Octahedral Sublattice Research Articles

The magnetic characteristics of spinel-type MnCo2O4 at low temperatures

We report the magnetic properties of spinel oxide MnCo2O4 at low temperatures which is prepared through the sol-gel reaction process. The XPS results suggest that Mn3+ atoms exist in the octahedral sublattice originally occupied by Co3+ atoms. Afterwards, the AC susceptibility was measured at various frequencies, confirming a spin glass behavior at low temperatures. Additionally, analysis of the hysteresis loops revealed the presence of the exchange bias effect in our sample. The coexistence of spin glass behavior and the exchange bias effect in MnCo2O4 is attributed to the competition between ferromagnetic and antiferromagnetic interaction. The disorders of magnetic atoms in the lattice will also provide synergy for these magnetic behaviors.

Correlated electron physics near a site-selective pressure-induced Mott transition in α-LiFe5O8

The Mott insulator-to-metal transition (IMT) driven by electron correlations has been among the main research topics in materials science over the past decades. The complex interplay between electronic and lattice degrees of freedom leads to various transition scenarios. Of particular interest may be the case of a transition involving the formation of complex phases comprising regions that differ significantly in their physical properties within the same material. Here, we present the results that advance the understanding of the IMT phenomenon, offering the documentation of a pure site-selective mechanism that is not complicated by any structural and spin transformation. Combining XRD, resistivity, Mössbauer and Raman spectroscopy measurements, we provide evidence for a pure pressure-induced Mott transition in α-LiFe5O8, characterized by site-selective delocalization of electrons, leading to the formation, above ~65 GPa, of a site-selective Mott phase consisting of metallic and insulating sublattices. We note that the electron delocalization in the partially disordered octahedral sublattice cannot be understood purely in terms of a Mott transition, the Anderson-Mott transition picture seems more adequate.

Competition between Cubic and Tetragonal Phase Induced Unusual Vertical Magnetization Shift and Exchange Bias in CoxMn3−xO4 (1 ≤ x ≤ 2) Spinel Nanoparticles

CoxMn3−xO4 (1 ≤ x ≤ 2) spinel nanoparticles synthesized through conventional coprecipitation technique exhibit the coexistence of tetragonal and cubic phases in the range of 1 ≤ x ≤ 1.5, while a pure cubic phase is observed for 1.75 ≤ x ≤ 2 at room temperature. Reduction in tetragonal phase fraction from 92 % for x = 1 to 47% for x = 1.5 is attributed to diminution of Jahn–Teller (J–T) active Mn3+ ions occupying the octahedral site of spinel lattice. X‐ray photoelectron spectroscopy confirms both +2 and +3 oxidation states for Co and Mn. Surprisingly, cubic and tetragonal phases exhibit magnetic transition, Tc1 and Tc2, corresponding to a paramagnetic to a high and low temperature ferrimagnetic state, respectively. Tetragonal phase induces high spontaneous (HSEB) and conventional (HCEB) exchange bias with unusually high vertical magnetization shift (VMS) than that of the pure cubic phase, shows maximum HCEB of 4.062 kOe for x = 1.5 and a VMS of 2.5 emu g−1 for x = 1. Such dependence of VMS and exchange bias on tetragonal to cubic phase ratio in CoxMn3−xO4 is demonstrated for the first time and interpreted based on the interaction between different arrangement of spins in tetrahedral and octahedral sublattice.

The Influence of Reaction Medium pH on the Structure, Optical, and Mechanical Properties of Nanosized Cu-Fe Ferrite Synthesized by the Sol-Gel Autocombustion Method

Nanoscale mixed ferrites with a spinel structure are highly versatile materials widely employed across diverse fields, including engineering, biomedicine, and ecology. This study explores the influence of pH on the structure, morphology, electrophysical, and mechanical properties of CuFe2O4 spinel, synthesized using the sol-gel self-combustion method. The investigation reveals that the pH level significantly impacts the structure formation, even at the gel formation stage, thereby shaping the subsequent structure and properties of the synthesized ferrite. X-ray diffraction (XRD) analysis demonstrates that the dominant phase (>90%) corresponds to the cubic spinel phase with the chemical formula CuFe2O4, belonging to the Fd3m space group. Notably, the pH of the reaction medium exerts a profound influence on the distribution of iron and copper ions within the octahedral and tetrahedral sublattices of the spinel structure. This variation in cationic distribution manifests in notable changes in the synthesized ferrite's magnetic, mechanical, and degradation properties. Furthermore, the study delves into the impact of the synthesized CuFe2O4 spinel as a photocatalyst for degrading organic dyes through the photo-Fenton process. It demonstrates that degradation efficiency is closely related to the ferrite's band gap width and particle size. This study aimed to determine how the pH of the reaction medium impacts the structure, morphology, optical, mechanical, and magnetic characteristics of the nanosized ferrites being synthesized. Furthermore, the synthesized materials were evaluated for their photocatalytic abilities in degrading organic dyes in water. The ferrite powders showcased remarkable dye degradation capabilities via the photo-Fenton process. Degradation efficiency largely hinged on the band gap width and the size of the particles. The most notable outcome was achieved with sample P1, which had particle sizes averaging 12.14 nm. By unraveling the complex relationship between pH, structure, and properties, this research enhances our understanding of the design and optimization of nanoscale mixed ferrites.

