Preparations and tailoring of structural,magnetic properties of rare earths (REs) doped nanoferrites for microwave high frequency applications

Rare earths (Res) doped Mn spinel nanoferrites with nominal composition MnR_0.2Fe_1·8O₄ (REs = Tb, Pr, Ce, Y and Gd) were synthesized using sol gel method. FTIR, XRD and FESEM were employed to evaluate the structure, phase, vibrational bands, morphology, grain size and microstructure respectively. VSM was employed to investigate the magnetic features of the Mn nanoferrite and REs doped Mn nanoferrites. XRD confirmed the single-phase cubic structure of Mn nanoferrite whereas tetragonal phase was observed for all REs doped Mn nanoferrites. Unit cell software was used to determine the structural features such as lattice parameter, cell volume, ‘da’, ‘db’, ‘dc’ and ‘dv’ respectively. FTIR results demonstrated the absorption peaks of Mn and REs doped Mn ferrite at 647-674 cm⁻¹. FESEM results depicted the irregular shapes of the particles with large agglomerations in the prepared samples. The grain size evaluated by LIM (line intercept method) found in the range of 94 to 213 nm respectively. Saturation magnetization was increased from 1.332 to 38.097 emu/g whereas remanence was increased from 1.096 to 25.379 emu/g respectively. In addition, other magnetic parameters such as initial permeability, magnetic anisotropy and magnetic moments were also increased. Moreover, Y–K angles showed significant response with REs doping in Mn ferrites. Furthermore, high frequency response and switching field distribution (SFD) of Mn ferrite and REs doped Mn ferrites were also determined. It is found that Y doped Mn ferrite depicted better high frequency and SFD response as compared to Mn ferrite and REs doped Mn ferrites. The coercivity of all these pure Mn ferrite and rare earth's substituted Mn ferrites (425–246 Oe) was higher as compared to the pure Mn and yttrium substituted Mn ferrite (107–217 Oe. Therefore, it was suggested that Y doped Mn ferrite was more suitable candidate for switching, and high frequency absorption applications in microwave regime.     

The Cobalt Zinc Spinel Ferrite Nanofiber: Lightweight and Efficient Microwave Absorber

To solve the heavy mass problem of the traditional spinel ferrite using as the microwave absorber, the Co_xZn_(1?x)Fe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) ferrite nanofibres were synthesized by electrospinning method. The phase composition, morphology, and electromagnetic properties were analyzed. The results showed that all the as‐prepared Co_xZn_(1?x)Fe₂O₄ ferrites exhibited the homogeneous nanofibrous shape. The saturation magnetization and coercivity were enhanced by tuning the Co²⁺ content. The electromagnetic loss analysis indicated that the Co_0.6Zn_0.4Fe₂O₄ ferrite nanofiber performed the strongest microwave attenuation ability. The microwave absorbing coating containing 15 wt% of Co_0.6Zn_0.4Fe₂O₄ ferrite nanofiber showed the reflection loss less than ?10 dB in the whole X‐band and 80% of the Ku‐band frequencies. Meanwhile, the surface density was only 2.4 Kg/m².     

Magnetic behavior of Ga doped yttrium iron garnet ferrite thin films deposited by sol-gel technique

Yttrium Iron Garnet (YIG) ferrites thin films having compositional formula Y₃Ga_xFe_5-xO₁₂, where (x = 0, 1, 2, 3, 4) are synthesized by sol gel dip coating technique. XRD, SEM and VSM characterizations are employed to explore structural, morphological and magnetic properties, respectively. XRD showed that Ga is completely doped in YIG and not formed any cluster or other phase with YIG. SEM confirmed the formation of agglomeration of YIG particles. Magnetic parameters like coercivity, remnant squareness, saturation magnetization, magnetic moment, anisotropy constant, initial permeability Y–K angles and microwave frequency were calculated of these films. The coercivity and moderate magnetization suggested that fabricated ferrite films are highly applicable in electromagnetic microwave absorption and frequency agile antenna for wireless communication.     

