Inverse Spinel Phase Research Articles

Enhancement in Magnetic and Magnetocaloric Properties of CoFe2O4 Nanofibers at Lower Temperatures

AbstractThis research paper investigates new and first insights into the magnetic and magnetocaloric properties of one-dimensional (1D) cobalt ferrite CoFe2O4 (CFO) nanofibers (NFs) fabricated using a sol–gel-based electrospinning technique, focusing in particular on their behavior at low temperatures for specific applications. The microstructural, structural, magnetic, and magnetocaloric properties of the calcined CFO NFs were explored. The microstructure of the NFs, with an average diameter of 210 nm, was examined by scanning and transmission electron microscopy (SEM, TEM). The x-ray diffraction (XRD) of the CFO NFs showed a pure cubic close-packed (ccp) spinel crystalline structure with the Fd$$\overline{3}$$ 3 ¯ m space group. The Raman spectroscopic studies further confirm the cubic inverse spinel phase. The magnetic properties were explored as a function of temperature, ranging from 10 K to 300 K, and ferromagnetic behavior was observed with the highest saturation magnetization of 75.87 emu/g and coercivity of 723 Oe at room temperature. The variation of the magnetic entropy was measured indirectly using the Maxwell approach with an increasing magnetic field. A maximum of $$\left| {\Delta S} \right|$$ Δ S = 1.71 J/K was reached around 32 K. At 180 K, the associated adiabatic temperature change, ΔTmax, was 0.93 K, with a large RCP value of 7.58 J/kg, which is reasonably high for the corresponding nanoparticles (NPs). This work suggests that 1D CFO NFs offer a promising route for the production of nanostructured magnetic materials, potentially impacting various electronic and electromagnetic device applications at low temperatures.

Frequency-influenced dielectric analysis of sol-gel assisted Mg2+ substituted ZnMn2O4 nanoparticles

This study deals with the effect of Mg2+ doping on the structural, optical, and dielectric properties of zinc manganite nanoparticles. A series of MgxZn1-xMn2O4 (x = 0–0.5) samples were prepared with an auto-combustion synthesis method. Rietveld refinement of XRD revealed a pure tetragonal inverse spinel phase, supported by FTIR spectral analysis. Morphological studies indicated the transformation of micro-spherical to rod-like shapes for doped samples. With increased dopant concentration, the three Raman active modes shift towards higher frequencies. The co-existence of Mn2+, Mn3+, and Mn4+ states was revealed by chemical state analysis. The MZMO-5 sample exhibited the smallest energy bandgap (∼1.64 eV). The refractive indices of these samples were estimated to be ∼ 0.4 which might be useful for switching and filter circuits. These nano-manganite samples exhibited high dielectric constants and low losses, indicating their potential use in communication devices.

Strontium doping-tailored inverse spinel phase in cobalt chromite with enhanced photo-degradation of ofloxacin

Spinel materials are attractive to photocatalytic degradation of contaminants. In this study, strontium (Sr) doped spinel cobalt chromite (CoCr2O4) was synthesized by solution combustion method and characterized using techniques such as X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS). 30 -50 nm-cubic CoCr2O4 nanocrystals were obtained, and phase transitions of CoO6→CoO4 and CrO4→CrO6 occurred as the Sr doping content increased until 0.6 % Sr doped sample displayed an inverse spinel phase. The modifications in composition and structure induced the co-existence of multivalent states for Co and Cr, which in turn changed the optical, complex impedance, and magnetic spin state of CoCr2O4. The 0.6 % Sr-doped sample showed the highest photocatalytic efficiency of 93 % due to enhanced optical absorption, reduced energy band gap, oxygen vacancies formation, and a high spin state of Co. The XRD structure and photocatalytic activity remained stable even after five cycles without any leakage of metal elements. The degradation pathway and Mott-Schottky curves were employed to elucidate the mechanism behind this enhancement. The strategy employed in this study proved effective, and the synthesized materials show promise for the photocatalytic degradation of contaminants.

