Ferrite Li0 Research Articles

LiTiMg ferrite substrate for circular array of circular patches under external magnetic field

circular array of eight microstrip circular patches modeled on synthesized LiTiMg ferrite substrate has been investigated under the externally applied perpendicular DC magnetic field. LiTiMg ferrite substrate has been synthesized by the Solid State Reaction Technique (SSRT). Here, we also presented a comparison of radiation pattern and some other parameters, when the antenna array is biased and unbiased. Having LiTiMg substrate with perpendicular magnetic field, we reported a reduction of side-lobes, increased directivity and better radiation power response of array. Keywords: Substituted Li ferrite; microstrip array antenna; X-band frequency range.

Analysis of Magnetic Properties of Substituted Li Ferrites

Substituted Li ferrites with chemical composition Li <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5+0.5</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> -0.5 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5-1.5</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> -0.5 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> Ti <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> Zn <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , where <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> = 0.20 and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> = 0.35, 0.45, 0.55 with additions of 0.005 Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and 0.05 MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were synthesized by ceramic method and from solutions of metallic salts and citric acid. The intrinsic and extrinsic magnetic properties were measured and are discussed from the point of view of the substituting element content as well as the grain size. The magnetic polarization, Curie temperature, saturation induction, susceptibility, and coercivity were measured and the Mossbauer spectra of certain samples have been analyzed. According to the requirements in specific applications, the properties of LiZnTi ferrite can be improved by means of proper substitution of selected ions and processing technology.

Effect of Ti4+ substitution on the hyperfine properties of Li–Sb–Ti ferrites using Mössbauer spectroscopy

Mossbauer investigations were carried out at room temperature on the ferrite system Li0.6 + 0.5tFe2.3 − 1.5tTitSb0.1O4 (0.0 ≤ t ≤ 1.0 in steps of 0.2). The effect of Ti4 + concentration on the various hyperfine interactions like Isomer shift, quadrupole splitting and internal magnetic field have been studied. The spectra exhibited well-defined Zeeman sextets at low substitution level, corresponding to the A and B sites. The sample with t = 1.0 showed paramagnetic behaviour. The results obtained have been discussed.

50 MeV Li3 + ion irradiation induced modifications in structural and magnetic properties of Ti4 + -substituted Li–Al and Li–Cr ferrites

Using 50 MeV Li3 + ion irradiation, the change induced in polycrystalline ferrites Li0.5(1 + x)Ti x Al0.1Fe2.4 − 1.5x O4 (x = 0.0 to 0.3, step–0.1)[LTAF] and Li0.5(1 + x)Ti x Cr0.1Fe2.4 − 1.5x O4 (x = 0.0 to 0.3, step–0.1; LTCF) in the electronic stopping power regime is studied. Both the systems were irradiated with the same fluence of 5 × 1013 ions/cm2. The modifications of the structural and magnetic properties are studied by means of X-ray diffraction (XRD), magnetization, 57Fe Mossbauer spectroscopy and low field a. c. susceptibility. The contrast in the role of Ti4 + in the presence of Al3 + and Cr3 + causing the formation of paramagnetic centres through Swift Heavy Ion Irradiation (SHII) induced cation rearrangement has been revealed through the comparative Mossbauer signatures of both the systems. The hyperfine interaction parameters deduced through Mossbauer spectra are also discussed before and after irradiation. The observed reduction in the saturation magnetic moment and Curie temperature after irradiation supports the partial formation of paramagnetic centres and rearrangement of cations in the lattice.

Microwave properties of some substituted LiZn ferrites

Substituted Li ferrites with chemical composition Li 0.5+0.5 t −0.5 x Fe 2.5−1.5 t −0.5 x Ti t Zn x O 4, where t=0.55 and x=0.1, 0.2, 0.3 and 0.4 with additions of 0.005 Bi 2O 3 and 0.05 MnO 2 were synthesised by a ceramic method and selected parameters such as Curie temperature T c, saturation induction B s and coercivity H c were measured and discussed. The complex permeability of prepared ferrites was measured in the frequency range of 1 MHz–1 GHz using impedance spectroscopy. The permeability spectra have shown the characteristic frequency dispersion and the contributions of relaxation and resonance effects to this dispersion are also discussed. The observed dispersion resulted from the contributions of the resonance-type of domain wall motion superimposed over the relaxation-type of wall displacements or magnetisation rotation. The detected resonance can be explained by the existence of demagnetising fields due to worse grain axis continuity.