High-conducting Bi4V2−xFexO11-δ ceramics containing Fe2O3 nanocrystals: Structure and properties

The topography, structure, thermal, magnetic, and electrical properties of Bi₄V_2?xFe_xO_11-δ ceramics substituted with x = 0.5 and 0.7 Fe were studied. The microscope analysis showed the presence of iron-rich nanocrystals formed on the Bi-Fe-V-O grains. The X-ray diffraction studies confirmed that grains are built mostly of tetragonal Bi₄V_1.5Fe_0.5O_10.5 phase. Thermal properties analysis showed an order-disorder type γ ? γ? phase transition at a temperature of around 916 K, pronounced in samples doped with x = 0.5 Fe. The magnetic anomaly was observed in ceramics doped with x = 0.7 Fe which was assigned to Morin transition of Fe₂O₃. The conductivity was measured over a wide frequency range from 10 mHz to 1 MHz and at a wide temperature range from 373 to 923 K, using impedance spectroscopy. The D.C. conduction process was due to oxygen vacancies hopping while at low temperatures electron holes hopping is also possible.     

Investigation of crystal structure,dielectric properties,impedance spectroscopy and magnetic properties of (1-x)BaTiO3 – (x)Ba0.9Ca0.1 Fe12O19 multiferroic composites

Composites having composition (1-x)BaTiO₃?(x)Ba_0.9Ca_0.1Fe₁₂O₁₉ (x = 0.10, 0.20, 0.30) were synthesized by conventional solid-state reaction technique. X-ray diffraction (XRD) was used to examine the phase formation. Rietveld refinement has been done using the FullProf suite which predicted the dual phase symmetry consisting hexagonal (P63/mmc) and tetragonal (P4mm) phases in the prepared composites. The dielectric properties of the obtained composites were investigated at different temperatures as a function of frequency in the range of 100 Hz to 7 MHz. The dielectric constant increases with an increase in Ca doped barium ferrite content. The composites showed usual dielectric dispersive behaviour with increasing frequency. The conduction mechanism and dielectric relaxation were examined by complex impedance spectroscopy (CIS). Nyquist plots of all composites showed two semicircles and their centers lied below the real axis. Magnetic characterization was performed by using a vibrating sample magnetometer (VSM) up to a field of 15 kOe at room temperature. The hysteresis loops reveal the ferromagnetic nature of the composites. The values of saturation magnetization, magnetic moment per formula unit, and corresponding coercivity increases with ferrite content and are maximum at x = 0.3. AC conductivity also increases with ferrite content. The variation of frequency exponent ‘n' of the power-law with temperature suggests that the overlapping large polaron tunneling (OLPT) model is appropriate to explain the mode of conduction in all samples.     

Influence of samarium doping on magnetic and structural properties of M type Ba–Co hexaferrite

Sm doped Ba–Co hexaferrite with composition BaCo_0.8Sm_xFe_(11.2−x) O₁₉ (x=0.2, 0.4 and 0.6) were prepared via a citrate precursor method. After appropriate heat treatments, the ferrite samples were characterised by using different measurement techniques. X-ray diffraction (XRD) confirmed the formation of M phase with an average crystallite size of 35–45 nm. Observed tensile strain leads to the elongation of Ba–Co grains and was calculated using Williamson Hall plot. Surface morphology of these samples was studied by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). σ–H loops of these samples were measured at room temperature up to an applied field of 22,000 Oe using vibrating sample magnetometry (VSM). With an increase in concentration of Sm ions in Ba–Co lattice, specific saturation magnetisation (σ_s), coercivity (H_c) and retentivity (σ_r) values were found to decrease. At x=0.2, excellent values of H_c (2690.20 Oe) and squareness ratio (SQR=0.5619) were simultaneously found. These parameters make this material a promising candidate for the applications such as high density magnetic recording and enhanced memory storage.     

