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This investigation is motivated by the surge of interest in materials, combining high spontaneous magnetization and pseudocapacitance at room temperature. Ferrimagnetic MnFe 2 O 4 offers benefits of high magnetization. However, the non-pseudocapacitive behavior, low capacitance and high resistance of MnFe 2 O 4 are limiting factors for its applications in magnetic pseudocapacitive devices. This investigation demonstrates that nearly ideal pseudocapacitive behavior can be achieved for MnFe 2 O 4 electrodes in Na 2 SO 4 electrolyte. High pseudocapacitance is observed in positive and negative potential ranges and two different charging mechanisms are proposed. High capacitance is achieved at a low impedance. The ability to achieve comparable and high areal capacitances in the positive and negative potential ranges facilitates the fabrication of a symmetric pseudocapacitive device, containing ferrimagnetic MnFe 2 O 4 as cathode and anode material for operation in enlarged voltage window of 1.6 V. The symmetric device shows capacitance of 0.92 F cm−2 at a current density of 3 mA cm−2. The individual electrodes and device show good cycling stability. The approach is based on the use of murexide and gallocyanine as redox-active dispersants and charge transfer mediators. The analysis of testing results provides an insight into the influence of chemical structure, charge and redox properties of the dispersants on the capacitive behavior. The ability to fabricate a pseudocapacitive device, containing two ferrimagnetic electrodes is promising for energy storage, water purification and novel applications based on magnetocapacitive effects. [ABSTRACT FROM AUTHOR]

Cobalt doping's influence on the structural, magnetic, and electronic properties of the double spinel LiFeCr 4 O 8 was systematically investigated. Rietveld refinement revealed a consistent increase in lattice parameter a and unit cell volume with cobalt incorporation. Magnetic susceptibility measurements indicated three distinct transitions: an increase in the ferrimagnetic transition temperature (T N), a decrease in the magnetostructural transition temperature (T MS), and an increase in the spin gap transition by cobalt doping. Through diffuse reflectance spectroscopy the direct optical band gap (E og) was obtained with values of 1.169 eV, 1.303 eV, 1.396 eV, and 1.230 eV for x = 0.0, 0.1, 0.2, and 0.5, respectively. The observed increase in E og with cobalt doping suggests a widening of the band gap, which could be beneficial for optoelectronic applications. By means of X-ray photoelectron spectroscopy (XPS) the core levels of Li 1s , Co 3p , Fe 3p , Cr 3p , Fe 2p , Cr 2p , and O 1s were identified. XPS valence band (VB) analysis revealed a decreasing intensity at binding energy BE = 0 eV with respect to x = 0.0. Density functional theory calculations with Hubbard U correction (DFT + U) confirmed a ferrimagnetic semiconductor behavior with a direct electronic band gap (E eg) of 1.085 eV. [ABSTRACT FROM AUTHOR]

Yttrium Iron Garnet (YIG) ferrites, characterized by their superior magnetic and dielectric attributes, are instrumental in advancing the development of microwave devices, particularly in enhancing high-frequency performance, integration, and miniaturization. This paper synthesizes YIG ferrite materials with the composition Bi 0.6 Y 1.4-x Ca 1+x Fe 4.5-x V 0.5 Ge x O 12 (x = 0.10 to 0.50, incrementing by 0.10) through the solid-state sintering method. It delves deeply into the mechanism by which Ca2+-Ge4+ ions substitution regulates the magnetic properties of BiV-YIG. The microstructural and magnetic properties of the samples were systematically tested and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), vibrating sample magnetometry (VSM), and TE106 perturbation method. At a substitution content of x = 0.50, the substitution of Ge4+ ions for the Fe3+ ions at the d-site transforms the material from ferrimagnetic to paramagnetic, and the saturation magnetization of the sample drops to 132.74 G. By calculating the ferromagnetic resonance (FMR) linewidth using the law of approach to saturation, the study elucidates the negative impact of low saturation magnetization on FMR linewidth. The mechanisms proposed in this paper provide theoretical and experimental bases for reducing the FMR linewidth of high dielectric constant Bi-substituted YIG, paving the way for developing high-dielectric, low-loss YIG ferrite materials for microwave devices. [ABSTRACT FROM AUTHOR]