Study of the influence of gamma irradiation on ferrite-spinel monocrystals

The mechanisms of redistribution of metal ions and the formation of defects in ferrite spinel upon irradiation are complex and depend on a number of factors. Therefore, computer simulations and experimental studies are important for understanding the behavior of the physical properties of these materials under the influence of radiation. The development of new materials that can withstand radiation damage is of great importance for a range of applications, including solid state physics, nuclear physics, space research and medical applications. In this work, the effect of gamma irradiation on Co0,75Cu0,25Fe2O4 ferrite single crystals has been investigated. An earlier study using Mössbauer spectroscopy was carried out to determine the changes in the metal ion content in the sublattices of ferrite spinels. These changes affect the magnetic crystallographic anisotropy of the material [1]. Data can be found in the scientific literature that indicate that gamma irradiation leads to changes in the magnetic susceptibility of materials and to changes in the magnetization curve [2,3]. These changes in physical properties can be explained by redistribution of metal ions in octahedral and tetrahedral sublattices, since metal ions in sublattices have splitting of atomic levels.

Impact of Cd+2 substitutions on structural and mechanical properties of Co0.6Ni0.4-xCdxFe2O4 (0.00≤ x≤0.40) system

This article presents the structural and mechanical properties of Co0,6Ni0,4-xCdxFe2O4spinel ferrite nanoparticles. The as prepared samples were characterized by thermo-gravimetric differential thermal analysis to examine their phase transition. TGA/DTA analysis confirmed the reaction is endothermic in nature and the process completion temperature around 714.24oC is good for annealing the prepared ferrite powder. X-ray diffraction pattern revealed, Co0,6Ni0,4-xCdxFe2O4 have been well crystallized to spinel crystal structure. The average crystallite size ranging from 14.52nm to 16.92nm. FTIR spectra showed, two significant absorption bands (ν1 and ν2) in between 400 cm−1and 600 cm−1confirmed the spinel structured ferrites. Morphological observations revealed, the grain size of prepared ferrites lies in the range 0.85 to 0.21 μm. Raman spectra peak positions of both tetrahedral and octahedral sublattice shifted towards higher energy position.

Cationic redistribution induced magnetic properties of Zn2+ substituted MgFe2O4 spinel ferrite

The effect of Zn incorporation on the cationic redistribution and consequent magnetic properties of Mg1-xZnxFe2O4 (0.0 ≤ x ≤ 0.8) spinels are reported. The X-ray photoelectron spectroscopy and X-ray diffraction studies reveal mixed spinel structures with cations occupying both octahedral and tetrahedral sublattices. Raman measurements show increased structural disorder with increasing Zn-content and A1g mode splitting attributed to peaks of Zn2+, Mg2+, and Fe3+ ions. The isothermal magnetization data reveal a maximum of 102 emu/g at x = 0.4, accompanied by a minimum in the coercivity (∼28 Oe) and a downward shift of the transition in temperature for x > 0.4. The temperature-dependent dc-magnetic susceptibility analysis shows a shifting of the transition region from the paramagnetic phase into the ferrimagnetic phase towards the lower temperature side with increasing Zn concentration. These materials synthesized by the low-cost solid-state method might revisit understanding Zn2+-induced cationic exchange in MgFe2O4 and find applications as a potential soft-magnetic material.