Influence of zinc and cadmium co-doping on optical and magnetic properties of cobalt ferrites

Zinc and cadmium based cobalt ferrites Zn_xCd_0.375-xCo_0.625Fe₂O₄ (where x = 0, 0.075, 0.125, 0.25) were successfully synthesized by a facile co-precipitation technique. Structural, optical and magnetic characteristics of the doped ferrites were systematically analyzed. X-ray Diffraction (XRD) pattern confirmed the formation of cubic spinel structure in all samples. Scanning electron microscopic analysis of surface morphology revealed cubic and spherical shaped ferrite particles. Fourier transform infrared (FTIR) spectroscopy confirmed the existence of metal oxygen (M − O) bonding in the prepared samples. Moreover, the prepared samples exhibited two frequency bands corresponding to phonon vibrational stretching in both octahedral and tetrahedral lattice positions. The optical properties were investigated in detail through photoluminescence (PL) spectroscopy and Raman spectroscopy. The PL spectrum confirmed the strong emission peaks in the ultraviolet to visible region of all the samples. Further, four active Raman modes, associated with cubic spinel structure are identified in all prepared samples. Finally, the magnetic characteristics are evaluated by using vibrating sample magnetometer (VSM) revealing ferrimagnetic and soft magnetic behavior of the samples. As the Zn and Cd co-doping in Co was increased, the H_c was decreased. The magnetic studies show the maximum H_c of 576 Oe for Cd doped cobalt ferrite, and maximum saturation magnetization (M_s) for Zn–Cd doped cobalt ferrite. It is envisaged that the newly prepared Zn–Cd co-doped cobalt ferrite would be appropriate for a number of important applications, for example, magnetic recording devices, sensors, actuators, high-density data storage devices, and biomedical equipments.     

Ammonia gas sensing and magnetic permeability of enhanced surface area and high porosity lanthanum substituted Co–Zn nano ferrites

This work reports magnetic permeability and ammonia gas sensing characteristics of La³⁺ substituted Co–Zn nano ferrites possessing chemical formula Co_0.7Zn_0.3La_xFe_2-2xO₄ (x = 0–0.1) synthesized by a sol-gel route. Refinement of X-ray diffraction (XRD) patterns of the ferrite powders by the Rietveld technique has revealed the creation of single-phase spinel structure. The tenancy of constituent cations at tetrahedral/octahedral sites was obtained from the refinement of XRD. The crystallite sizes calculated from the W–H method vary from 20 to 24 nm. The scanning electron microscope (SEM) profiles of the ferrite samples were analyzed for the morphological details. The energy dispersive X-ray analysis (EDAX) patterns of the samples were obtained to test the elemental purity of the ferrites within their stoichiometry. The transmission electron microscope (TEM) image of the ferrite (x = 0.1) exhibits the spherical and oval shaped particles with a mean size of 20 nm. Fourier transform infra-red (FTIR) spectra were analyzed to confirm the superseding of La³⁺ cations at octahedral sites. The Brunauer-Emmett-Teller (BET) analysis of nitrogen adsorption-desorption isotherms of the ferrites was performed to investigate the porous structure and to determine the surface area of the nanocrystalline ferrites. The oxidation states of the constituent ions were confirmed by means of X-ray photoelectron spectroscopy (XPS). The complex permeability as a function of frequency was studied to explore the effects of structural parameters on the magnetic behaviour of the ferrites. Analysis of gas sensing properties of the ferrites have proved that the Co–Zn–La ferrite with controlled La composition can be utilized as an effective ammonia gas sensing material in commercial gas sensors.     

Investigating the co-substitution impact of yttrium–nickel cations on lattice,morphological and magnetic parameters of SrM based ceramics