We prepared ultrafine MnCo 2 O 4 particles using a facile sol–gel autocombustion method. The structural and vibrational characterizations confirmed the formation of a pure cubic spinel phase in as-synthesized MnCo 2 O 4 particles. The surface morphology analyses revealed the porous structure with an average particle size of 5 nm and uniform distribution of manganese (Mn), cobalt (Co), and oxygen (O) in the particles. We observed the presence of multiple valence states of Mn and Co, occupying both tetrahedral and octahedral sites, enhancing our insight into the material's electronic properties and structural configuration. Our magnetization studies unveiled a Curie Temperature (T C) of 185 K with ferrimagnetic ordering below T C , resulting in substantial magnetization (9.8 emu/g) and coercivity (3.46 kOe) at 2 K and weak magnetic behavior above T C. This is attributed to the finite size and surface effects. Furthermore, the incorporation of MnCo 2 O 4 nanoparticles and graphene oxide into a polyurethane foam matrix resulted in an excellent sound absorption coefficient of 90 % at 2000 Hz. This outstanding acoustic performance underscores the versatile applications of MnCo 2 O 4 nanoparticles in diverse noise mitigation applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, the ion-exchange technique in molten salts was investigated to introduce copper ions in a bioactive and ferrimagnetic devitrified glass. This approach aimed to develop a magnetic and bioactive material for oncologic bone implants, able to join the ability to promote bone bonding to hyperthermic therapy while simultaneously lowering the risk of developing post-surgery infections. The ion-exchange approach was developed in order to overcome experimental critical issues related to the influence of copper introduction as a starting reagent, during the material synthesis, on magnetite nucleation. The magnetic devitrified glass was prepared by melt and quenching route, followed by ion exchange in a mixture of molten sodium and copper nitrates, in three different Na/Cu molar ratios (20, 200, 2000). The obtained samples were analysed in terms of morphology, composition, ability to release heat, bioactivity and antibacterial properties. The results revealed that copper ion-exchange involved both sodium and calcium ions and the precipitation of few amounts of copper oxide aggregates occurred. The crystalline nature of the starting material and its ability to reach the temperature needed for hyperthermia, under exposition to an alternating magnetic field, were not affected. A bacteriostatic effect was obtained by samples with the highest copper amount and the copper doping did not affect the bioactivity of the glass ceramic. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs), which are powered by Maxwell's displacement current, have a wide range of applications, including energy harvesting and self-powered sensors. However, very little attention has been paid to the effect of the ferromagnetic medium on TENG displacement current. Herein, flexible ferrimagnetic poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF–HFP))/nickel ferrite (NiFe 2 O 4) fiber composite film based TENGs were fabricated and their performances were analysed. Highly crystalline, ferrimagnetic NiFe 2 O 4 nanofibers with high aspect ratio were prepared using electrospinning technique by systematic optimization of spinning parameters. Thereafter, the fibers were reinforced into the polymeric matrix to improve the β–phase and dielectric constant which in turn significantly enhanced the TENG performance. The β–phase enhancement in the composite films was confirmed by XRD and FTIR analysis; 77 % of the β–phase was achieved with the incorporation of NiFe 2 O 4 fiber. Morphological features were examined using SEM and AFM, which revealed more β–phase spherulite formation in the composite films. A notable increase in the dielectric properties was evidenced with the addition of NiFe 2 O 4 fibers and a maximum dielectric constant of∼26 was attained at 100 Hz. The TENG was developed using P(VDF-HFP)/NiFe 2 O 4 and nylon which generated an output voltage (V pp) and current (I pp) values of 584 V and 25 μA, respectively. Furthermore, the performance of TENG under an external magnetic field was examined, and a notable improvement in performance was observed, paving the way for the application of NiFe 2 O 4 fibers in hybrid energy harvesters and self-powered sensors. [ABSTRACT FROM AUTHOR]

We have investigated, for the first time, the hyperthermia properties, antibacterial, anticancer and antioxidant activities, as well as their toxicity, of Mn 0.25 Mg 0.25 Co 0.5 Fe 2 O 4 nanoparticles synthesized by the sol-gel auto-combustion method. X-ray diffraction results revealed a pure phase and good crystallinity of the synthesized. In addition, the Fourier transform infrared (FTIR) spectrum confirmed the formation of the crystallographic sites of the synthesized structure. In terms of morphology, scanning electron microscopy (SEM) showed that the nanoparticles were agglomerated. In addition, transmission electron microscopy (TEM) revealed that the nanoparticles had a cubic shape and a nanometric size of around 32 nm. Energy-dispersive X-ray spectroscopy (EDS) confirmed the chemical composition of the nanoparticles. With regard to magnetic properties, magnetic measurements showed almost ferrimagnetic behavior, with a saturation magnetization of 38.90 emu/g at room temperature. Hyperthermia measurements revealed relatively good heating efficiencies, with SAR value of 33W/g, good temperature rise and short time to reach magnetic hyperthermia temperature 42 °C (8 min). For biological activities the nanoparticles showed an excellent capacity to neutralize free radicals, eliminating 97% of DPPH and 95% of hydrogen peroxide. The dose of 40 mg/kg of the nanoparticles caused significant alterations in hematological and biochemical profiles. The material showed a significant effect on various bacterial strains, including Staphylococcus aureus and Bacillus subtilis. The synthesized nanoparticles also showed significant activity against various cell lines, including MCF-7 and HeLa. These results strongly suggest the promising utilization of Mn 0.25 Mg 0.25 Co 0.5 Fe 2 O 4 , in many applications as a potential candidate for magnetic-mediated hyperthermia. [ABSTRACT FROM AUTHOR]

