Octahedral Sites Research Articles

Investigation of negative permittivity in BaTiO3/TiN metacomposites at the radio frequency region

The intriguing and unexpected properties of metacomposites have attracted significant attention, especially in terms of tuning their negative permittivity. In this study, we fabricated percolative BaTiO3/TiN (BTN) metacomposites employing mesoporous BaTiO3 nanoparticles synthesized via a novel solvothermal method as the matrix, combined with varying concentrations of TiN as the filler. Dielectric properties investigated in the frequency range of 100 Hz to 100 kHz unveiled a transition in the permittivity, shifting from positive to negative as the TiN content increased (primarily noticeable at frequencies above 10 kHz). The initial permittivity shifting is associated with an enhanced interfacial polarization, commonly recognized as Maxwell-Wagner-Sillars effect observed below the percolation threshold. Further, Lorentz model is attributed to induce dielectric resonance in the BaTiO3 matrix triggered by the Ti4+ ions in Ti–O octahedral sites leading to negative permittivity in conjunction with increase in TiN particles above the percolation threshold. Interestingly, AC conductivity exhibited an increase with increasing frequency when TiN content was lower. However, intriguingly, this frequency-dependence in the conductivity of BTN metacomposites did not hold as TiN content increased. Moreover, the investigation of reactance revealed the inductive character derived from the conductive network, a conclusion further confirmed through equivalent circuit analysis. The findings presented in this study are poised to unlock new possibilities in the design and development of metacomposites, ultimately facilitating practical applications of epsilon-negative materials in electromagnetic devices.

Photoelectron Holographic Study for Atomic Site Occupancy for Si Dopants in Si-Doped κ-Ga2O3(001).

We investigated atomic site occupancy for the Si dopant in Si-doped κ-Ga2O3(001) using photoelectron spectroscopy (PES) and photoelectron holography (PEH). From PES and PEH, we found that the Si dopant had one chemical state, and three types of inequivalent Si substitutional sites (SiGa) were formed. The ratios for the inequivalent tetrahedral, pentahedral, and octahedral SiGa sites were estimated to be 55.0%, 28.1%, and 16.9%, respectively. Higher (lower) ratios for the three inequivalent SiGa sites may come from a lower (higher) formation energy. The Tetra (Octa) SiGa site has the highest (lowest) ratio of the three SiGa sites since it has the lowest (highest) formation energy. We suggest that the tetrahedral SiGa site is due to the active dopant site, whereas the pentahedral and octahedral SiGa sites can be attributed to the inactive dopant sites for Si-doped κ-Ga2O3(001).

First principles calculation of elastic properties of Fe–C alloys: Effect of interstitial and substitutional carbon element

The effect of different incorporation mechanisms on the elastic properties of hcp Fe–C alloys at high pressures is investigated using density functional theory combined with Monte Carlo special quasi-random structure method. It is found that the different incorporation mechanism has little effect on the bulk modulus B and the compressional wave velocity Vp of hcp Fe–C alloys. However, the values of the shear modulus G and the shear wave velocity Vs in substitutional doping form are generally larger than those in interstitial doping form, which are 17% and 8% higher than G and Vs in interstitial doping form at 250 GPa and 2.5 wt% carbon content. Interestingly, the elastic properties of Fe–C alloy are almost unaffected by interstitial doping sites (octahedral central site and tetrahedral central site) below 250 GPa.

Physical characterization, magnetic interactions and DC electrical resistivity properties of La3+ substituted NiZnCd nano ferrites