Magnetic properties of Mn/Co substituted nano and bulk Ni–Zn ferrites: A comparative study

The present work shows the comparative studies on the magnetic properties of Ni0.4Zn0.6-xCoxFe2O4, (Ni–Zn–Co) and Ni0.4Zn0.6-xMnxFe2O4 (Ni–Zn–Mn) with x = 0.00 to 0.25 in steps of 0.05, ferrites synthesized by sol-gel autocombustion and conventional ceramic methods. Rietveld refinement data confirms the formation of single phase - spinel crystal structure in all the samples. The role of ferromagnetic dopants like Co and Mn on the structural, microstructural, magnetic characteristics such as Curie temperature (Tc), saturation magnetization and coercivity of NiZnFe2O4 ferrite are investigated. The influences of crystallite size obtained by using two different synthesis methods on different magnetic properties are highlighted. Continuous Tc increases have been noticed in both instances along with increasing dopant concentrations. However, compared to Ni–Zn–Mn ferrites, Ni–Zn–Co ferrites display greater Tc values. The experimental observed magnetic moments measured from vibrating sample magnetometer (VSM) are fitted with the theoretical data. The saturation magnetization values exhibit a marginal increase in the bulk form of the material as compared to its nanocrystalline counterparts. On the basis of distribution of cation and exchange interactions between magnetic cations at its tetrahedral and octahedral sublattices, the typical mechanisms accountable for the observed trends were elucidated. In addition, the dc-resistivity and dielectric loss are measured to show the application aspects of the materials in various potential device applications.

Zinc- doped nickel ferrite nanoparticles for ESR, hyperhtermia and thier cytotoxicity in mouse muscle fibroblast (BLO-11) and human breast cancer (MDA-MB-231) cell lines

Spinel structured nickel ferrite (NiFe2O4) nanoparticles (NPs) are used in catalysis, magnetic, and microwave electronic devices. To study the magnetic interplay between half and above-filled d-orbitals in spinel structured transition metal cations: Fe3+ (3d5), Ni2+ (3d8), and Zn2+ (3d10), narrow size distributed, well crystallined zinc substituted NiFe2O4 magnetic nanoparticles (MNPs) were synthesized by solvothermal reflux method. Structural, morphological, magnetic, magnetic hyperthermia, and cytotoxicity properties of Zn0.15Ni0.85Fe2O4 (code: ZN1), Zn0.35Ni0.65Fe2O4 (code: ZN2), and Zn0.45Ni0.55Fe2O4 (code: ZN3) NPs were systematically studied. Both X-ray diffraction and electron diffraction profiles confirmed that all synthesized samples were crystallined in a cubic spinel structure. Further, the formation of octahedral and tetrahedral ligands in spinel structure is confirmed by Fourier transformed infrared (FTIR) spectra. In addition, metal cations and oxygen anions oxidation states were determined from X-ray photoelectron spectroscopy (XPS). Quantification of metal cations present in all samples was done by X-ray energy dispersive spectra. Macroscopic magnetic properties of NPs were studied by magnetometer and microscopic magnetic properties were studied by electron spin resonance (ESR) spectra. Superparamagnetic hyperthermia (SPMH) properties of NPs were studied by adiabatic hyperthermia curves using an induction heater. Biocompatibility properties of all NPs were studied by cell viability-based cytotoxicity assay on (BLO-11) mouse muscle fibroblast and (MDA-MB-231) human breast cancer cell lines. The above studies revealed that Zn2+ substitution initially enhances saturation mass magnetization (Ms) of NiFe2O4 and then reduces Ms when Zn2+ concentration is> 30 % due to zero octahedral site preference energy of Zn2+ and reduced superexchange strength in octahedral sublattice. This influences magnetic hyperthermia and cytotoxicity properties of NPs and is described here.

Features of the Preparation of Ni-Doped Bismuth Tantalate Pyrochlore

The possibility of high-temperature solid-phase synthesis of Ni-doped bismuth tantalate pyrochlore, not only from the oxide compounds BiTaO4 and NiO but also using nickel chloride NiCl2 as a precursor, was shown for the first time. The concentration range of the formation of nickel pyrochlore Bi2NixTa2O9−δ (0.85 ≤ x ≤ 1.0) at an equal molar ratio of bismuth(III)/tantalum(V) ions was determined. This indicates that the pyrochlore structure may be stable at 20–33% vacant bismuth sublattice. The influence of non-stoichiometric composition relative to bismuth and tantalum, by the example of Bi2±xNiTa2O9−δ and Bi2NiTa2−xO9−δ (x ≤ 0.5) compositions, on the phase composition of ceramics was studied. X-ray powder diffraction phase analysis of Bi2Ni1+yTa1.75−yO9−δ samples made it possible to determine the solubility limit of nickel ions in the tantalum sublattice. It was shown that the molar ratio of metal atoms (Ta, Ni) in the B2O6 (B-Ni(II), Ta(V)) octahedral sublattice of mixed pyrochlores is also limited.