This research is focused on designing new ceramic oxides with the spinel structure for a potential application as sensitive temperature and magnetic field sensors. In this respect, the mixtures of ferrimagnetic NiFe 2 O 4 with low-resistive Ni 0.66 Cu 0.41 Mn 1.93 O 4 semiconductor (molar coefficient α = 1 / 5 and 1 / 2) were prepared using the chemical co-precipitation technique followed by a low-temperature sintering of the cold-pressed powders. For the prepared materials, a variation of the electrical conductivity σ dc with temperature T (in the range 50 K–400 K) is quantitatively analyzed using different theoretical concepts of the charge carrier hopping transport occurring in disordered materials with strong electron-phonon interaction. It has been shown that an increase in α from 0 to 1 / 2 causes a step-like change of the dc electrical conductivity and, simultaneously, a gradual change in the magnetization M determined in the saturation state. The temperature coefficient of resistance T C R of the prepared ceramics takes the values from −0.6%/K (at 400 K) to −19.6%/K (below 100 K). The highest absolute value of the magneto-resistance coefficient M R determined at 150 K (and at magnetic field 7 T) registered for ceramic oxide with α = 1 / 2 was found to be 3.4%. [ABSTRACT FROM AUTHOR]

This research is driven by a desire to create composite films that combine the ferrimagnetic capabilities of pure and La/Nd substituted Sr 3 Co 2 Fe 24 O 41 Z-hexaferrites with the multifunctional features of ferroelectric polymers. A flexible magnetoelectric (ME) polymer composite films, with Sr 3 Co 2 Fe 24 O 41 (SF), Sr 2.85 La 0.15 Co 2 Fe 24 O 41 (SF–La) and Sr 2.85 Nd 0.15 Co 2 Fe 24 O 41 (SF-Nd) as the ferrimagnetic material and poly vinylidene fluoride-hexafluoropropylene (PH) as a ferroelectric component, were synthesized using solution casting method. In the current case, two steps have been used to synthesize ferroelectric and ferrimagnetic composites films: first, SF, SF-La and SF-Nd hexaferrite samples were synthesized using solid state reaction method and then 20% weight percentage of these hexaferrites were incorporated into the PH matrix using solution casting method to form composite film. In order to find the traces of collaborative interactions between the two phases, the structural, magnetic, and ferroelectric properties of these composite samples have been studied. The XRD data confirm the formation of SF, SF-La and SF-Nd hexaferrite dispersed in a piezoelectric copolymer PH matrix. The changes in the ferroelectric properties in different magnetic fields demonstrated the existence of ME coupling in the composite films. The inclusion of PH enhanced the magnetoelectric coupling of composite films. The maximal value of magnetoelectric coupling coefficient (α ME) observed is 0.213, 1.227, 3.403 and 9.797 mV cm−1 Oe−1 for SF, PHSF, PHSF-La and PHSF-Nd, respectively. There is approximately 46-time increase in the maximum value of magnetoelectric coupling coefficient (α ME) in PHSF-Nd (9.797 mV/cm.Oe) composites as compare to pure SF (0.213 mV/cm.Oe). [ABSTRACT FROM AUTHOR]

Fe doped Sr 2 RuMnO 6 (SRMO) double perovskites (Sr 2 RuMn 1-x Fe x O 6 , x = 0, 0.1, 0.2 and 0.3) were prepared by solid-state route. Both x-ray diffraction and Raman spectroscopy were performed to investigate the crystal structure of the synthesized double perovskites. Rietveld refinement of the x-ray diffraction patterns confirmed a phase transition from tetragonal to cubic space group as a function of doping concentration of iron. Raman spectroscopy at room temperature and group theory analysis revealed the phonon modes associated with the space group of the samples. The temperature dependent Raman spectroscopy showed an anharmonic behaviour of the phonon modes of the Fe doped SRMO samples. The temperature evolution of the phononic modes in the range of 300 K–620 K is predominantly influenced by the lattice degrees of freedom. The presence of several oxidation states Mn (2+, 3+ and 4+) and Fe (3+ and 4+) was confirmed by an X-ray photoemission spectroscopy analysis of the highest doped sample (x = 0.3). The magnetic properties measurements showed that the samples were completely paramagnetic at room temperature. The samples exhibit antiferromagnetism at very low temperatures and we conclude that they exhibit ferrimagnetic ground state in the mid temperature region. [ABSTRACT FROM AUTHOR]

Samples with inversion parameter values (δ) ranging from 0.27 to 0.14 while maintaining the crystallite size value have been successfully fabricated from commercially available powders by mechanical grinding and thermal annealing treatments at temperatures ranging between 400 and 600 °C. Detailed characterization studies of these samples using X-ray, neutron diffraction and magnetic measurements have confirmed for the first time the simultaneous coexistence at 2 K of short range antiferromagnetic and ferrimagnetic ordering for a wide range of the inversion parameter. The magnetic phase diagram obtained is different from the one previously reported, which shows at 2 K the coexistence of long range antiferromagnetic order and short range order for values of inversion parameters less than 0.1 and the presence of a ferrimagnetic order only for values of δ > 0.2. At room temperature, the Rietveld analysis of NPD patterns and the magnetization curves showed a paramagnetic behavior in the samples with δ ≤ 0.1. For the samples with higher cationic inversion, typical hysteresis curves of ferrimagnetic materials were observed and the saturation magnetization values obtained agree quite well with the net magnetic moment obtained from the Rietveld refinement of the neutron diffraction patterns. [ABSTRACT FROM AUTHOR]