The infrared absorption and dielectric properties of Li–Ga ferrite

The investigated compositions of the Li–Ga ferrite system Li0.5Fe2.5−xGaxO4 (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) were studied by means of infrared (IR) spectroscopy. The analysis of IR spectra indicates the presence of splitting in the absorption band due to the presence of Fe2+ ions in ferrite. The dielectric constant ɛ′, the dielectric loss ɛ″ and the loss tangent tan δ were measured at elevated temperatures ranging from room temperature up to 850 K as a function of frequency (f = 102–106 Hz) for the investigated compositions. Maximum peak in tan δ and inverse peaks in ɛ′ appeared for some samples due to the resonance phenomenon. The obtained data were discussed based on the valence exchange between (Fe3+ and Fe2+) and (Ga3+ and Ga2+), i.e. hopping mechanism.

Lithium ferrite for gas sensing applications

Abstract Microstructure and gas sensing properties of pure and samarium-substituted lithium ferrites, Li0.5SmxFe2.5−xO4 (x = 0, 0.05, 0.1 and 0.2), prepared by sol–gel self-combustion were studied. Ethanol, methanol, LPG and ammonia were used as test gases. SEM investigation evidenced that Sm ions induced microstructural changes of the Li ferrite. The finest granulation (about 100 nm) and highest porosity (44%) were observed in Li0.5Sm0.2Fe2.3O4. The gas response measurements evidenced that it depended on the working temperature and gas type. All ferrites were sensitive to alcohol (ethyl and methyl) and less sensitive to ammonia and LPG. The best responses, over 85%, were obtained at operating temperatures of 340–355 °C to ethanol and methanol vapour.

The effect on dielectric losses in lithium ferrite by cerium substitution

An extensive study of magnetic and dielectric properties has been carried out on the series of cerium substituted lithium ferrite Li0.5CexFe2.5−xO4 (x = 0.0–0.10 in step of 0.02) prepared by solid-state reaction technique. Phase analysis, microstructure and magnetic properties were studied by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer (VSM), respectively. Saturation magnetization value (Ms) decreases with substitution of cerium in lithium ferrite but the real part of dielectric constant value 3.4 × 104 obtained is maximum for the molar concentration Ce = 0.06 in Li0.5CexFe2.5−xO4. Resistivity of all samples is in the range 106–107 Ω cm measured by two-probe technique.

Size-dependent magnetic properties of ordered Li0.5Fe2.5O4 prepared by the sol-gel method

Size-dependent magnetic properties of ordered Li ferrites prepared by the sol-gel method have been studied by x-ray diffraction, vibrating-sample magnetometer, and Mössbauer spectroscopy. X-ray-diffraction patterns were analyzed using Rietveld refinement. Samples annealed below 500°C have the cubic spinel structure with a small amount of α-Fe2O3 and γ-Fe2O3. As the annealing temperature increases over 500°C, hematite and maghemite phases disappear and the single-phase spinel structure (space-group P4332) with ordered cation distribution on the octahedral site is seen. Particle sizes determined by x-ray analysis range from 37nm to 87nm, respectively, as the annealing temperature increases from 450°C to 700°C. The saturation magnetization is ∼46emu∕g for the sample annealed below 500°C and increases up to 63.3emu∕g for the sample annealed at 700°C, while the coercivity of the samples has a maximum value of 152.5Oe at 500°C. Mössbauer spectral analysis revealed that there was 29% γ-Fe2O3 in the sample annealed at 450°C. The ordered cation distribution by the local symmetry reduction of sublattice gives a reasonable interpretation about the magnetic properties of nanosize particles.

Influence of 50 MeV Li3+-ion irradiation on structural and magnetic properties of Ti4+-substituted Li0.5Al0.1Fe2.4O4

The consequences of 50MeV Li3+ ion irradiation on the structural and magnetic behaviour of polycrystalline samples of spinel ferrite system Li0.5+0.5xTixAl0.1Fe2.4−1.5xO4 are investigated by using X-ray diffraction (XRD), magnetization and 57Fe Mössbauer spectroscopy. The Mössbauer spectra exhibit central enhancement after SHI-irradiation, which is attributed to the paramagnetic centres created due to the irradiation. The reduction observed in the saturation magnetic moment after SHI-irradiation is ascribed to the partial formation of paramagnetic centres and rearrangement of the cations in the lattice corroborated by XRD and Mössbauer Loretnzian intensity analysis. The presence of amorphous phase in the irradiated samples is ruled out.

On the magnetic compensation effect of lithium‐chromium ferrites Li0.5CrxFe2.5–xO4 (0 ≤ x ≤ 1.55)

AbstractLithium‐chromium ferrites Li0.5Fe2.5–xCrxO4 (0 ≤ x ≤ 1.55) were studied using X‐ray diffraction, magnetization measurements and Mössbauer spectroscopy. X‐ray diffraction patterns show that all samples have cubic spinel structure. The temperature dependent magnetic measurements revealed that a magnetic compensation point appears at chromium concentration x = 1.05, 1.25 and 1.55. Moreover, it was observed that the Curie temperature TC decreases and approaches the compensation temperature TK as Cr3+ substitution for Fe3+ increases. The magnetization data at all concentrations are discussed in the light of Néel's molecular field model taking into account the cation distributions obtained using the analysis of Mössbauer spectra. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Thermoelectric power studies of magnesium and aluminium substituted lithium ferrites

Thermoelectric power studies of Mg and Al substituted Li ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The temperature variation of the Seebeck coefficient is also discussed. On the basis of these results, an explanation for the conduction mechanism in Mg–Al–Li mixed ferrites is suggested.