Stoichiometry driven tuning of physical properties in epitaxial Fe3-xCrxO4 thin films

Tuning magnetic and electronic transport properties in spinel oxides requires a faithful description between chemical composition and cation site-occupation. Here this challenge is addressed using Fe3-xCrxO4 thin films grown by oxygen-assisted molecular-beam epitaxy within a wide range of composition (0.0 ≤ x ≤ 1.2). Spectroscopic measurements (e.g., X-ray magnetic circular dichroism), refined by theoretical simulations (e.g., crystal field multiplet), are performed to establish a quantitative link between chromium content, Fe2+/Fe3+ site-occupation and macroscopic physical properties of the layers. It is found that Fe3-xCrxO4 thin films (i) delay the transition from inverse to normal spinel configuration with increasing chromium content and (ii) promote collinear spin structure, at odds with bulk material. As a result, strong antiferromagnetic interactions are preserved between spins in tetrahedral and octahedral spinel sublattices, so that chromium-rich thin films exhibit Curie temperatures above room temperature and higher magnetization. Electron hopping is also favored by this singular cation distribution and electronic band gap is smaller than expected for these thin films. The cation site-occupation is therefore a key feature to consider for applications of Fe3-xCrxO4 thin films in spintronics and photocatalysis, as it enables manipulation of magnetic properties (Curie temperature and magnetization) and band gap engineering.

Structure and magnetism of electrospun porous high-entropy (Cr1/5Mn1/5Fe1/5Co1/5Ni1/5)3O4, (Cr1/5Mn1/5Fe1/5Co1/5Zn1/5)3O4 and (Cr1/5Mn1/5Fe1/5Ni1/5Zn1/5)3O4 spinel oxide nanofibers.

High-entropy oxide nanofibers, based on equimolar (Cr,Mn,Fe,Co,Ni), (Cr,Mn,Fe,Co,Zn) and (Cr,Mn,Fe,Ni,Zn) combinations, were prepared by electrospinning followed by calcination. The obtained hollow nanofibers exhibited a porous structure consisting of interconnected nearly strain-free (Cr1/5Mn1/5Fe1/5Co1/5Ni1/5)3O4, (Cr1/5Mn1/5Fe1/5Co1/5Zn1/5)3O4 and (Cr1/5Mn1/5Fe1/5Ni1/5Zn1/5)3O4 single crystals with a pure Fd3̄m spinel structure. Oxidation state of the cations at the nanofiber surface was assessed by X-ray photoelectron spectroscopy and cation distributions were proposed satisfying electroneutrality and optimizing octahedral stabilization. The magnetic data are consistent with a distribution of cations that satisfies the energetic preferences for octahedral vs. tetrahedral sites and is random only within the octahedral and tetrahedral sublattices. The nanofibers are ferrimagnets with relatively low critical temperature more similar to cubic chromites and manganites than to ferrites. Replacing the magnetic cations Co or Ni with non-magnetic Zn lowers the critical temperature from 374 K (Cr,Mn,Fe,Co,Ni) to 233 and 105 K for (Cr,Mn,Fe,Ni,Zn) and (Cr,Mn,Fe,Co,Zn), respectively. The latter nanofibers additionally have a low temperature transition to a reentrant spin-glass-like state.

Atomic-scale observation of calcium occupation in spinel cobalt ferrite towards the regulation of intrinsic magnetic properties.

Spinel ferrites have drawn intensive attention because of their adjustable magnetic properties by ion doping, among which calcium (Ca) is an essential dopant that is widely employed in massive production. However, its exact lattice occupation and relationship with intrinsic magnetic properties remain unclear. Here, we successfully prepared Ca-doped cobalt ferrite (CoFe2O4) nanoparticles by electrospinning. Ca2+ is observed to occupy both the tetrahedral Fe site and the octahedral Co site using spherical aberration correction transmission electron microscopy (TEM) and prefers to occupy the octahedral site at a high doping level. Such dual occupation behavior affects the tetrahedral and octahedral sublattices differently, resulting in nonmonotonic saturation magnetization variation, reduced magnetocrystalline anisotropy and negative magnetization in the zero field cooling (ZFC) process. By controlling the Ca doping amount, increased saturation magnetization and reduced coercivity can be obtained simultaneously. Our findings establish the relationship between the atomic-scale structural change and the macroscopic magnetic properties of spinel ferrites, promoting the development of new ferrite materials.