In the present work, [Co (1-(x + y)) Mg x Ni y ][Cr 2 ]O 4 (CMNCr)(where, x = y = 0, 0.10, 0.20) NPs are examine in detail by using experimental results. Solution combustion method is adopted to prepare the CMNCr NPs. Experimental results were studied to understand structure (using XRD), microstructure (using SEM) and magnetic behaviour (using SQUID). The structural analysis was confirmed a single-phase spinel cubic structure with singular structural distortions associated with Mg–Ni doping and the generation of metal vacancies. SEM micrographs of all samples reveal their highly porous nature. EDS was utilized to examine the elemental analysis of the samples. The formation of spinel cubic structure without impurity were also confirmed by Fourier-transform infrared (FTIR) spectroscopy and the same tool is used to investigate the absorption bands related to the A-site and B-site. For all samples, paramagnetic phase to ferrimagnetic phase transition observed at T C and conical spiral spin order transition observed at T S. The curie temperature is found to be 98 K, 89 K, and 85 K for [Co][Cr 2 ]O 4 , [Co 0.8 Mg 0.1 Ni 0.1 ][Cr 2 ]O 4 and [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 samples, respectively. The spiral transition temperature is found to be 26 K, 14 K and 8 K for [Co][Cr 2 ]O 4 , [Co 0.8 Mg 0.1 Ni 0.1 ][Cr 2 ]O 4 and [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 samples, respectively. All of the samples exhibit paramagnetic behaviour above T C. The negative magnetization effect were observed in [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 NPs. 20% of Mg and 20% of Ni substitution to Co site in [Co][Cr 2 ]O 4 leads to the evident magnetization reversal at the compensation temperature with an applied magnetic field of 100 Oe. The M − H loop at 10 K exhibits large coercivity due to the spiral spin ordering. This phenomenon of negative magnetization in the material results in a stable state of magnetization in the material, which has significant applications in the field of magnetic storage devices. [ABSTRACT FROM AUTHOR]

Copper-containing ferrimagnetic glass-ceramic with the following composition: 24.7% SiO 2 -8.5% CaO-13.5% Na 2 O-3.3% P 2 O 5 -31% Fe 2 O 3 -14% FeO–5CuO (wt%) was synthesized by means melt and quenching process both in powder and bulk form. The obtained samples were characterized and compared by means morphological, compositional and structural analyses. The magnetic properties and the ability to release heat were also investigated together with the antimicrobial properties towards S. aureus strain. The obtained results showed that copper introduction and the annealing process influenced the nucleation of crystalline phases; in particular the samples produced in powder form evidenced a low amount of magnetite and thus a reduced hysteresis area and ability to produce heat when exposed to an alternating magnetic field. While Cu-containing samples in the bulk form maintained the magnetic and calorimetric properties of pristine glass-ceramic. Preliminary evaluation of antibacterial properties demonstrated Cu-doped samples were not able to reduce the bacterial proliferation and thus the need to optimize the copper introduction process. [ABSTRACT FROM AUTHOR]

Structural, magnetic, and optical properties along with N 2 absorption-desorption features of Sm3+–Dy3+ ions co-substituted BaSr hexaferrite microspheres (HFMSs) engineered through a hydrothermal gel approach were investigated. The microstructural and morphological features were examined by powder X-ray diffraction (XRD), surface area and pore size distribution (BET), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), and transmission electron microscopy (TEM) techniques. Rietveld analysis proved the purity of products. The BET revealed a slight variation in textural characteristics with increasing Sm3+–Dy3+ substitution. The surface area (11–16 m2/g) exhibits a pore volume of ~0.07 cm3/g and average pore size distributions of 26.6 nm. The 300 K and 10 K field-dependent hysteresis loops were registered. Remanent magnetizations (M r) and coercive fields (H C) are in a range of 29.15–34.05 emu/g and 1420–5391 Oe at 300 K, respectively. The estimated saturation magnetizations (M s) vary between 53.22 emu/g and 71.08 emu/g, and magneton numbers (n B) are in a range of 10.51–13.93 μ B. At 10 K, the M r = 35.18–46.83 emu/g, H C = 1487–4760 Oe, M s = 81.82–99.17 emu/g, and n B = 14.83–19.44 μ B , which are greatly higher compared to room temperature. All magnetic parameters exhibit strong ferrimagnetic features of pristine Sr 0 · 5 Ba 0 · 5 Fe 12 O 19 and Dy3+ and Sm3+ co-doped HFMSs at both temperatures. Squareness ratios (SQRs), which are very close to 0.50 assign the single domain uniaxially symmetric structured HFMSs. δ M type of remanence plots was applied to specify the intensity and type of interparticle interactions as a function of the externally magnetic field, H. The Schuster-Kubelka-Munk theory provides to estimate direct energy band gaps (E g). Undoped or co-doped HFMSs have a very narrow magnitude of E g data between 1.795 and 1.865 eV depending on the couple ion concentrations. [ABSTRACT FROM AUTHOR]