Effect of mechanical pressure and sintering temperature on the electrical properties of the rare earth ferrite Li0.6Co0.1DyxFe2.3-xO4; 0.0 x ≤ 0.2

Polycrystalline samples of mixed ferrite Li0.6Co0.1Dy x Fe2.3−x O4; 0.0 ≤ x ≤ 0.2 were prepared by the standard ceramic technique. X-ray diffraction analysis was carried out to assure the formation of the samples. The resistance was measured at different temperatures (300–800 K) as a function of frequency (200 kHz–5 MHz) for the investigated samples prepared at different sintering temperatures (1100°C ≤ T s ≤ 1250°C). It is found that this type of rare earth ferrite gives a distinguishable behavior at T s = 1200°C where the resistance of the samples at room temperature reduced to ≈90% of their values of the others sintering temperatures. The data showed also that the resistance of these samples sintered at 1100°C is changed at 100 kHz from 12 MΩ without applying pressure to 19 kΩ with 0.8 MPa. This change occurs in a reversible manner (i.e., after removing the mechanical pressure effect the resistance of the samples well return to their initial values again immediately). Thus this type of rare earth ferrite could be more applicable in several advanced electronic devices can be used as a sensor for the mechanical pressure.

Effect of Mg2+on the Magnetic Compensation of Lithium–Chromium Ferrite

Mg-substituted ferrite Li0.5Mg x Fe1.25−(2/3)x Cr1.25O4 (0 ≤ x ≤ 0.3) was studied using X-ray diffraction, Mossbauer spectroscopy and magnetic measurements. X-ray diffraction patterns show that all samples have cubic spinel structure. The temperature-dependent magnetic measurements revealed that the compensation point T K of Li0.5Fe1.25Cr1.25O4 starts to approach the Neel temperature T N as Mg2+ substitution of Fe3+ increases, until the compensation disappears at x = 0.3. This effect is investigated in relation to the cation distribution established using the Mossbauer study of this system.

Composite material with substituted Li ferrite for high-frequency applications

Magnetic composites using polymer polyvinylchloride (PVC) matrix and Li ferrite of chemical formula Li 0.525Fe 1.825Ti 0.35Zn 0.30O 4 (LTZF) with treated additions of MnO 2 and Bi 2O 3 as a magnetic filler, were prepared. The substituted Li ferrite was processed by a conventional solid state reaction and the magnetic parameters, measured on the compact sintered and composite specimens, are presented. The effect of filler quantity on magnetocomposite complex permittivity and microwave absorption has been studied in X-band frequency range.

Anomalies of internal friction of ferrimagnetic spinel Li0.5Fe2.5O4 in various structural states

The results of high-temperature (20≤T≤800°C) relaxation and magnetic investigations of ferrite Li0.5Fe2.5O4 in various structural states are given. Anomalies of internal friction caused by the occurrence of ferrimagnetic and structural (ordering type) second-order phase transitions and by vibrations of domain walls of ferrimagnetic and antiphase domains were revealed. It is shown that the 1: 3 ordering of Fe3+ and Li+ ions in the octahedral sublattice of the spinel leads to a decrease in the Curie temperature, a change in the character of the temperature dependence of the low-field magnetization, and a narrowing of the temperature range of the structural phase transition, as well to a substantial weakening of dissipation processes connected with vibrations of ferrimagnetic domain walls in the field of elastic stresses.