This study details the impact of the co-substitution of Y³⁺-Ni³⁺ ions for the Fe³⁺ ions on the structural, morphological and, magnetic parameters of SrM based SrY_xFe_12-2xNi_xO₁₉ (0.00 ≤ x ≥ 0.25) (SrYFeNiO) ceramic magnets synthesized by the ceramic route. Rietveld refinement of XRD confirmed the hexagonal (P63/mmc (194), z = 2) SrFe₁₂O₁₉ phase for all and an additional rhombohedral (R-3c (167), z = 6) hematite Fe₂O₃ phase for x = 0.2, x = 0.25 doping levels. The experimental and theoretical measurements abstracted the stretch of lattice parameters, i.e., the crystallographic axis and the lattice cell volume, and the dislocation of the crystallographic plane (1 1 4) for the hexagonal system, certified the heavy Y³⁺-Ni³⁺ ions substitution. To examine the morphological parameters, FESEM presented the regular hexagonal platelets of sizes ~ 1–2 μm, and EDX revealed the presence of constituent elements with their atomic and weight percentages in SrFeYNiO products. The extraction of vibrational frequencies of Fe–O bonds at tetrahedral and octahedral sites of iron through FT-IR spectroscopy authenticates the formation of the SrM phase. XPS correlated the doped elements, i.e., nickel in Ni⁺² and Ni⁺³ and yttrium in Y⁺³, whereas parent element, i.e., iron in Fe⁺³ and Fe⁺² chemical states, enlightened their impact on the magnetic parameters. Hysteresis loop analysis deduced a linear decline in magnetic parameters such as saturation magnetization (M_s) and remnant magnetization (M_r) due to non-magnetic Y³⁺ and less magnetic Ni³⁺ ions installment in 4f1 and 2b polyhedral sites of Fe³⁺ ions. However, high coercivity (H_c) up to 2.92 kOe ∈ x = 0.15 and extended magnetocrystalline anisotropy (MCA) up to 5.790× 10⁶ Erg/g ∈ x = 0.15 of our obtained ceramic magnets affirmed their application in permanent magnetic industry. M(T) curves also demonstrated the decrease in M_s and displayed an SPM at T_B, which is shifting towards lower temperatures with increasing Y³⁺-Ni³⁺ contents approved the expansion of lattice parameters.     

Dielectric relaxation and magnetic resonance in microwave absorption performance of CoxFe3-xO4 (0≤x≤1) nanocrystals

Cobalt ferrites (Co_xFe_3-xO₄, 0 ≤ x ≤ 1) may possess large magnetocrystalline anisotropy and coercivity at certain cobalt/iron (Co/Fe) ratios, while further explorations on their microwave absorption mechanisms are not adequate so far. In this study, a series of Co_xFe_3–xO₄ nanocrystals were synthesized by a developed oxidation-precipitation method, and a combination of dielectric relaxation and magnetic resonance was revealed in electromagnetic studies. Dielectric relaxation peaks were originated from orientation polarization and affected by oxygen vacancy densities. Magnetic resonance peaks were shifted to higher frequency due to the increased magnetocrystalline anisotropy at higher Co/Fe ratios. The excellent microwave absorption performance of as-prepared Co_xFe_3–xO₄ were also obtained, which should be attributed to the electromagnetic matching of dielectric relaxation and magnetic resonance at higher frequency ranges.     

Synthesis,characterization and magnetic properties of polythiophene/SrFe12-x(ZrZn)0.5xO19 nanocomposite as a microwave absorber

Ferrites are an important group of magnetic materials which are used as absorbers. The incorporation of ferrite and conducting polymer achieves great enhancement in microwave absorption properties. The nanocomposites of hexagonal ferrites embedded by conducting polymers such as polypyrrole, polyaniline and polythiophene (PTH) have been paid much attention. In the present study, strontium hexagonal ferrite doped by Zr and Zn with the final formula of SrFe_12-x(ZrZn)_0.5xO19 considering x = 0.9 and embedded by PTH was produced to achieve a nanocomposite with the highest microwave absorbing ability. In this study, after synthesis of SrFe₁₂O₁₉(ZrZn)_0.5xO19 and PTH, the nanocomposite was prepared by in situ polymerization. Wrapping the ferrite particles and PTH chains could form nanocomposite properly, and therefore acceptable interactions were observable between SrFe_12-x(ZrZn)_0.5xO19ferrite particles and PTH polymer chains in the composites. Assessing the X-ray diffraction (XRD) patterns of SrFe_12-x(ZrZn)_0.5xO19, PTH, and PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite indicated that the PTH characteristic peak shifts slightly and its peak intensity reduces, which may be attribute to the coating of PTH polymer chains onto SrFe_12-x(ZrZn)_0.5xO19 particles. We revealed also lower magnetic properties in the obtained nanocomposite. The morphological assessment also suggested that PTH could effectively coat the SrFe_12-x(ZrZn)_0.5xO19 particles. The synergistic effect of SrFe_12-x(ZrZn)_0.5xO19 particle plus PTH leads to microwave absorption percentage higher than 95% by PTH/SrFe_12-x(ZrZn)_0.5xO19 nanocomposite. Overall, nanocomposite creating by coupling interaction between SrFe_12-x(ZrZn)_0.5xO19 particles (x = 0.9) and PTH can effectively lead to achieve the highest rate of absorption of electromagnetic waves.     