The physical properties of the double perovskite A 2 BB'O 6 are closely related to the B-site cationic arrangement, which directly affects the crystal morphology, magnetic coupling and electronic structure. Herein, the impact of B-site antisite defects on the magnetic and electronic properties of double perovskite Pb 2 FeOsO 6 has been investigated using spin-polarized first-principles calculations. Our calculations demonstrate that B-site ordered Pb 2 FeOsO 6 is a ferrimagnetic semiconductor with the saturated magnetic moment of ~2.27 μ B f.u.−1, mainly generated from B-site Fe and B′-site Os antiferromagnetic coupling. With the introduction of B-site antisite defects, the crystal lattices nearly maintain the original structure of the ordered Pb 2 FeOsO 6 , although the internal atomic arrangements are reconstructed. Nevertheless, the saturated magnetic moment is sharply reduced in Fe/Os disordered configurations, which originates from the additional Os–Os and Fe–Fe antiferromagnetic coupling, and consequently induces Os–Os, Os–Fe and Fe–Fe spins interaction competition. Further electronic structure analyses indicate that the B-site antisite defects do not alter the semiconducting performance of Pb 2 FeOsO 6. Our study sharpens the understanding of the effects of cationic ordering on the physical properties of double perovskites and provides an alternative avenue for tailoring their characteristics. This work illustrates the nonnegligible effect of B-site atomic disorder on the atomic distribution, spin interaction arrangements and electronic transport properties in double perovskite Pb 2 FeOsO 6. Image 1 [ABSTRACT FROM AUTHOR]

A mixed-spin (5/2, 3/2) Ising model is established to describe the antiferroelectric/ferroelectric (AFE/FE) BiFeO 3 /Co bilayer structure. We study the effects of the crystal field, exchange coupling and external longitudinal electric field on the dielectric properties of the bilayer based on Monte Carlo simulation. We illustrate the temperature dependence of polarization, susceptibility, internal energy and specific heat of the system in detail. As well, we depict the phase diagram and point out the rule of the blocking temperature with various parameters. In particular, we find rich and interesting multi-cycle electric hysteresis behaviors. The results show that these parameters play a crucial part in the physical properties of the AFE/FE BiFeO 3 /Co bilayer structure. [ABSTRACT FROM AUTHOR]

We prepared pure-phase Ni x Mn 1-x Co 2 O 4 (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni x Mn 1-x Co 2 O 4 increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni 0.5 Mn 0.5 Co 2 O 4 sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni x Mn 1-x Co 2 O 4 (x = 0 and 0.25), and as the concentration of Ni increases, Ni x Mn 1-x Co 2 O 4 (x = 0.75 and 1) show a spin glass state. The structure of Ni x Mn 1-x Co 2 O 4 (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni x Mn 1-x Co 2 O 4 and that the strength of the Ni-O bond is greater than that of the Mn-O bond. [ABSTRACT FROM AUTHOR]

A detailed study has been carried out of the static and dynamic magnetic properties of ferrimagnetic spinel MgFe 1.2 Ga 0.8 O 4 nanoparticles (NPs), including the measurements of low-field dc -magnetization M (T) under zero-field-cooled (ZFC) and field-cooled (FC) conditions and ac -susceptibility χ ac (T) at different frequencies (f) and amplitudes of the ac -field (H ac). Below, a Curie temperature (T C), a clear magnetic irreversibility (M ZFC (T) ≠ M FC (T)), as well as a broad peak in both M ZFC (T)– M FC (T) magnetizations have been observed. At T ≪ T C , the two distinct, frequency-dependent peaks at T p1 ≈ 9 K and T p2 ≈ 14 K in the imaginary part of the ac -susceptibility χ ac '' (T) have been found. Their positions have been consistent with those of the anomalies detected on the temperature dependence of the magnetic contribution to the heat capacity C mag (T), and a sharp decrease of the M ZFC (T) magnetization near ≈ 10–20 K. It was revealed that the fitting of the frequency dependence of the peaks' positions (T p1 (f) and T p2 (f)) in the imaginary part of ac -susceptibility χ ac '' (T) using the Neel-Arrhenius law yields unphysical values of the relaxation time (τ 0) and, therefore, these results ruled out a possibility of an existence of superparamagnetic (SPM) clusters in the system. On the other hand, the T p1 (f) and T p2 (f) dependences followed both the Vogel-Fulcher law and the power law. These observations indicate that, a complex magnetic state in MgFe 1.2 Ga 0.8 O 4 , realized in the low temperature region, may likely be related to a progressive freezing of magnetic clusters. [ABSTRACT FROM AUTHOR]