Synthesis and characterization of Fe3O4 core nanoparticles coated with TiO2 and ZnO

The room temperature synthesis of the core-shell-shell (CSS) nanoparticles was demonstrated to be green, low-cost, and reproducible. The magnetic core of Fe3O4 nanoparticles was coated with TiO2 and ZnO in two steps. The obtained CSS nanoparticles were extensively characterized by XPS, TEM, XRD, DRS-UV–vis, N2 Physisorption, Electromagnetic, and Raman spectroscopy. XPS analysis revealed that the magnetic core was successfully functionalized with the citric acid. The ratio between the ferric cations (Fe3+) and ferrous (Fe2+) is typically reported to be around two due to the presence of FeO and Fe2O3 to balance the charge in the structure. Nevertheless, XPS results demonstrated that the ratio resulted in higher stability than that of the crystal nominal structure, suggesting that the surface of the CSS is slightly enriched with Fe3+ cations. TEM results indicated an average core diameter of approximately 9±1 nm for Fe3O4 (M-US); the first shell exhibited an average thickness of 3±1 nm, while the ZnO second shell thickness resulted in around 2±1 nm. X-ray diffraction analysis identified inverse spinel, hematite, anatase, and zincite phases in M-US, MT, and MTZ, respectively. Notably, the MTZ sample also contained hematite in addition to inverse spinel. Diffuse Reflectance UV-Vis Spectroscopy results demonstrated a reduction in the band gap as the shell coverage varied. N2 adsorption-desorption isotherms indicated an increase in the surface area as the core nanoparticles were coated with the subsequent shells. Additionally, the coated samples presented a mesoporous structure with a maximum surface area of 110 m2g−1 for the MT material. Raman spectroscopy confirmed the presence of vibrational modes related to TiO2 and ZnO. The core-shell-shell nanoparticles presented suitable electronic properties to potentially be applied in the photodegradation of harmful compounds and azo dyes.

Revealing the role of crystal structure to catalysis: Inverse spinel phase Co-Mn-based catalyst for Li-S batteries

Li-S batteries are a promising energy storage system because of their inexpensive price and high theoretical energy density (2600 Wh kg−1). However, the actual performance of Li-S batteries is still hampered by the severe shuttle effect and the slow reaction kinetics of lithium polysulfides (LiPSs). Balancing the high energy density and long cycle life of Li-S batteries still face many challenges. In this work, inverse spinel phase Co-Mn bi-metal oxides are proposed as an advanced sulfur reduction reaction (SRR) catalyst to prevent irreversible loss of sulfur species and accelerate the reaction kinetics of Li-S batteries. It has been found that both normal spinel phase Co2MnO4 (n-CMO) and inverse spinel phase CoMn2O4 (i-CMO) have significant catalytic activity to the conversion reaction of sulfur species. In the same time, based on the electrochemical impedance spectroscopy (EIS) in variable temperature and in situ ultraviolet visible (Uv–vis) spectroscopy, it has also been found that the i-CMO catalyst shows much better performance than n-CMO since it could reduce the activation energy of SRR reaction and promote the dissociation of the S8 ring. As a result, the i-CMO/S cathode delivers a high initial discharge specific capacity of 1386 mAh/g at 0.1C together with a low-capacity fading rate of 0.11 % per cycle within 400 cycles. Besides, when the i-CMO nanoparticles are loaded on the surface of carbon cloth (CC), the CC@i-CMO/S cathode provides a high areal capacity of 4.26 mAh cm−2 at 0.1C, in which sulfur areal loading is 3.54 mg cm−2. Therefore, this study is a positive attempt to study the relationship between catalytic performance and the crystal structure of the materials, which will be conducive to the practical use of Li-S batteries.

Efficient direct repairing of lithium- and manganese-rich cathodes by concentrated solar radiation

Lithium- and manganese-rich layered oxide cathode materials have attracted extensive interest because of their high energy density. However, the rapid capacity fading and serve voltage decay over cycling make the waste management and recycling of key components indispensable. Herein, we report a facile concentrated solar radiation strategy for the direct recycling of Lithium- and manganese-rich cathodes, which enables the recovery of capacity and effectively improves its electrochemical stability. The phase change from layered to spinel on the particle surface and metastable state structure of cycled material provides the precondition for photocatalytic reaction and thermal reconstruction during concentrated solar radiation processing. The inducement of partial inverse spinel phase is identified after concentrated solar radiation treatment, which strongly enhances the redox activity of transition metal cations and oxygen anion, and reversibility of lattice structure. This study sheds new light on the reparation of spent cathode materials and designing high-performance compositions to mitigate structural degradation.