In this article, we substituted La3+ ions to explore the structural, magnetic, and DC electrical resistivity properties of Ni0.5Zn0.4Cd0.1Fe2-xLaxO4 (x = 0.0, 0.02, 0.04, 0.06, and 0.08) nano-structured spinel ferrites. We employed X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM) with Energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), Vibrating sample magnetometry (VSM), and electrical measurements to characterize the studied samples, which were synthesized using the sol–gel auto-combustion process. XRD analysis confirmed that the prepared materials formed a single-phase nanostructure. Using Debye-Scherer's formula, we calculated the average crystallite size, which ranged from 29.01 to 21.52 nm. FESEM images demonstrated that each sample exhibited spherical nanocrystalline behavior. The variations of the prepared samples were confirmed constitutionally by EDX. The FTIR data revealed two absorption bands for all synthesized materials at υ1 = 562.18 to 590.51 cm−1 and υ2 = 410.18 to 430.51 cm−1, corresponding to the tetrahedral and octahedral sites of the spinel structure, respectively. Vibrant sample magnetometry spectra were utilized to investigate how La3+-doping affects the magnetic characteristics of NiZnCd ferrite. Due to enhanced La3+-doping, saturation magnetization, and coercivity values decreased. The La3+ doping of NiZnCd nano ferrites resulted in changes in saturation magnetization (from 83.66 to 69.57 emu/g), coercivity (from 33.75 to 60.51 Oe), and remanence magnetization (from 29.62 to 33.12 emu/g). These variations suggest the potential utility of the samples for magnetic recording and memory applications. The semiconducting behavior has been confirmed by the DC electrical resistivity measured values using a two-probe method. Data on DC electrical resistivity were also utilized to determine carrier concentration and activation energy, establishing a connection with La3+ replacement.

Facile one-step preparation of Co2CrO4 spinel from heterometallic compounds – Structural, magnetic, electrical and photocatalytic studies

Two isostructural heterometallic complex salts with mononuclear units, [NH(CH3)2(C2H5)][Cr(terpy)2][CoCl4]2 (1) and [NH(CH3)(C2H5)2][Cr(terpy)2][CoCl4]2 (2), were synthesized using a building block approach and characterized by single-crystal and powder X-ray diffraction (XRD), impedance spectroscopy and magnetization measurements. They exhibit particular humidity-sensing properties and very high proton conductivity at room temperature. The magnetization of complexes shows the high spin state of 3/2 for tetrahedrally coordinated CoII ions, which on cooling remain in the paramagnetic state within the CrIII network, which is antiferromagnetically correlated. The prepared compounds were thoroughly explored as single-source precursors for the formation of the spinel oxide Co2CrO4 by their thermal decomposition. By optimizing the annealing temperature, heating/cooling rates and holding times, the phase composition of thermal processing of 1 or 2 was evaluated: phase pure spinel Co2CrO4 was obtained by thermal treatment already at 450 °C. The structure, morphology, and optical properties of spinel oxides prepared at different temperatures were characterized using powder XRD, field emission scanning electron microscopy (SEM) and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), while electrical and magnetic by impedance spectroscopy and magnetization measurements. The determined band gap energy and nanosized crystallites prompted us to investigate the photocatalytic activity of spinel oxide produced at 450 °C in the degradation of dyes Rhodamine B (RhB) and Methylene blue (MB) under Vis irradiation without and with assistance of hydrogen peroxide (H2O2). The results show that the Co2CrO4/H2O2 system exhibits a significantly higher photoactivity response; the degradation efficiency of MB and RhB was found to be 86.1% and 80.3%, respectively. The electrical conductivity spectra and the activation energy for the DC conductivity demonstrate the electronically semiconducting behaviour of the Co2CrO4 oxide. The Co2CrO4 spinel has a ferrimagnetic ground state, with mixed CoII and CoIII ions on the tetrahedral and octahedral sites: CoII having a high spin state on both sites and CoIII having a high spin state on the tetrahedral site and a low spin state on the octahedral site. Different thermal treatments affect the magnetization according to the different sizes of the obtained crystallites.