Di-phase 0.66BaTiO 3 –0.33Co 0.8 Zn 0.2 Fe 2 O 4 ceramic composites with randomly mixed phases have been obtained by conventional sintering method (CM) and Spark Plasma Sintering (SPS). The impact of sintering method on the structural, microstructural and functional properties is comparatively analysed. The dielectric properties are dominated by the BaTiO 3 phase, with contributions from the interfaces mostly on the dielectric relaxation properties, while the ferrimagnetic character of the composite is derived from the ferrite phase as a sum property. Both CM and SPS ceramics show bi-tunable character, i.e. their permittivity can be modified by the application of both electric and magnetic fields. A high dielectric nonlinearity is mostly characteristic to the ceramics with larger grains. The electrical tunability tends to reduce by the application of a magnetic field an almost is cancelled in the SPS ceramic. The two types of ceramics show opposite signs of their magnetocapacitance properties, indicating that they have different origins. A microwave filter realised with these two types of ceramics have been tested. With increasing magnetic field from 0 to 1.9 kOe (above the magnetic coercive field), the resonance frequency can be up/down shifted, as result of the positive/negative magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

Terbium (Tb) and Thulium (Tm) co-doped strontium hexaferrites (SHFs), with composition SrFe 12-2x Tb x Tm x O 19 (0.00 ≤ x ≤ 0.04), were prepared via sol-gel auto-combustion method. The effect of Tb3+ and Tm3+ (as co-dopants) on SHFs were investigated in detail. XRD pattern of the prepared SHFs revealed the formation of M-type SHFs. A secondary phase of Fe 2 O 3 starts to appear for x ≥ 0.02. The optical band gaps (E g) of the prepared SHFs were widened with the increase in doping levels. Mössbauer study showed that the Tm3+ and Tb3+ ions have the preference to occupy 12k and 2a octahedral sites. M(H) measurements were recorded at room temperature (RT; T = 300 K) and low temperature (T = 10 K). The hysteresis loops of various SHFs revealed their ferrimagnetic (FM) nature at both RT and 10 K. Magnetic parameters including saturation magnetization (M s), remanence (M r), coercivity (H c), squareness ratio (SQR = M r /M s) and magnetic moment ( n B ) were determined. Compared to the pristine (undoped) sample, lower content of Tm3+ and Tb3+ co-substitution (x = 0.01) improves significantly the magnetic properties of SHFs. With further increasing co-substitution contents (x > 0.01), an impurity phase appears and as a result the magnetization reduces. The observed SQR values of the proposed SHFs above 0.5 clearly indicated their single domain character with uniaxial magnetocrystalline anisotropy. Our systematic synthesis strategy and characterization may constitute a basis for achieving high quality co-doped SHFs in a customized way. [ABSTRACT FROM AUTHOR]

Here, we report structural and magnetic phase transitions in NiCr 1.9 Fe 0.1 O 4 nanoparticles of size ∼60 nm synthesized through cost-effective co-precipitation route. X-ray diffraction pattern shows a stable cubic phase at RT in contrast to tetragonal phase in bulk NiCr 2 O 4. Decreasing the temperature, a complete tetragonal symmetry is observed at 50 K, while a coexistence of cubic and tetragonal phases in the intermediate temperature range. Interestingly, no tetragonal to orthorhombic phase transformation has been observed down to 12 K as observed in NiCr 2 O 4 at 70 K. The local structure examined from temperature dependent EXAFS demonstrates that although no change in distribution of cations among tetrahedral (A) and octahedral (B) sites down to 10 K has been observed, Fe3+ ions occupy A site replacing equivalent amount of Ni2+ towards B site which is contradicting to the bulk NiCr 2 O 4 where Ni2+ occupies only A site. Magnetic studies demonstrate a two-fold increase in para to long-range ferrimagnetic transition, T C , due to increase in A-B exchange interaction and no change in spiral ordering temperature, T S indicates strong B-B interaction. In addition, these nanoparticles exhibit unusually high spontaneous exchange bias of ∼1.265 kOe at 60 K. We discuss the temperature dependent exchange bias on the basis of competition between uncompensated B site moments and ferromagnetically ordered spins at A site. The tunable exchange bias without field highlight the potential applications of these materials in spintronics devices. [ABSTRACT FROM AUTHOR]