Antisite Defects and Chemical Expansion in Low‐damping, High‐magnetization Yttrium Iron Garnet Films

AbstractYttrium iron garnet is widely investigated for its suitability in applications ranging from magneto‐optical and microwave devices to magnonics. However, in the few‐nanometer thickness range, epitaxial films exhibit a strong variability in magnetic behavior that hinders their implementation in technological devices. Here, direct visualization and spectroscopy of the atomic structure of a nominally stoichiometric thin film, exhibiting a small damping factor of 3.0 ⋅ 10−4, reveals the occurrence of Y‐excess octahedral antisite defects. The two‐magnon strength is very small, Γ0≈10−6 Oe, indicating a very low occurrence of scattering centers. Notably, the saturation magnetization, 4πMs=2.10 (±0.01) kOe, is higher than the bulk value, in consistency with the suppression of magnetic moment in the minority octahedral sublattice by the observed antisite defects. Analysis of elemental concentration profiles across the substrate‐film interface suggests that the Y‐excess is originated from unbalanced cationic interdiffusion during the early growth stages.

A DFT study of Mn3O4 Hausmannite thin films supported on coinage metals

Mn3O4 Hausmannite thin films supported on (Cu, Ag, Au) coinage metals have been studied for the first time by means of DFT calculations. The different lattice and ionic match at the interface with the metal support gives raise to different type of interactions. On copper, Mn3O4 (110) films subject to tensile strain strongly adhere to the metal surface, undergoing a remarkable structural change. On the contrary, Mn3O4 (001) films adhere weakly to Cu (111) and Au (111), where the structural match is unfavourable, and strongly on Ag(100), where the lattice is commensurate and epitaxial films can grow.A negative charge flow from the support to the film is reported, in particular when strong bonds at the interface are formed. This causes the reduction of the film and the subsequent increase in the magnetic moments of some metal ions in the octahedral sublattice. The reduced centres are prevalently located at the film surface.The ferrimagnetic ordering is different in supported films exposing the (001) or the (110) face.

Terahertz-driven magnetization dynamics of bismuth-substituted yttrium iron-gallium garnet thin film near a compensation point

Magnetization dynamics of bismuth-substituted yttrium iron-gallium garnet film $({\mathrm{Y}}_{3\ensuremath{-}z}{\mathrm{Bi}}_{z})[{\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}][{\mathrm{Fe}}_{3\ensuremath{-}y}{\mathrm{Ga}}_{y}]{\mathrm{O}}_{12}$ has been studied using a terahertz pump--optical probe spectroscopy. Two magnetic modes are observed whose frequencies intersect at a magnetization compensation point. The experimental dependence of the excited modes on terahertz pulse polarization, an external magnetic field and the temperature are analyzed. The theoretical description based on symmetry and the Lagrangian formalisms is proposed. Magnetic modes crossing is explained as interplay between exchange and anisotropy energies equally contributing near the compensation point. Simulations based on the Landau-Lifshitz-Gilbert equations show that a difference in magneto-optical susceptibilities of tetrahedral and octahedral iron sublattices can substantially enhance the sensitivity to the magnetic modes.

Cationic redistribution induced spin-glass and cluster-glass states in spinel ferrite

The effect of the cationic redistribution on the complex spinel structure and magnetic properties were investigated in ${\mathrm{Zn}}_{0.7}{\mathrm{Cu}}_{0.3}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ ferrite. X-ray photoelectron spectroscopy and x-ray diffraction studies revealed that the system exhibits a mixed spinel structure with ${\mathrm{Fe}}^{3+}, {\mathrm{Zn}}^{2+}$, and ${\mathrm{Cu}}^{2+}$ occupying both tetrahedral and octahedral sublattices. The DC magnetization results revealed the absence of long-range magnetic order in the system. Furthermore, the AC susceptibility data analysis using dynamic scaling laws suggests that the system exhibits magnetic relaxation below two different temperatures: (i) a spin-glass--like transition at low temperature ($\ensuremath{\sim}49.2\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) with critical exponent 10.3 and spin-flip time $\ensuremath{\sim}{10}^{\ensuremath{-}11}\phantom{\rule{0.28em}{0ex}}\mathrm{s}$, and (ii) a cluster-glass--like transition at higher temperature ($\ensuremath{\sim}317\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) with critical exponent 4.6 and spin-flip time $\ensuremath{\sim}{10}^{\ensuremath{-}10}\phantom{\rule{0.28em}{0ex}}\mathrm{s}$. The existence of glassy behavior and magnetic memory effects below the spin-glass transition temperature proves that the system is in nonequilibrium dynamical state. The coexistence of spin-glass and cluster-glass along with the thermal hysteresis between these two transitions could widen the technological applications of these systems.