Adjusting the gas detection characteristics of NiFe2O4 spinel ferrite nanoparticles through the introduction of Zn doping

Nickel ferrite nanoparticles doped with zinc were synthesized at a lower reaction temperature of 180 °C. The research delved into their structural, optical, dielectric, and magnetic properties. These nanoparticles exhibited a distinct cubic spinel structure, with crystallite sizes ranging from 33 to 51 nm. FTIR analysis revealed metal oxide stretching vibrations between 400–600 nm. FESEM and HR-TEM examinations unveiled irregularly shaped nano-particles. XPS analysis disclosed the chemical states of Zn2+, Fe3+, and Ni2+ ions. Mossbauer spectra exhibited two sextet patterns related to tetrahedral (A) and octahedral (B) sites, plus a weak doublet pattern. Magnetic tests showed a decrease in saturation magnetization (Ms) but an increase in remanent magnetization (Mr) and coercivity (Hc) values upon doping.

Structural, magnetic and dielectric properties of cerium-doped manganese – cobalt ferrite nanoparticles

Co0.50Mn0.50Ce xFe2− xO4 (with x = 0.000, 0.025, 0.050 and 0.100) nanoparticles were synthesised through sol–gel method. The crystallite size and lattice constant are increased from 30 to 50 nm and 8.375 to 8.384 Å, respectively, with increasing Ce content. It was found that Fe3+ cations migrate towards octahedral sites with Ce doping. The optical band gap was decreased from 1.79 to 1.50 eV whereas saturation magnetisation was decreased from 57 to 49 emu/g with increase in Ce substitution. Maximum dielectric constant and minimum dielectric loss, maximum AC conductivity along with moderate magnetic properties were observed for x = 0.050. So, x = 0.050 may be a potential candidate for electromagnetic interference shielding applications.

Stabilization of unique Zr>4+ species in NiFe2O4 nanocrystals for unprecedented catalytic transfer hydrogenation reaction

Stabilization of transition metal species (like Zr>4+) with increasingly positive charge density at oxide surfaces is highly important for intrinsically improving catalytic performance for many uses like catalytic transfer hydrogenation (CTH) reaction, which however remains inaccessible. Here, we showcase a water-quenching strategy that stably achieves Zr>4+ species at surfaces of prototype spinel oxide NiFe2O4. Systematic investigation unveils that these Zr>4+species were precisely incorporated into surface octahedral Ni sites of NiFe2O4. The local electronic structure was thus regulated. As a consequence, there simultaneously appear electron depletion (Zr>4+) and accumulation (O2-) at the resulted sites, which play the distinct roles as Lewis acid-base sites in (i) facilitating O-H bond dissociation and CO bond activation, (ii) enhancing the interaction and bonding with substrate molecules, and (iii) reducing the energy barrier for hydrogen transfer process. The resulting catalysts exhibit superior catalytic performance and stability in the CTH reaction of biomass-derived carbonyls and representative aldehydes/ketones, especially the reduction of furfural to furfuryl alcohol with a yield of 90.7% under 120 ℃ for 3 h. This work provides new insights into optimizing catalytic activity in metal oxides by stabilizing transition metal species with unexpectedly positive charge density.

Mössbauer, optical and structural properties of [formula omitted] ion in borate glass

Lanthanum-bearing iron lithium borate glass is a quaternary system for oxide glasses and was prepared via the melt-quenching method. The present article correlates the structure, optical, ligand field and Mössbauer data on iron lithium borate glass containing La3+. The density was measured, while the molar volume was calculated. Other physical parameters are well-described. With increasing the La2O3 content within the glass network, infrared spectra analysis reveals structural modifications such as the increase in BO4 units and the decline in both BO3 units and NBO bonds content. Furthermore, optical absorption spectra were measured. The absorption spectra disclose a plethora of electronic transitions that are related to Fe3+ in tetrahedral and octahedral sites, however, Fe2+ phase is not observed in optical spectra, but it has a clear signature in Mössbauer spectra. Besides, the glass absorption edges undergo a clear blue shift, reflecting an increased band gap energy (1.96–2.28 eV). The decline in NBO bonds justifies this trend. Bewitchingly, the values of crystal field splitting are increased, while the values of Racah parameters are decreased. This trend is justified by the decline in NBO bonds and increases electron localization around Fe cations. Mössbauer spectra confirm the existence of Fe3+ in tetrahedral and octahedral sites, while Fe2+ exists in only a tetrahedral state. With increasing La2O3 content, the isomer shift of Fe3+ in tetrahedral sites changes to be 0.312–0.329 mm/s, while the isomer shift of octahedral Fe3+ is 0.424–0.456 mm/s. These findings coincide with optical data. While the isomer shift of tetrahedral Fe2+ is 0.902–0.911 mm/s. Our results of structural, optical and ligand field associated with Mössbauer spectra open more vistas toward the utility of these samples in the optics realm.