Sol-gel combustion synthesis of porous Mg2SnO4@SnO2 nanocomposites: A study on the structural parameters, optical properties, and electrochemical activity

In this work, a magnesium stannate-tin oxide nanocomposite (Mg2SnO4@SnO2) was prepared using the sol-gel combustion method. The physical properties of the products have been characterized by different analysis techniques. The XRD results revealed the combined structure of the cubic inverse spinel phase of Mg2SnO4 and the tetragonal phase of SnO2 with a mean crystalline size of 5.1 nm. The average grain sizes of SnO2 and Mg2SnO4@SnO2 from FESEM images were about 51.98 nm and 58.18 nm, and TEM images revealed that the size of nanoparticles were about 30–200 nm and 20−50 nm, respectively. The band gap energy of Mg2SnO4@SnO2 NPs was estimated to be about 3.9 eV. Results from FESEM and BET revealed the sample's sponge-like meso/macroporous morphology. PL spectra have revealed a blue emission. The optical constants of Mg2SnO4@SnO2 deposited on the glass substrate were determined using UV–Vis transmittance data and theoretical approaches. The electrochemical performances of the porous Mg2SnO4@SnO2 deposited on ITO-coated glass substrate and metal foam (Ni and Cu) substrates as particulate composites by doctor blade technique were compared by GCD, CV, and EIS analysis. The best performance is belonged to the Mg2SnO4@SnO2/Cu foam electrode with a specific capacitance of 675 Fg-1 at a current density of 1 Ag-1. Mg2SnO4@SnO2/Ni foam has a higher capacitance retention rate, which showed stability of 86.27 % over 5000 charge/discharge cycles at a current density of 10 Ag-1.

Effect of synthesis routes on electrochemical properties as supercapacitor electrode for novel spinel (CuNiFeMnCo)3O4 high entropy oxide

AbstractThe aim of the present study is to investigate the effect of synthesis routes on phase evolution, microstructure, change in ionic state and their co‐relation with electrochemical charge storage, and magnetic properties of novel (CuNiFeMnCo)3O4 high entropy spinel oxide (HESO). We successfully synthesized novel (CuNiFeMnCo)3O4 HESO through two different synthesis methods, that is, sol‐gel and reverse coprecipitation methods abbreviated as SA‐1 and SA‐2, respectively. The XRD analysis for both samples reveals the formation of inverse spinel phase (space group Fd‐3m) with the lattice constant of 8.3602 and 8.2502 Å for SA‐1 and SA‐2, respectively. The sample synthesized through the sol‐gel method possessed porous morphology, whereas the sample synthesized through the reverse coprecipitation method had spherical particles. The x‐ray photoelectron spectroscopy confirmed the presence of +2 and +3 ionic states for Fe, Ni, and Co, while Cu has a + 2 state and Mn exist in +3 and +4 states for both the synthesized samples. The ionic states of all cations remain invariant irrespective of the synthesis methods. However, the concentration of oxygen vacancy is significantly different for samples synthesized through different routes. Both the HESO electrodes show the electrochemical double‐layer capacitive type behavior in 2 M KOH electrolytic solution. The value of maximum specific capacitance is 38.46 and 34.24 F/g at a scan rate of 5 mV/s for SA‐1 and SA‐2, respectively. Moreover, the electrodes have capacity retention of 90 and 99% for 1000 cycles at a scan rate of 50 mV/s for SA‐1 and SA‐2, respectively. The magnetic property of the synthesized HESO samples was also investigated, and the found values of magnetization and coercivity are 1.79 emu/g and 54.9 Oe and 8.5 emu/g and 67.69 Oe for SA‐1 and SA‐2, respectively.