Abstract Magnesium and calcium co-substituted Ba M-type nanohexaferrite (NHFs) is fabricated via sol-gel auto-combustion technique. The phase formation was proved by XRD powder pattern, FESEM and HR-TEM. Magnetic properties of Ba 1-2x Ca x Mg x Fe 12 O 19 (x ≤ 0.1) NHFs investigated by Mossbauer Spectroscopy. The variations in line width, quadrupole splitting, isomer shift, the cation distribution of Ca2+ and Mg2+ ions and hyperfine magnetic field values were estimated. The AC magnetic susceptibility and ZFC-FC measurements were also performed for the Ba 1-2x Ca x Mg x Fe 12 O 19 (x = 0.02 and 0.08) NHFs. The M FC -M ZFC results do not show blocking temperature peak, indicating the ferrimagnetic (FM) behavior of prepared products. Different models including Neel-Arhenius (N-A), Vogel-Fulcher (V-F) and critical slowing down (CSD) were tested to evaluate the AC-magnetic susceptibility behaviors. It is demonstrated that the magnetic interactions are important for x = 0.02 NHFs. [ABSTRACT FROM AUTHOR]

Abstract Exchange bias behaviors up to room temperature have been observed in NiCo 2 O 4 /NiO nanoparticle system. The field-cooled magnetic hysteresis loops exhibit shifts both in the field and magnetization axes simultaneously. The variation of exchange bias field and magnetization shift depends strongly on the measuring temperature. In addition, the dependence of exchange bias effect on measuring temperature is not monotonous, which is reflected in the different tendency during the decrease process of magnetization shift and exchange bias field. The exchange bias field is decreased firstly at the range of 10–50 K followed by an increase of 50–200 K and decreased again of 200–320 K. By analyzing various magnetic measurements, the special exchange bias effect in NiCo 2 O 4 /NiO can be owing to the spin glass state and the ferrimagnetic/antiferromagnetic coupling during different temperature ranges. [ABSTRACT FROM AUTHOR]

Abstract A series of Co 0.5-x Ni x Zn 0.5 Fe 2 O 4 (x = 0–0.25 insteps of 0.05) nano crystalline ferrites were synthesized in combustion method using citric acid as fuel. Densities and porosities were calculated using the lattice constant and Archimedes's principle. A linear increase in experimental density and a decrease in porosity were observed with increase in nickel concentration. Cationic distribution was proposed on the basis of theoretical lattice constant and it was correlated with the variation in magnetic and electrical properties of all samples. TEM image of the sample with nickel concentration x = 0.15 indicated the existence of nano-metric range particles and the sample was characterized with the help of inter-planar spacing(s) from SAED pattern. Morphological and surface analysis was studies using Scanning Electron Microscopy and well developed nearly spherical grains were observed with increase in nickel concentration. Energy Dispersive Spectroscopic (EDS) analysis was performed for all nickel substituted samples and all displayed stoichiometric proportions of ions in the samples as per the chemical composition. Elemental mapping was done for all samples using EDS data. Curie temperature was dropped nearly 90 °C at the end of the series. Initial permeability showed slight variation with an increase in nickel concentration and it remained nearly constant with frequency up to 3 MHz. Magnetic loss was observed to be constant for all samples after 100 kHz. DC Electrical resistivities of all samples were measured and all samples displayed resistivity in the order of 108 Ω-cm. AC resistivity and dielectric studies were conducted from 100 Hz to 5 MHz for all samples. Dielectric constant and losses of all samples exhibited very low values compared to that of conventional ferrites. The electrical properties of all samples were discussed with the help of temperature variation of resistivity, activation energy, grain size, density and porosity. [ABSTRACT FROM AUTHOR]

Abstract Nanosized powder of (Y 0.5 Bi 0.5) 3 (Fe 0.5 Ga 0.5) 5 O 12 ferrite garnet with a narrow particle size distribution was prepared via the gel auto-combustion approach based on polyvinyl alcohol (PVA) and metal nitrates. The peculiarities of garnet phase formation were studied by infrared spectroscopy (IR spectroscopy), simultaneous thermal analysis (TGA/DSC), C, H and N-elemental analysis, and powder X-ray diffraction (XRD). The final powdery product was characterized using powder XRD, IR spectroscopy, X-ray fluorescence (XRF) and scanning electron microscopy (SEM). We established that the use of PVA provides one-stage crystallization of a single-phase ferrite-garnet due to the formation of a thermally stable PVA-salt complex. Crystallization of the (Y 0.5 Bi 0.5) 3 (Fe 0.5 Ga 0.5) 5 O 12 powder occurred at 700 °C, without intermediate and impurity phases. [ABSTRACT FROM AUTHOR]