Tuning the magnetic properties of hard–soft Ba0.5Sr0.5Fe10Al2O19 and Ni0.1Co0.9Fe2O4 nanocomposites via one pot sol–gel auto combustion method for permanent magnet applications

Permanent magnets generate magnetic fields that can be sustained when a reverse field is supplied. These permanent magnets are effective in a wide range of applications. However, strategic rare-earth element demand has increased interest in replacing them with huge energy product (BH)max. Exchange-coupled hard/soft ferrite nanocomposites have the potential to replace a portion of extravagant rare earth element-based magnets. In the present, we have reported the facile auto combustion synthesis of exchange-coupled Ba0.5Sr0.5Fe10Al2O19 and Ni0.1Co0.9Fe2O4 nanocomposites by increasing the content of soft ferrite over the hard from x = 0.1 to 0.4 wt%. The XRD combined with Rietveld analysis reflected the presence of hexaferrite and spinel ferrite without the existence of secondary phases. The absorption bands from the Fourier transform infrared spectrum analysis proved the presence of M–O bonds in tetrahedral sites and octahedral sites. Rod and non-spherical images from TEM represent the hexaferrite and spinel ferrite. The smooth M–H curve and a single peak of the switching field distribution curve prove that the material has undergone a good exchange coupling. The nanopowders displayed an increase in saturation magnetization and a decrease in coercivity with the increases in the spinel content. The prepared nanocomposites were showing higher energy products. The composite with the ratio x = 0.2 displayed a higher value of (BH)max of 13.16 kJ m−3.

Promotion of oxygen evolution through the modification of Co-O bond in spinel NiCo2O4

The coordination environment of magnetic ions in transition metal oxides has a significant impact on the oxygen evolution reaction (OER) activity. Herein, we synthesized inverse spinel oxide NiCo2-xFexO4 (x = 0–1.5) on the nickel foam (NiCo2-xFexO4@NF) to explore the impact of Fe3+ ions doping in Co site on OER activity. The electrochemical results indicate that the introduction of Fe3+ ions drastically improved the OER performance for x ≤ 1.0. While the OER activity would decrease with further doping of Fe3+. The overpotential of 10 mA cm−2 decreased from 331 mV (NiCo2O4@NF) to 260 mV versus RHE (NiCoFeO4@NF) and lower Tafel slope (41.46 mV/dec) for OER in 1.0 M KOH electrolyte. Furthermore, there is a slightly decrease in overpotential after the stability test and the difference is not more than 2%. By comparing the structure of NiCoFeO4@NF and pristine NiCo2O4@NF, it was found that the doping of moderate amounts Fe3+ (x ≤ 1.0) would help to form the structure which can expose more active sites. Furthermore, XPS results indicate that transition from Co2+ to Co3+, the higher Co3+/Co2+ ratio contributes to good reducibility and oxygen mobility, and 3d state of Co3+ would generate strong hybridization with O 2p state. The EIS results imply that the incorporation of Fe can effectively improve the conductivity of materials and reduce the charge transfer resistance. Together with the magnetic properties, we found that Fe3+ ions replaced Co site in octahedral site with low spin state for x ≤ 1.0 implies beneficial effect for OER activity. While For x > 1.0, part of the Fe3+ ions locate in tetrahedron site with high spin state which show harmful effect for the OER activity.