Electrochemical charge storage properties of novel inverse spinel (CuNiZnAlFe)3O4 type high entropy oxide

AbstractThe novel (CuNiZnAlFe)3O4 type nanocrystalline High Entropy Oxide (HEO) was synthesized through the sol‐gel method with combustion at 350°C for 1 h duration. The XRD analysis reveals the formation of inverse spinel [B(AB)O4] type phase indexed with the space group of Fd‐3 m confirmed through the Rietveld Refinement of the XRD data. The lattice constant for the synthesized spinel phase was found to be 8.2453°A. The Scanning Electron Microscope of the synthesized HEO confirms the flakes‐like morphology with porous microstructure. The Energy Dispersive X‐ray (EDX) analysis and elemental mapping confirm the homogeneous distribution of the cations over the selected region. It was found that Fe and Ni are in the +3 and +2 states, other cations, Cu and Zn, are in the +2 states, and Al is in the +3 confirmed through the X‐ray photoelectron Spectroscopy. The electrochemical performance was studied in three electrodes in a 2 M KOH aqueous electrolyte. The specific capacitance value was 2.02, 1.58, 1.24, 1.06, 0.87, 0.71, and 0.65 F/g at scan rates of 5, 10, 20, 30, 50, 80, and 100 mV/s, respectively. The low value of specific capacitance was observed due to the stable ionic structure of the inverse spinel phase. The magnetization behavior of the sample is also investigated. The M‐H loop of the (CuNiZnAlFe)3O4 HEO sample exhibits a ferrimagnetic nature.

Influence of (Zn0.5Ti0.5)3+ substitution on structural evolution, bond characteristics, and microwave dielectric properties of spinel Li(Zn0.5Ti0.5)xGa5-xO8 solid solutions

In this study, the evolution of phase and bond characteristics, as well as the consequent effects on the microwave dielectric properties of Li(Zn0.5Ti0.5)xGa5-xO8 ceramics were investigated. XRD and Rietveld refinement patterns revealed that the sample underwent a transformation from a low-symmetry inverse cubic spinel phase, characterized by the P4332 space group, to a high-symmetry cubic spinel phase associated with the Fd-3m space group. All samples displayed compact grain structures in their surface micro-morphologies, and they achieved high relative densities exceeding 97% when sintered at their respective optimal temperatures. With increasing x value, the dielectric constant increases due to the growth in ionicity and αtheo/Vm. Concurrently, the τf value shifts from −69.29 ppm/°C to −48.73 ppm/°C, a trend that aligns with the bond valence changes at the octahedral position as a function of x. In the range of 0 ≤ x ≤ 3, the Q × f value initially increased due to the change in symmetry, growth in lattice energy, and reduction of Ti3+ content. However, it subsequently decreased as a result of further disruption in ordering and diminishing lattice energy. The optimal microwave dielectric properties were obtained for the x = 3 sample (LiZn1.5Ti1.5Ga2O8) sintered at 1220 °C, displaying characteristics of εr = 16.46, Q × f = 79,268 GHz and τf = −53.36 ppm/°C.

Investigation of the adsorption of the tetracycline antibiotic by NiFe2O4 and CoFe2O4 nanoparticles

Tetracycline is a bacteriostatic antibiotic with stable chemical composition, which difficults its degradation in the environment. The presence of this antibiotic in the aquatic environment can cause toxic effects and potential development of resistant bacteria. In this work, the structural and magnetic properties of NiFe2O4 and CoFe2O4 nanoparticles and their applications in tetracycline adsorption were investigated. Ferrites were synthesized by coprecipitation, heat treated at 623 K for 2 h and characterized by thermogravimetric analysis, X-ray diffractometry, Fourier transform infrared spectroscopy, Mössbauer spectroscopy, vibrating sample magnetometry, electrophoretic light scattering and gas adsorption. The experimental data confirmed the formation of the partially inverse spinel phase of NiFe2O4 and CoFe2O4, with crystallite sizes of 6 and 4 nm, respectively, superparamagnetic behavior, low saturation magnetization and coercivity, isoelectric point close to pH 7 and mesoporous structure. NiFe2O4 exhibited better performance in the adsorption of tetracycline (50 mgTCN.g-1NiFe2O4 and 96% removal) at pH 7. FTIR and XPS spectroscopy measurements indicate that the main adsorption mechanism is hydrogen bonding.