Valence state of europium and samarium in Ln2Hf2O7 (Ln = Eu,Sm) based oxygen ion conductors

Ln₂(Hf_2-xLn_x)O_7-x/2 (Ln = Sm, Eu; x = 0.1) pyrochlores have been prepared via mechanical activation of oxide mixtures, followed by heat treatment for 4h at 1450 and 1600 °C, respectively. According to the ESR data, the Eu cations on the Hf site in the Hf_1-xEu_xO₆ octahedra in pyrochlore Eu₂(Hf_2-xEu_x)O_7-x/2 (x = 0.1) are most readily oxidized and reduced. Oxidation at 840 °C for 24h in air reduces the total conductivity of the Ln₂(Hf_2-xLn_x)O_7-x/2 (Ln = Sm, Eu; x = 0.1) by a factor of 2.5–6, due to the decrease in the concentrations of oxygen vacancies and Ln²⁺ ions as a result of the oxidation. The anomalous low-frequency behavior of the permittivity of the Eu₂(Hf_2-xEu_x)O_7-x/2 (x = 0.1) at ~800 °C can be understood in terms of the changes in the oxygen sublattice of the pyrochlore structure as a result of the oxidation of divalent europium and partial filling of oxygen vacancies at this temperature.     

Two phase Mg0.7Cd0.3Fe2O4–BaTiO3 composite ceramics with excellent magneto-dielectric properties for antennas in GHz band

Two phase-based composites comprising barium titanate (BaTiO₃) and spinel magnesium ferrite (1-x)Mg_0.7Cd_0.3Fe₂O₄ +xBaTiO₃ (x = 0.00, 0.03, 0.06, 0.09, and 0.12) were investigated. The phase structure revealed the coexistence of the perovskite BaTiO₃ and spinel MgFe₂O₄ phases. The microstructural analysis indicated that the average crystallite size initially increased and then decreased, as the increase in x weakened magnetisation, decreased saturation magnetisation (from 47.5 to 35.9 emu/g) and coercivity (150–0 Oe) were obtained, resulting in reduced permeability at low frequency. The permittivity gradually increased owing to tuning by barium titanate, which has strong dielectric properties, promising a relatively large miniaturisation factor. Further, low magnetic loss (tan δ_μ ∼10⁻²) and dielectric loss (tan δ_ε ∼ 10⁻² to 10⁻³) guarantee high quality factor. The low losses and enhanced dielectric properties of the as-synthesised composites could be conducive to improving the behaviour of such magneto-dielectric composite systems in microwave applications.     

Preparation,X-ray phase analysis and dielectric properties of Pb(Fe1-xCox)2/3W1/3O3 and Pb(Co1-yFey)1/2W1/2O3 (0 ≤ x,y ≤ 1) systems

In this work, the Pb(Fe_1-xCo_x)_2/3W_1/3O₃ (PFCW) and Pb(Co_1-yFe_y)_1/2W_1/2O₃ (PCFW) ceramics with 0 ≤ x, y ≤ 1 were successfully fabricated by a solid-state reaction process. X–ray diffraction phase analysis indicate the formation of two different series of solid solutions with a perovskite structure and with the substitution limits of Fe for Co (in PFCW) and Co for Fe (in PCFW) are x = 0.35 and y ≈ 0.05, respectively. Based on the results of dielectric study of the PFCW ceramics, it was shown that a crossover from relaxor ferroelectric to ferroelectric with a diffuse phase transition takes place at x = 0.10. In the case of PCFW ceramics, the observed dielectric maxima correspond to the phase transitions at 320 K and 256 K. The peculiarities of the temperature dependencies of the thermally stimulated depolarization currents of PFCW and PCFW solid solutions were studied and discussed.     