Thermodynamic modeling of the Pd–Zn system with uncertainty quantification and its implication to tailor catalysts

Pd–Zn intermetallic catalysts show encouraging combinations of activity and selectivity on well-defined active site ensembles. Thermodynamic description of the Pd–Zn system, delineating phase boundaries and enumerating site occupancies within intermediate alloy phases, is essential to determining the ensembles of Pd–Zn atoms as a function of composition and temperature. Combining the present extensive first-principles calculations based on density functional theory (DFT) and available experimental data, the Pd–Zn system was remodeled using the CALculation of PHAse Diagrams (CALPHAD) approach. High throughput modeling tools with uncertainty quantification, i.e., ESPEI and PyCalphad, were incorporated in the phase analysis. The site occupancies across the γ phase composition region were given special attention. A four-sublattice model was used for the γ phase owing to its four Wyckoff positions, i.e., the outer tetrahedral (OT) site 8c, the inner tetrahedral (IT) site 8c, the octahedral (OH) site 12e, and the cuboctahedral (CO) site 24g. The site fractions of Pd and Zn calculated from the present thermodynamic model show the occupancy preference of Pd in the OT and OH sublattices in agreement with experimental observations. The force constants obtained from DFT-based phonon calculations further supports the tendency of Pd occupying the OH sublattice compared with the IT and CO sublattice. The catalytic ensembles changing from Pd monomers (Pd1) to trimers (Pd3) on the surface of γ phase are attributed to the increase of Pd occupancy in the OH sublattice.

Local Ionic Displacements and Polarization at the Paraelectric‐Ferroelectric Heterointerface: Effect of Octahedral Distortion

AbstractAt the ferroelectric ABO3 perovskite heterointerface, the broken translational symmetry significantly alters the octahedral network and cation sublattices. Experimentally revealing the interaction between the polarization and atomic structure parameters is beneficial not only for understanding the novel physical phenomena but also for realizing exotic physical functionalities at the materials surface science. Here, it is demonstrated that the induced polarization can be realized by the cooperative interaction between the octahedral distortion and the cation sublattices at the paraelectric‐ferroelectric heterointerface in the (K,Na)NbO3 epitaxial thin film. It is found that the cation–cation displacement scales with the tetragonality of the perovskite unit cell but not with the polarization, which is minimal in the substrate but increases substantially in the thin film. Nevertheless, the oxygen octahedral distortion in the substrate, accompanied by octahedral rotation, is stronger than that in the film, resulting in a translated and stable polarization across the interface. These results demonstrate the octahedral network plays a significant role in the ferroelectric polarization and can also greatly advance the understanding of the heterointerface science for ferroelectrics.

Structural, Degree of Inversion, and Magneton Number Studies on Fe3+‐Substituted MAl2O4 (M = Ni, Cu, Zn) Spinel Powders: The Evidence for Local Site Exchange of Cation and Magnetization Increment

Nanocrystalline Fe‐substituted metal aluminates, MFe x Al2−x O4 powders (M = Ni2+, Cu2+, and Zn2+) with different Fe3+ ion concentrations (x = 0, 0.5, 1.0, 1.5, and 2), are successfully synthesized by the sol–gel auto combustion method. Characterization of the calcined samples is carried out using X‐ray diffraction (XRD), synchrotron Extended X‐ray Absorption Fine Structure (EXAFS), and vibrating sample magnetometer (VSM) measurements. The XRD results confirm the formation of single‐phase spinel structure with Fd‐3m space group of all samples. The EXAFS spectra illustrate the main translocation trends in the trivalent and divalent ions between the tetrahedral and octahedral sublattices. When XRD Rietveld refinement, Williamson–Hall analysis, and EXAFS curve‐fitting analysis are applied to the data, the precise structural parameters, degree of inversion, and cation site occupancy are obtained. Furthermore, the Fe‐substituted samples show intense increase in the saturation magnetization with the increasing of Fe3+ ion concentrations. This occurrence is due to the rise in the net magnetic moment of the modified aluminates which took place as the distribution of the cations within the structure underwent changes. It is possible to explain the variation observed in the magneton number in the context of Fe3+ content through the application of Néel's collinear spin ordering model.