Mesoporous Zn2SnO4 for efficient sensing of ethylene glycol vapor

Within this study, mesoporous Zn2SnO4 nanostructures have been prepared by a facile and eco-friendly hydrothermal method. Through X-ray diffraction analysis, a polycrystalline zinc tin oxide structure is recognized with a cubic inverse spinel phase crystal structure. By Field emission scanning electron microscopy method, various morphologies based on the hydrothermal time ranging from the cubic-like morphology, irregular hexagonal plates, and large quantity of microspheres to the truncated octahedron have been observed. By the aid of Energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy analyses, the atomic ratio and characteristic vibration peaks of Zn2SnO4 have been evaluated. By the help of Brunauer–Emmett–Teller analysis, specific surface area, mean pore diameter, and total pore volume were measured. The nanostructured Zn2SnO4 prepared in 36 h hydrothermal treatment (as a selected sample) showed a higher BET specific surface area (9.10 m2/g) and total pore volume (0.078 cm3/g) than the other samples. The gas-sensing performance of the samples was investigated towards different vapors. The optimum operating temperature (270 °C), transient response, response/recovery times, and long-term stability (eight months) of the samples have been evaluated. For the selected sample, appreciable sensing response (92.92 toward 100 ppm ethylene glycol), the ultra-fast response time (1 s), excellent selectivity (about 6–23 times more than other tested vapors) and excellent long-term stability (the response decay of about 10% after eight months) has been perceived which makes it a promising gas sensor. It seems that the selected sample has shown relatively better performance for two reasons: Firstly, high crystalline quality (largest crystallite size and lowest strain value) which can affect the combination or separation of adsorbed oxygen species on the surface of the material. Secondly, the higher specific surface area and the relatively larger total pore volume can lead to more gas adsorption sites leading to further narrowing of the depletion layer and resulting in a high and very fast response.

Compressibilities along the magnetite–magnesioferrite solid solution

To calculate the thermodynamic properties of recently discovered high-pressure mixed valence iron oxides in the system Fe–Mg–O, information on the equation of state of precursor inverse spinel phases along the magnetite–magnesioferrite join is needed. The existing equation of state data, particularly for magnesioferrite, are in poor agreement and no data exist for intermediate compositions. In this study, the compressibility of nearly pure magnesioferrite as well as of an intermediate {{mathrm{Mg}}_{0.5}}^{vphantom{2+}}mathrm{Fe}_{0.5}^{2+}{mathrm{Fe}}_{2}^{3+}{mathrm{O}}_{4}^{vphantom{2+}} sample have been investigated for the first time up to approximately 19 and 13 GPa, respectively, using single-crystal X-ray diffraction in a diamond anvil cell. Samples were produced in high-pressure synthesis experiments to promote a high level of cation ordering, with the obtained inversion parameters larger than 0.83. The room pressure unit cell volumes, V0, and bulk moduli, KT0, could be adequately constrained using a second-order Birch–Murnaghan equation of state, which yields V0 = 588.97 (8) Å3 and KT0 = 178.4 (5) GPa for magnesioferrite and V0 = 590.21 (5) Å3 and KT0 = 188.0 (6) GPa for the intermediate composition. As magnetite has KT0 = 180 (1) GPa (Gatta et al. in Phys Chem Min 34:627–635, 2007. https://doi.org/10.1007/s00269-007-0177-3), this means the variation in KT0 across the magnetite–magnesioferrite solid solution is significantly non-linear, in contrast to several other Fe–Mg spinels. The larger incompressibility of the intermediate composition compared to the two end-members may be a peculiarity of the magnetite–magnesioferrite solid solution caused by an interruption of Fe2+–Fe3+ electron hopping by Mg cations substituting in the octahedral site.

Antibacterial activity of PANI coated CoFe2O4 nanocomposite for gram-positive and gram-negative bacterial strains

We report on the synthesis of Polyaniline (PANI) coated cobalt ferrite (CoFe2O4) [CoFe2O4/PANI] nanocomposite and study their antibacterial activity for gram-positive (S. aureus, B. subtillis) and gram-negative (E. coli, P. aeruginosa) bacterial strains. PANI coated CoFe2O4 nanocomposites have been synthesized by in-situ chemical oxidative polymerization of aniline monomer on CoFe2O4 nanoparticles, which were synthesized by chemical co-precipitation followed by hydrothermal method. The X-ray diffraction of as-synthesized CoFe2O4 nanoparticles and CoFe2O4/PANI nanocomposite revealed the polycrystalline inverse spinel phase and semi-crystalline nature of PANI. Transmission electron microscope images affirm the incorporation of CoFe2O4 nanoparticles of 5 nm average particle size into the PANI matrix. The saturation magnetization of CoFe2O4/PANI nanocomposites was recorded 50% (54 emu/g to 27 emu/g) in comparison to CoFe2O4 nanoparticles. The antibacterial activity of PANI coated CoFe2O4 nanocomposites were studied by Agar well diffusion method. The results showed a clear inhibition zone, as an antibacterial agent, CoFe2O4/PANI nanocomposites exhibited good antibacterial activity against a different bacterial cell's growth. Growth kinetics studies show that percentage inhibition is relatively higher for P. aeruginosa (~ 92%) than other studied bacteria at 5 mg/ml of the nanocomposites.