Influence of annealing temperature on microstructure, magnetic and electrical properties of Ce doped cobalt ferrite nanoparticles

Cerium doped cobalt ferrite nanoparticles with chemical formula CoFe1·9Ce0·1O4 were synthesized at different annealing temperatures (600, 700, 800, 900 and 1000C°) via sol-gel auto-combustion method. Thermal analysis for sample annealed at 1000C° was examined through differential scanning calorimetry (DSC) and revealed the presence of exothermic peak at around 500C° attributed to crystallization of prepared nanoferrites. Structural analysis such as phase formation, crystallinity and morphology was investigated by x-ray powder diffraction (XRD) and high resolution transmission electron microscope (HRTEM). XRD study revealed higher dependence of grain size growth with annealing temperatures as compared to lattice parameter. HRTEM investigation confirmed that grains have almost uniform morphology with some agglomeration and confirmed values of lattice parameters and grain sizes calculated from XRD data. Magnetic hysteresis was studied by vibrating sample magnetometer (VSM) at room temperature with an applied field of 20 kOe. The results showed an increase in saturation magnetization and remanent magnetization with increasing of annealing temperature, whereas a decline in coercivity was observed. Distribution of cations at tetrahedral and octahedral sites was investigated using x-ray and magnetic parameters which confirmed the mixed spinel ferrite nature of samples. Dielectric properties were carried out at room temperature in the range 0.1Hz–3.0 MHz. Both dielectric constant and ac conductivity decreased with rising of annealing temperature. Variation of dielectric loss tangent, impedance, electric modulus and relaxation time with temperature were also investigated. The effect of annealing temperature on the structure and its impact on magnetic and dielectric properties has been examined and discussed.

Direct generation of high-valent iron-oxo species to eliminate oxytetracycline at circumneutral pH via paper mill sludge ash activating peroxymonosulfate

The excellent performance of high-valent iron-oxo species (FeIVO) in the degradation of pollutants by activating peroxymonosulfate (PMS) had attracted much attention. However, the generation and reaction mechanisms were still unclear. In this study, iron-rich paper mill sludge was used as a raw material for the first time to prepare iron-based catalysts with abundant octahedral FeIII sites (FeoctIII). The results showed that the highest content of FeoctIII was found in the paper mill sludge ash obtained by aerobic calcination at 800 °C (pmSA800), and the pmSA800 could exhibit excellent catalytic activity (0.4785 min−1) and stability during the oxytetracycline (OTC) degradation process. The characterization and density functional theory (DFT) calculations further indicated that the FeoctIII was the dominant active site for FeIVO production. PMS tended to be adsorbed on two adjacent FeoctIII sites to form a [FeoctIII-OSO2OO(H)-FeoctIII] complex with a two-site adsorption configuration. Subsequently, the OO and OH bonds in [FeoctIII-OSO2OO(H)-FeoctIII] broken by absorbing energy, generating FeIVO. It's worth noting that the Ca species of pmSA800 effectively stabilized the pH of the reaction solution, which ensured the stable and continuous production of FeIVO. This work provides a new idea and insight for preparing catalysts that could produce FeIVO active species.

The nephelauxetic function he: A tool to locate the emission of Mn4+ in oxides and fluorides

A semi-empirical method is introduced to estimate the emission energy of the Mn4+ ion in fluorides and oxides without using spectroscopic data as inputs. The method is based on the calculation of the nephelauxetic function he at the octahedral crystal sites occupied by the Mn4+ cations in the considered host lattices. Only structural data are required for this calculation. The model reproduces the experimental emission energy of Mn4+ in 51 tested fluorides and 101 tested oxides within ±300 cm−1 in 98% of the fluorides and within ±500 cm−1 in 85% of the oxides. The accuracy is lowered as the he value, i. e. the covalency of the Mn–O bonding, is raised.