Abstract Microstructural changes including grain growth and densification in ferrite ceramic materials, either through liquid phase sintering or by lowering reaction energy, have a profound effect on the material properties. In this work, Li 0.365 Zn 0.27 Fe 2.365 O 4 (LZN) nanoparticles were prepared by sol-gel method. HRTEM image of the LZN nanoparticles showed that the spinel structure nanoparticles with ~26 nm average particle size were obtained at 500 °C. As a reaction additive, the LZN nanoparticles were introduced into a Bi-substituted Li 0.43 Zn 0.27 Ti 0.13 Fe 2.17 O 4 (LiZnTiBi) ferrite ceramic to control abnormal grain growth and enhance magnetic properties. XRD patterns demonstrated that a pure spinel phase structure composite ceramics were synthesized. This indicated the LZN nanoparticles can further react with LiZnTiBi ferrite ceramics. Also, SEM images showed that adding LZN nanoparticles can obviously control abnormal grain growth and reduce pores between grains. More importantly, results of ferromagnetic resonance (FMR) linewidth (Δ H) showed that optimized LZN nanoparticles additives can reduce ΔH of the LiZnTiBi ceramics (reduced to ~185.53 Oe). Meanwhile, saturation magnetization (4πM s) of the ceramics can be improved (up to 4504.96 gauss) by adding 2.00 wt% LZN nanoparticles. The doping method reported in this study also provides a referential experience for other low temperature sintering ceramics. [ABSTRACT FROM AUTHOR]

Abstract (BaFe 11.9 Al 0.1 O 19) 1- x - (BaTiO 3) x with x = 0, 0.25, 0.5, 0.75 and 1 bicomponent ceramics has been prepared from single-phase compounds of BaFe 11.9 Al 0.1 O 19 (x = 0) (BFO) and BaTiO 3 (x = 1) (BTO) by a standard ceramic technique. The constituent materials have been chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BFO and BTO. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and dielectrical properties versus chemical composition (x) have been performed. The ferrimagnetic phase transition temperature is almost independent of the BTO content, which is determined by intensity of the Fe3+-O2--Fe3+ indirect superexchange interactions in the BFO hexaferrite phase. However, the coercivity of composite samples is lower due to the contribution of the microstructure-dependent shape anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BTO at ~ 400 K and BFO at ~ 700 K. It has been observed that the dielectrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behavior has been discussed in terms of microstructure analysis and such parameters as the grain size, porosity and density. [ABSTRACT FROM AUTHOR]

Ferrimagnetic nanoparticles of SrFe 12−x (Mn 0.5 Sn 0.5 ) x O 19 was synthesis by controlling the effective processing parameters of sol-gel techniques. Microwave, magnetic properties and structure of nanosize, high purity sol-gel synthesized SrFe 12−x (Mn 0.5 Sn 0.5 ) x O 19 hexaferrite ferrimagnetic nanoparticles were investigated by vector network analysis, vibrating sample magnetometry, EDS and XRD. 57Fe Mössbauer spectroscopy was employed to find the occupancy sites of incorporated cations. The position of manganese and tin in 12k sites caused reduction in coercivity and magnetization saturation. The values of coercivity and magnetization saturation show that superparamagnetism did not occur in the synthesized products. Results demonstrate that additions of manganese and tin to hexagonal ferrite enhance bandwidth and reflection loss. Such composition could be proposed as a suitable electromagnetic wave absorber in microwave frequencies. [ABSTRACT FROM AUTHOR]

Isothermal crystallization kinetics was studied for Y 3 Al 5 O 12 obtained from amorphous dispersed phases based on aggregately stable sols of yttrium aluminum hydroxides. To describe the formation of yttrium aluminum garnet from the amorphous phases, a mathematical model involving intermediate Y 4 Al 2 O 9 and YAlO 3 phases has been proposed. From the obtained experimental data on the phase composition of the crystallizing system, kinetic parameters of the crystallization process were determined, which allowed us to propose a probable mechanism of YAG crystallization from hydrosols of various composition. The actual mechanism of garnet formation depends not just on the temperature treatment conditions of the amorphous phase, but also on the type of the precursors. The optimization of the time–temperature regimes of YAG crystallization allowed preparation of samples with required properties. Thus, the sol–gel method involving sols of high stability towards aggregation is shown to be promising for the production of high-quality powders and optical ceramics of yttrium aluminum garnet. [ABSTRACT FROM AUTHOR]

A series of substituted lithium ferrite samples Li 0.5− x Ni x Cu x Fe 2.5− x O 4 , with substituent concentration x =0–0.25 in steps of 0.05, were prepared by conventional double sintering ceramic method. The effect of nickel and copper co-substitutions on structural properties of the samples has been studied using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and vibration sample magnetometer techniques. The lattice parameter has been observed to increase with the increase in concentration ( x ) whereas the saturation magnetization was observed to increase from x ≥0.10 onwards. The observed variations are explained by suggesting transfer of a fraction of Cu ions from octahedral sites to tetrahedral sites at higher substituent concentrations. Theoretical lattice parameters and net magnetic moments per formula were calculated for all the samples by carefully assigning cation distributions so as to obtain a satisfactory agreement with experimental results of the same parameters. The observed infrared spectra of the samples with two distinct peaks for tetrahedral and octahedral metal–oxygen complexes further confirm the formation of spinel structures. Also, the observed variation of tetrahedral site radii which has been found in opposite to that of the tetrahedral absorption band further confirms that the proposed cation distributions are accurate for the investigated Li 0.5− x Ni x Cu x Fe 2.5− x O 4 system. [ABSTRACT FROM AUTHOR]