Link between Structural and Optical Properties of CoxFe3–xO4 Nanoparticles and Thin Films with Different Co/Fe Ratios

CoxFe3–xO4 nanoparticles (x = 0.4 to x = 2.5) and thin films (x = 0.9 to x = 2.2) are analyzed by Raman, absorption, and photoluminescence spectroscopy to link structural and optical properties to different cobalt to iron (Co/Fe) ratios. Raman spectroscopy shows that with decreasing Co content, the crystal structure changes from a predominantly normal cubic spinel phase to a mixed inverse spinel phase. This finding is supported by absorption spectroscopy that points out that inter valence charge transfer (IVCT) processes between octahedrally coordinated Co2+ and Fe3+ cations become more prominent with increasing Fe content. Independent of the Co/Fe ratio, CoxFe3–xO4 nanoparticles show a broad photoluminescence (PL) band with a maximum at around 510 nm. Time-resolved photoluminescence spectroscopy shows subnanosecond lifetimes and temperature-resolved photoluminescence experiments reveal that the green PL increases with decreasing temperature (300 to 10 K) while showing no temperature-dependent shift in energy. It is proposed that this green PL originates from OH-groups on the particles’ surface.

Structural, magnetic, and impedance properties of Co1-xZrxFe2O4 nanocrystallites by PEG-assisted sol-gel route

This work presents the Zr4+-substituted CoFe2O4 nanocrystallites at lower concentrations prepared via sol-gel method in order to investigate their structural and magnetic properties along with their impedance properties. XRD patterns confirm the inverse spinel phase of CoFe2O4 and the presence of zirconium (Zr) nanoparticles in the spinel network. The crystallite size was found to decrease after Zr substitution. CoFe2O4 nanocrystallites of 34-nm size and lattice parameter slightly increase with Zr4+ substitution into cobalt ferrite as observed from the XRD pattern. The presence of all functional groups involved in the present synthesis was determined from FTIR spectroscopy. Characteristic peaks of cubic spinel structured cobalt ferrites are observed in the Raman spectrum of each ferrite composition. The HRSEM images revealed the spherical morphology and nanosize of the Zr4+-doped CoFe2O4 nanocrystallites. EDX analysis confirmed that the applied process for the fabrication of Co1-xZrxFe2O4 nanoparticles is a proper process for the synthesis of spinel cobalt ferrites with homogeneity in composition. The TEM images evidently exposed formation of well-shaped nanoparticles and the fringes are uniform with 0.44-nm width and the selected area electron diffraction pattern exposed periodic arrangements. The results of magnetic hysteresis revealed that the zirconium-substituted cobalt ferrite nanoparticles increase the saturation magnetization and coercivity with increasing zirconium content. Impedance increased when Zr4+ was substituted, but for higher concentration it was reduced.

Eco-Friendly Synthesis, Crystal Chemistry, and Magnetic Properties of Manganese-Substituted CoFe2O4 Nanoparticles.

The authors report on the effect of manganese (Mn) substitution on the crystal chemistry, morphology, particle size distribution characteristics, chemical bonding, structure, and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles (NPs) synthesized by a simple, cost-effective, and eco-friendly one-pot aqueous hydrothermal method. Crystal structure analyses indicate that the Mn(II)-substituted cobalt ferrites, Co1–xMnxFe2O4 (CMFO, x = 0.0–0.5), were crystalline with a cubic inverse spinel structure (space group Fd3m). The average crystallite size increases from 8 to 14 nm with increasing Mn(II) content; the crystal growth follows an exponential growth function while the lattice parameters follow Vegard’s law. Chemical bonding analyses made using Raman spectroscopic studies further confirm the cubic inverse spinel phase. The relative changes in specific vibrational modes related to octahedral sites as a function of Mn content suggest a gradual change of measure of inversion of the ferrite lattice at nanoscale dimensions. Small-angle X-ray scattering and electron microscopy revealed a narrow particle size distribution with the spherical shape morphology of the CMFO NPs. The zero-field-cooled and field-cooled magnetic measurements revealed the superparamagnetic behavior of CMFO NPs at room temperature. The sample with x = 0.3 indicates a lower value of blocking temperature (9.16 K) with the improved (maximum) value of saturation magnetization. The results and the structure-composition–property correlation suggest that the economic, eco-friendly hydrothermal approach can be adopted to process superparamagnetic nanostructured magnetic materials at a relatively lower temperature for practical electronic and electromagnetic device applications.