Study of structural, X-ray photoelectron spectroscopy, Raman and temperature-dependent magnetic studies of NiFe2O4/CoCr2O4 nanocomposites

In recent years, cobalt chromites/nickel ferrites have been attractive candidates for significant applications as nanomagnets. In the present work, structural, electronic, vibrational and low-temperature magnetic properties of NiFe2O4, CoCr2O4, and NiFe2O4/CoCr2O4 nanocomposites were investigated. Refined XRD patterns and the Raman spectra confirm the formation of the pure crystalline spinel cubic phase. The estimated crystallite size is in the range of 14 - 29 nm. X-ray photoelectron spectroscopy (XPS) confirm the oxidation state of all elements present in the synthesized samples. The studies of the photoemission core level lines prove the cations distribution in the tetrahedral and octahedral sites with the expected valence states. The magnetic studies reveal the S-type hysteresis loops, confirming the ferrimagnetic nature. The remanent and saturation magnetization increase with increasing NiFe2O4 concentration and decrease with increasing temperature. The magnetization also increases with increase of crystallite size. The temperature-dependent magnetization curve of CoCr2O4 shows the ferrimagnetic phase transition at Curie temperature TC = 86 K. The performed density functional theory (DFT) calculations indicate a significant distribution of the density of states over the Fermi level in NiFe2O4/CoCr2O4 composites as compared to bare NiFe2O4 and CoCr2O4 materials, confirming the improved electronic properties. The overall magnetic analysis proved the magnetization enhancement by increasing x concentration.

Mn2+ doped SrSn(PO4)2 nanopowder for new novel LED material

In the current work, SrSn(PO4)2 with Mn2+ doped nanopowder was prepared by solid state reaction method at temperature 950 K. Mechanically, the equipped nanopowder was characterized by structural, spectral, optical, and luminescence investigations. Crystallite size, phase of the sample was explained by powdered XRD analysis. SEM and HR-TEM analyses provided information about the average particle size of nanopowder, while EDS analysis confirmed elemental composition. The selected area electron diffraction (SAED) pattern confirmed the sample crystalline nature by means of rings corresponding to its XRD planes. FTIR study was explained by fundamental symmetric and asymmetric modes of vibrations. Optical absorption spectrum exhibited the typical Mn2+ bands in visible region. EPR studies revealed the distorted octahedral site symmetry for Mn2+. PL spectrum showed less intense emission region. The evaluated CIE co-ordinate values indicate color precipitation and CCT value is greater than 5000k which reveals that the present Mn2+:STP is useful for warm light LED applications.

NiFe2O4 nanoparticles as highly efficient catalyst for oxygen reduction reaction and energy storage in supercapacitor

Nickel ferrite (NiFe2O4) nanostructures (NSs) were synthesized via a low-cost and reproducible co-precipitation method. The as-synthesized material was annealed at different temperatures to investigate electrochemical performances for oxygen reduction reaction (ORR) and energy storage capacity. The X-ray diffraction (XRD) pattern confirmed the cubic structure of NiFe2O4 (NF) NSs. The decreased agglomeration and increased particle size were observed by field effect scanning electron microscopy (FE-SEM) with annealing temperature. The presence of Ni–O and Fe–O bonds at tetrahedral and octahedral sites was confirmed by Fourier transform infrared (FTIR) spectroscopy. The electrochemical analysis studied using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) demonstrated that the NF NSs annealed at 900 °C exhibited impressive electrochemical activity with a specific capacitance of ∼136 F/g, outperforming samples synthesized at lower temperatures. Moreover, the electrode material displayed excellent long-term stability over 3000 cycles for ORR activity. The remarkable electrochemical performance of NF NSs at higher annealing temperatures highlights their potential for future energy storage and conversion devices.

Unveiling Local Electronic Structures of Manganese‐Doped Double Perovskites Red Emitters