Synthesis of Copper and Lithium Copper Ferrites as High Magnetization Materials

The ferrite with composition Cu0.5Fe2.5O4 was heat treated in air and in reducing atmospheres to different temperatures within the solid solution region confirmed by dynamic high-temperautre x-ray characterization. The samples were quenched in oil and air, and lattice parameter, Curie temperature, and saturation magnetization measurements were completed. The magnetization measurements for these samples showed a maximum 4πMs of 0.7729 and 0.5426 T at 10 and 300 K, respectively. The cationic distribution based on the low-temperature 4πMs measurements is (Cu+0.24Fe3+0.76)A[Cu+0.26Fe3+1.74]BO4 → 4.9 µ B. X-ray-pure Cu0.5Fe2.5O4 samples were also synthesized by slow cooling from the formation temperature to 900 °C in a reducing atmosphere. A temperature–PO2 diagram for the stability of Cu0.5Fe2.5O4 under the conditions of the experiment was determined. Low-temperature 4πMs measurements did not indicate an increase in the Cu+ A site occupancy for the samples cooled to 900 °C in a reducing environment above those samples that were quenched from high temperature. Curie temperatures for all Cu0.5Fe2.5O4 samples ranged from 348 to 369 °C. Lithium additions (0.1 mol/unit formula) to copper ferrite Li0.1Cu0.4Fe2.5O4 decreased the room-temperature 4πMs values to 0.5234 T with a corresponding decrease in the 10 K measurements to 0.7047 T. From the low-temperature magnetization measurements, the distribution was (Cu+0.15Fe3+0.85)A[Cu+0.25Li+0.1Fe3+1.65]BO4 → 4.48 µ B.

Localized canting effect in Zn-substituted Ni ferrites

A model of three sublattices (A, B and B′) to describe the magnetic behavior of mixed Ni–Zn ferrites is presented. It is proposed that only sublattice B′ is affected by canting, due to the substitution of Zn 2+ ions in sublattice A. The cases where: (i) only Fe 3+ ions are found in B′, and (ii) B′ is occupied by Fe 3+ and Ni 2+ ions are considered. The two-sublattice model with canting in sublattice B is presented for comparison with cases (i) and (ii). The canting angle θ L is calculated from energetic considerations, assuming that the J ij ion-to-ion interaction energies are not modified by the substitution of Zn 2+ ions in sublattice A. The number of Bohr magnetons per molecule, n B, and the Curie temperature, T c, are predicted as a function of Zn content, z. The experimental values of n B as well as the results for T c are satisfactorily reproduced by the model described in (i). Results on Zn-substituted Li ferrite are also mentioned. It is found that additional considerations on the interactions are needed for this system, as lithium acts as a non-magnetic dilution in the octahedral sublattice.

Combustion synthesis of chromium-substituted lithium ferrites Li0.5Fe2.5−xCrxO4 (x≤2.0): Rietveld analysis and magnetic measurements

Pure and chromium-substituted lithium ferrites Li0.5Fe2.5−xCrxO4 (x≤2.0) have been made in air by self-propagating high-temperature synthesis (SHS), a combustion process involving the reaction of lithium peroxide, iron oxide, chromium oxide and iron or chromium metal powders. Reactions were performed in zero field and in an applied magnetic field of 1.1 T. Both the zero field and the applied field SHS reactions proceeded with a synthesis wave which spread out from the point of initiation. Notably the applied field synthesis waves were faster and hotter than their zero field counterparts. The products from the SHS reaction were ground and sintered at 1150°C for 2 h. Rietveld analysis of the powder X-ray data on the sintered samples showed that in all cases a cubic spinel ferrite was produced which showed a decrease in the lattice parameter with increasing Cr content. The x=0 applied field sample showed 87% superstructured and 13% disordered LiFe2.5O4 whilst the zero field sample showed 30% superstructured LiFe2.5O4 and 70% disordered LiFe2.5O4. X-ray line broadening indicated crystallites of order 70–90 nm in all samples. Electron microprobe analysis and EDAX showed that the samples were homogeneous and had the expected Fe to Cr ratios. Mössbauer and magnetic hysteresis data showed a significant change in sublattice occupancy and net magnetisation with Cr content. Coercive forces in the Cr-doped ferrites were larger than in pure compositions. Samples prepared in an applied magnetic field exhibited smaller coercivity and saturation magnetisation compared to those prepared in zero magnetic field.

Self propagating high temperature synthesis of BaFe12−xCrxO19 and Li0.5Fe2.5−xCrxO4

Thermal initiation of a mix of BaO 2 , Fe 2 O 3 , Cr 2 O 3 and iron powder in air induces a self propagating reaction with velocity 1-2 mm s –1 and the formation of predominantly BaFe 12–x Cr x O 19 . Thermal initiation of a mixture of Li 2 O 2 , Fe 2 O 3 , Cr 2 O 3 and iron powder in air also induces a propagation wave with formation of predominantly Li 0.5 Fe 2.5–x Cr x O4. Heating either product mixture to 1150-1200 °C for 2 h produces phase pure crystalline powders of BaFe 12–x Cr x O 19 and Li 0.5 Fe 2.5–x Cr x O 4 . An external 1.1 T magnetic field increased the SHS synthesis wave velocity and temperature for both hard (BaFe 12–x Cr x O 19 ) and soft ferrites (Li 0.5 Fe 2.5–x Cr x O 4 ). Materials synthesised in a magnetic field showed significant changes in H c , σ max and σ r compared to those synthesized in zero field. All the samples were characterised by X-ray powder diffraction, FTIR, VSM, EDAX/SEM and Mossbauer spectroscopy.