Effect of Zn substitution on the AC induction heating properties of ZnxMn1-xFe2O4 (x = 0.1–0.9) nanoparticles prepared using microwave assisted synthesis

Zn_xMn_1-xFe₂O₄ (x = 0.1–0.9) magnetic nanoparticles (MNPs) were prepared using a microwave-assisted coprecipitation method, and the effect of Zn substitution on the AC induction heating properties of the MNPs was investigated. With increasing Zn substitution, owing to the lower solubility product of Zn²⁺ ions, the formation of new nuclei was preferred over grain growth, which reduced the average crystallite size. The saturation magnetization initially increased with Zn substitution, attained the maximum value at x = 0.5, and decreased beyond that due to Yafet-Kittel type triangular spin ordering. The prepared MNPs exhibited superparamagnetic behaviour at ～ 300 K. AC induction heating studies of the MNPs indicated a specific absorption rate of ～ 130 ± 4 W/g_Fe at x = 0.1. The AC induction heating efficiency did not exhibit any non-monotonic variation at x = 0.5, and progressively decreased with increasing Zn concentration. This was attributed to the reduction in the MNP size and anisotropy energy density at higher Zn concentration that caused the relaxation dynamics to be Nèel dominated with lower effective relaxation time. AC induction heating studies on the agar-immobilized samples confirmed the Brownian relaxation mediated magneto-thermal energy conversion at lower Zn concentration. The obtained results demonstrated that saturation magnetization alone does not influence the AC induction heating efficiency and relaxation dynamics play a significant role.     

Structural,magnetic and electrical properties along with antifungal activity & adsorption ability of cobalt doped manganese ferrite nanoparticles synthesized using combustion route

Ultrafine powders of Cobalt doped manganese ferrite with elemental composition Mn_1-xCo_xFe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) were synthesized using combustion method. The formation of the pure cubic spinel phase of ferrite structure was confirmed using X-ray diffraction and Fourier transform infrared spectroscopy. Structural parameters such as lattice constant, X-ray density, mass density, porosity, and cell volume were seen to be greatly influenced by cobalt doping. The surface morphology of the nanocrystalline samples was studied using a scanning electron microscope. The particle size distribution was determined using a Transmission electron microscope and nanograins of the samples were found to have dimensions in the range 15 nm–30 nm. It also showed its dependence on the extent of cobalt inclusion. Variation of magnetization and magnetic moment as a function of magnetic field and temperature was investigated using a vibrating sample magnetometer (VSM). The parameters such as saturation magnetization ‘M_S’ and inversion temperature T_I were seen to depend upon Co⁺² concentration. The variation dielectric constant ‘Ԑ’ as a function of frequency was studied. Antifungal activity of these ferrite nanoparticles against Rhizopus fungi was also investigated at room temperature. The antifungal activity was seen to increase with increasing Co⁺² content in the manganese ferrite structure and hence cobalt doped manganese ferrites are proposed as a candidate material for industries manufacturing antifungal products. The adsorption studies were also investigated using Methylene dye as the adsorbate.     

Structural,magnetic, and electrical evaluations of rare earth Gd3+ doped in mixed Co–Mn spinel ferrite nanoparticles

The controlled and stable crystal structure, reduction in Curie temperature and semiconducting nature of oxide materials are the key factors for magnetoelectrical applications. Therefore, Co_0.6Mn_0.4Gd_xFe_2-xO₄ where x = 0, 0.033, 0.066 and 0.10 were synthesized to analyse the structural, morphological, magnetic, and electrical properties using a sol-gel autocombustion approach. The X-ray diffraction pattern reveals that the cubic crystallite size decreases with increasing smaller content of Gd³⁺ oxides without any secondary phase. Field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) study explain the complete morphology, agglomeration and dense structure of rare earth-doped Gd oxide in the mixed Co–Mn spinel ferrite nanoparticles. Fourier transform infrared spectra confirms the formation of a spinel structure with absorption bands below 1000 cm^?1. The magnetic analysis shows that the saturation magnetization (59.20 emu/g - 49.71 emu/g) and coercivity (985.21 Oe – 254.11 Oe) of the synthesized samples decreased with increasing content of Gd³⁺ ions. The increase in DC conductivity with increasing temperature verifies the semiconducting nature of the synthesized samples, and a higher DC conductivity of the Co_0.6Mn_0.4Gd_0.10Fe_1.90O₄(CMGF3) samples was observed at approximately 0.0362 S/cm at 973 K temperature.     