AbstractOver the past few years, light‐emitting diodes (LEDs) have emerged as an efficient replacement for standard incandescent and fluorescent lamps, due to their superior efficiency, energy conservation, service longevity, reliability, and affordability. However, identifying a red emitter for white LEDs has presented significant challenges. This study seeks to synthesize and analyze a novel red emitter, investigating its potential use in white LEDs and indoor plant growth lighting. The Sr2Lu(Nb,Mn)O6 is manufactured employing the traditional high‐temperature solid‐phase method. The internal and external quantum efficiencies (IQE and EQE) of double perovskites reached 32.39% and 21.67%. The g value calculates to 2.146, which corroborates that the magnetic dipolar transitions of Mn4+ ions inhabit symmetric octahedral sites. First‐principles investigations are utilized to unveil local electronic structures. Emission spectra reveal a substantial broad red emission peak at 688 nm. The Tanabe–Sugano diagram is applied to understand the luminescence mechanism. Additionally, the evaluation of parameters such as the internal UV emission ratio, crystal field strength, and Racah parameters is conducted. The luminescent intensity of the Sr2Lu(Nb,Mn)O6 can still be maintained at 60% upon reaching a temperature of 423 K. The findings suggest that Sr2Lu(Nb,Mn)O6 offers a novel alternative for white LEDs and indoor plant growth lighting.

Unveiling electronic structure and magnetic properties of AFe2O4 (A = Co, Ni, Zn, and Mg): Synergizing experimentation with DFT investigation

This study presents the synthesis of nano-crystalline spinel ferrites AFe2O4 (A = Co2+, Ni+2, Zn+2, and Mg+2), through the sol-gel method, yielding crystallite sizes ranging from 12 to 28 nm. The variation in IR and Raman spectra due to M-O-M bonding supports the variation in lattice parameters. The magnetization measurements revealed that CoFe2O4 has a high saturation magnetization of ∼55 emu/g and coercivity of ∼1350 Oe, while ZnFe2O4 exhibited saturation magnetization value of ∼8 emu/g and coercivity of ∼16 Oe. In addition, the electronic structure calculated using DFT, which corroborated the antiparallel alignment of Fe ions in the tetrahedral and octahedral sites, validating the measured magnetic moments. Notably, the CoFe2O4 ferrite exhibited a higher squareness ratio than other ferrites, signifying its suitability as a magnetic material for audio-video recording.

Probing temperature-dependent magnetism in cobalt and zinc ferrites: A study through bulk and atomic-level magnetic measurements for spintronics

Spinel ferrites (MFe2O4) are integral to various industries, particularly spintronics, which utilizes the intrinsic spin of electrons as well as the electronic charge to develop devices that dictate spin-based transport, advancing new memory, logic applications, and improving magnetic storage technologies. These materials are valued for their exceptional optical, magnetic and electrical properties, and their easily tunable shape and size. This flexibility of spinel ferrites and their connection to the material’s magnetic behavior can be investigated by studying a range of spinel ferrite structures. In this study, the magnetic behaviors of cobalt ferrite (CFO) and zinc ferrite (ZFO) nanoparticles were examined using a vibrating sample magnetometer (VSM, bulk magnetometry) and X-ray Magnetic Circular Dichroism (XMCD, atomic magnetometry). The Rietveld refinement of XRD data supported single phase spinel structure, while X-ray Absorption Spectroscopy (XAS), particularly through the Co L-edge XANES analysis, detected both Co2+ and Co3+ ions in CFO, suggesting significant ferromagnetic behavior due to octahedral site occupation. In contrast, ZFO exhibited antiferromagnetic character, with Zn2+ ions in tetrahedral sites, and canted antiferromagnetism manifesting as a hysteresis loop below 300 K, potentially related to lattice distortions or strain. At the atomic scale, XMCD analysis, along with sum rules, estimated the average magnetic moments for cobalt and zinc ferrites to be 3.045 ± 0.1 (1.448 ± 0.1) and 0.657 ± 0.1 (2.12 ± 0.1) μB at temperatures of 300 K (90 K), respectively. However, VSM-based bulk measurements indicated magnetic moments of 2.566 (2.288) and 0.281 × 10−3 (0.6503 × 10−3) μB for CFO and ZFO, respectively, at the same temperatures. The observed variation between bulk and atomic-scale magnetic moments points to complex interstitial interactions within the spinel ferrite’s sublattices. This discrepancy between the atomic-scale and bulk magnetic moments suggests intricate interstitial interactions within the spinel ferrite’s sublattices. These insights into the structural and magnetic intricacies of spinel ferrite nanoparticles enhance our understanding, facilitating the design of cutting-edge spintronic devices.