properties and obtained the necessary typical dielectric response.

Thermo-dielectric, humidito-dielectric, and humidity sensing properties of barium monoferrite and barium hexaferrite nanoparticles

Barium monoferrite and M−type hexaferrite with generic formulae BaFe2O4 and BaFe12O19 were synthesized using the sol–gel method by annealing at 1000 °C. To confirm the phase and compositions, XRD and FTIR analyses were employed, and the formation of orthorhombic crystal structure of BaFe2O4 and hexagonal crystal structure of BaFe12O19 were observed. The surface morphology of the samples was investigated through the use of the scanning electron micrograph (SEM) technique. Energy dispersive X-ray spectroscopy (EDS) confirmed the chemical compositions of the samples. At room temperature, the real part of the dielectric constant (ɛʹ), the imaginary part of the dielectric constant (ɛʹʹ), the dielectric loss tangent (tanδ), and AC conductivity (σAC) were measured at the specific frequencies (1, 1.5, and 2 MHz), and they were increased with both temperature and relative humidity (RH). Barium ferrite humidity sensors were created. The resistance of the sensor goes down as the RH% goes up, and the BaFe12O19 humidity sensor is 1.82 times more sensitive than the BaFe2O4 sensor.