Y3+ composition and particle size influenced magnetic and dielectric properties of nanocrystalline Ni0.5Cu0.5YxFe2-xO4 ferrites

The rare earth Yttrium (Y³⁺) doped Ni–Cu nanoferrites (NCY ferrites) with chemical formulation, Ni_0.5Cu_0.5Y_xFe_2-xO₄ (x = 0–0.125) were prepared successfully by the sol gel route. The X-ray diffraction (XRD) of NCY ferrites revealed that a single phase of cubic spinel is created within the synthesized ferrites. The crystallite sizes obtained by XRD pattern are in the range of 51–84 nm, in good agreement with those obtained by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FSEM). The calculated lattice parameter of NCY ferrite unit cells initially decreases up to x = 0.1 and increase afterwards for x = 0.125. From FESEM and TEM micrographs, surface morphology and microstructure of NCY nanoferrites were studied. The energy dispersive X-ray spectroscopy (EDS) patterns have confirmed the stoichiometric presence of Ni, Cu, Y, O and Fe, those were used to prepare the samples. The variations in the magnetic properties with Y³⁺ compositions were investigated by obtaining the hysteresis loops of NCY ferrites. The magnetic hopping lengths L_A and L_B were calculated from XRD. The saturation magnetization, Bohr magneton number, coercivity and retentivity of the ferrites were influenced by the structural parameters like crystallite size and lattice strain. The frequency variation of dielectric constant and loss tangent exhibit space charge polarization as a phenomenon governing the dielectric behavior of the ferrites.     

Synthesis and magnetic properties of La3+-Co2+ substituted strontium ferrite particles using modified spray pyrolysis–calcination method

The purpose of the research was to improve the intrinsic magnetic properties of strontium ferrite by substituting lanthanum and cobalt for strontium and iron. The salt-assisted ultrasonic spray pyrolysis (SA-USP) following calcination process were used to from La-Co substituted strontium ferrite particles (La_xSr_1-xFe_12-yCo_yO₁₉), and their compositional dependent magnetic properties systemically investigated. All the samples were calcined at 1050 °C for 1 h in an air atmosphere to yield single-phased hexagonal particles several hundred nanometers to microns in size. A saturation magnetization of 70.76 emu/g and a coercivity 7265 Oe were obtained at a composition of La_0.25Sr_0.75Fe_11.75Co_0.25O₁₉. The amount of Co was reduced to obtain an optimized saturation magnetization of 71.40 emu/g and a coercivity of 7572 Oe at a composition of La_0.25Sr_0.75Fe_11.8Co_0.2O₁₉.     

Resistive switching effect in RE-Doped cobalt ferrite nanoparticles

Spinel ferrite along with numerous important properties, also exhibit resistive switching effect. Cerium (Ce) doped Co-ferrite nanoparticles having composition CoFe_2-xCe_xO₄ (where x = 0.0, 0.05, 0.15, 0.20) were synthesized by co-precipitation synthesis route. X-ray Diffraction analysis confirmed the formation of cubic spinel phase with minor amount of impurities. Frequency dependent dielectric and electrical properties were studied at room temperature within frequency range of 20 Hz to 3 MHz. Dielectric constant, dielectric losses and AC conductivity decreases with cerium substitutions which is usual trend observed in ferrite materials. Modified Debye function was employed to fit Dielectric constant (ε′)- frequency (f) data. Jonscher's power law was employed to study AC conductivity. DC resistivity decreased with increasing temperature. DC resistivity and drift mobility decreased with cerium substitution while activation energy increased. Current–Voltage (I–V) curves of the synthesized composition were studied at room temperature. Current–Voltage (I–V) curves showed nonlinear hysteresis loop like behavior. Current follow different values for forward and reversed applied DC voltage which confirmed that resistive switching effect exit in studied samples. Sample with Ce composition x = 0.25 exhibit larger hysteresis loop than that of other compositions. This shows that sample for Ce composition x = 0.25, can be employed for nonvolatile Resistive Random-Access Memory (ReRAM) applications. Resistive switching effect was explained by utilizing Space-charge-limited current (SCLC) conduction model and by formation of a Schottky barrier at the metal-semiconductor interface.