Nickel ferrite embedded polyvinylidene fluoride composite based flexible magneto-electric systems

Developing flexible multiferroic composite with magnetoelectric coupling is highly desirable for the wearable electronic devices, magnetic field sensors, actuators, energy harvesters and memory devices. Here, a flexible artificial multiferroic composite was fabricated using ferromagnetic nickel ferrite (NiFe2O4) nanoparticles (NPs) as filler in the ferroelectric polyvinylidene fluoride (PVDF) matrix. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed the formation of the inverse spinel phase in NiFe2O4 NPs. The vibrating sample magnetometer (VSM) and XRD measurements showed an increase in the magnetic moment and the electroactive β phase fraction, respectively, in PVDF/NiFe2O4 composite with the increasing loading concentration of NiFe2O4 filler NPs. With the increase in NiFe2O4 NPs loading concentration to 40 wt % the magnetoelectric coupling between the ferroelectric (PVDF) and ferromagnetic (NiFe2O4 NPs) was confirmed using magnetocapacitance measurement. This work successfully demonstrates the potential of artificial multiferroic PVDF/NiFe2O4 composite system, with enhanced dielectric property and room temperature magnetoelectric coupling, for future flexible electronic devices.

Electronic structure, magnetic and optic properties of spinel compound NiFe2O4

We report ab initio investigation of structural, electronic, magnetic and optical properties of the NiFe2O4 compound. Hubbard parameters are computed for both Ni and Fe atoms. Employing generalized gradient approximation (GGA) and GGA + U approximations and taking into consideration four possible types of atomic arrangements, we identify the most stable structural–magnetic configuration of the system. Interestingly, the inverse spinel NiFe2O4 compound is found to exhibit a ferrimagnetic structure. The ground state structural lattice parameters and the interatomic distances of spinel NiFe2O4 compound are computed. Furthermore, band structure calculations demonstrate that NiFe2O4 compound exhibits large band gaps in both spin configurations with a large magnetic moment. Energetically, ferrite nickel favors the inverse spinel phase in which Fe and Ni cations in either octahedral or tetrahedral sites adopt the high-spin configuration. We found that the energy of the normal spinel is higher than that of the inverse spinel, confirming that inverse spinel is the most stable structure of the NiFe2O4 compound. The optical behavior of the NiFe2O4 compound is characterized by calculating the real and imaginary part of the dielectric function, the absorption coefficients, the refractive index, the optical conductivity and the energy loss. Optimizing structural, electronic, magnetic and optical properties of this novel compound is crucial for exploring and utilizing it for modern device applications.

Fabrication and characterization of ultraviolet detector based on epitaxial Ta-doped Zn2SnO4 films

Abstract Zn2SnO4 films with Ta concentrations from 0 to 5% were deposited on MgO(100) substrates via pulsed laser deposition, and annealed in air atmosphere at 800 °C. The structure, surface morphology, optical and electrical properties of the films were systematically studied. The obtained films were inverse-spinel phase Zn2SnO4 grown along [100] orientation and the crystal quality decreased with Ta content. All the Ta-doped Zn2SnO4 films exhibited high average transmittances of about 95% in visible region with optical band gaps ranging from 3.98 to 4.10 eV. The metal-semiconductor-metal ultraviolet (UV) detector fabricated using the 3% Ta-doped Zn2SnO4 film exhibited the best detection performance with high photoresponsivity in wavelength range of 200–280 nm. The photoresponsivity at 254 nm was 23.3 A/W and the photo-dark current ratio exceeded 104 at 5 V bias. The Zn2SnO4-based detectors also showed good repeatability of UV detection.