Single Spinel Structure Research Articles

Effect of divalent metal ions substitution on structural and magnetic properties of Li0.25Mn0.5-xMxFe2.25O4 (M = Co2+, Ni2+, Cu2+) spinel ferrites

In the existing study, substitution of different divalent metal ions in Li0.25Mn0.5-xMxFe2.25O4 (where, M = Co2+, Ni2+, Cu2+; x = 0.0, 0.1, 0.3 and 0.5) was performed to improve the magnetic properties. Their structural and magnetic features were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). XRD analysis proved the presence of single phase cubic spinel structure in all prepared compositions. The lattice parameter decreased linearly with increasing doping concentrations. The crystallite size values vary from 60 to 101 nm. VSM studies revealed that saturation magnetization values of Li0.25Mn0.5-xMxFe2.25O4 were strongly affected by different metal ions substitutions, which is credited to the cationic arrangement on the lattice sites. The change in the magnetization with metal substitution was discussed by using Neél's two-sublattice model. Among the three investigated series, Li0.25Mn0.5-xCoxFe2.25O4 ferrite revealed a synergistic effect in improving the magnetic properties making it suitable for applications in microwave devices and magnetic recording media. The initial permeability μi was measured at elevated temperatures from 300 up to 890 K. The composition Li0.25Mn0.4Ni0.1Fe2.25O4 gave the highest value of initial permeability, indicating the material potential utility in TV deflection yokes. Curie temperature increased with the replacement of manganese ions by different metal ions. In general, the replacement of different divalent transition metal ions plays an important role in changing the structural and magnetic properties of Li0.25Mn0.5Fe2.25O4 ferrites.

Preparation and characterization of Ni0.6CoxMn2.4−xO4 (0.2 ≤ x ≤ 1.4) NTC ceramics with low resistivity and high B value

The effects of Co content on the phase structure, micromorphology and electrical performance of Ni0.6CoxMn2.4−xO4 ceramics were studied using transmission electron microscope (TEM), X-ray powder diffractometer (XRD), scanning electron microscope (SEM), energy-dispersive spectrometer (EDS) and resistance/temperature measurements. TEM and high angle annular dark field (HAADF)-mapping results show that the calcined powders were nano-sized and the elements were uniformly distributed. For x < 0.98, the ceramics exhibited single cubic spinel structure. Our SEM–EDS results confirm that a rock-salt phase (Ni,Co)O is formed when 0.98 ≤ x ≤ 1.4. The lattice parameter of the spinel phase decreases with increasing Co content. The room-temperature resistivity of the ceramics decreases from 1100 to 219 Ω cm and then increased to 325 Ω cm as Co was added, while the B value decreased slightly from 3588 to 3030 K. The Ni0.6CoxMn2.4−xO4 ceramics are promising negative temperature coefficient materials for temperature monitoring in electric vehicles owing to their low resistivity and high B values.

The Possibility of Utilizing the Composite Ferrites as Core Material for the Fabrication of Multilayer Chip Inductors

This work mainly focuses on the investigation carried out on MgCuZn and NiCuZn ferrites which are widely employed for many electronic applications, they are very promising candidate for microinductor applications particularly to produce multilayer chip inductors (MLCIs) due to their excellent properties. Ferrite composites powder of Mg0.6Cu0.1Zn0.4Fe2O4 and Ni0.35Cu0.05Zn0.6Fe2O4 powder were synthesized by conventional ceramic double sintering technique. After being mixed with different volume fractions, a series of novel and dense composites with generic formula (1-X) Mg0.6Cu0.1Zn0.4Fe2O4 + (X) Ni0.35Cu0.05Zn0.6Fe2O4 were obtained in which X varies from 0.0 to 1.0. The presence of phases was confirmed by X-ray diffraction studies which confirms the formation of single phase cubic spinel structure and the grain size was estimated using SEM micrographs. In search of the suitable ferrite materials for microinductor applications, assuming that the ferrite composites would yield enhanced magnetic properties, an investigation is carried out on the composite ferrites and on the pure. To investigate the magnetic and electrical properties which studies were carried out in the temperature range 30 to 360oC and within the frequency range 100 Hz to 1MHz. These studies revealed that these ferrites possess good electromagnetic properties and can be exploited as core material for microinductor applications.

Effect of annealing temperature on the structural, dielectric and electric properties of $$\hbox {Ni}_{{0.7}} \hbox {Cd}_{0.3}\hbox {Fe}_{2}\hbox {O}_{4}$$ ferrites

A composition of Ni $$_{{0.7}}\hbox {Cd}_{{0.3}}\hbox {Fe}_{{2}}\hbox {O}_{{4}}$$ (NCF) ferrite nanoparticles was synthesized by a sol–gel auto-combustion technique. The particles in powder form were annealed at 550 and 700 $$^{\circ }\hbox {C}$$ to study the structural, dielectric and electric properties of NCF by using X-ray diffraction (XRD), field emission scanning electron microscopy, impedance and modulus spectroscopy. XRD patterns confirmed the single phase cubic spinel structure of the sample. The average crystallite size of NCF was found to be 17 nm at 550 $$^{\circ }\hbox {C}$$ and 31 nm at 700 $$^{\circ }\hbox {C}$$ , respectively. The variation in complex dielectric constant, loss tangent and impedance along with the modulus properties of NCF with frequencies was observed at room temperature because of their size and annealing temperature. Notably, dielectric dispersion of the materials was observed at low frequencies because of Maxwell–Wagner interfacial polarization. The impedance and modulus spectroscopy were used to investigate the electric properties of the materials, which revealed the increase in grain and grain boundary resistance with annealing temperature. A non-Debye type of relaxation in the materials was evidenced through the Cole–Cole study of impedance and modulus spectra.

Effect of Gd3+ substitution on proton relaxation and magnetic hyperthermia efficiency of cobalt ferrite nanoparticles

In this study, Gadolinium substituted Cobalt Ferrite nanoparticles (CoFe2-xGdxO4, 0 ≤ x ≤ 0.4) were prepared via hydrothermal route using triethylamine as reducing agent at 180°C for 12 h. X-ray diffraction studies revealed the single phase cubic spinel structure for both Cobalt ferrite (CF) and Gadolinium substituted Cobalt Ferrite (CFG) nanoparticles (x ≤ 0.24). An increase in the Specific absorption rate (SAR) was observed with increase in Gd concentration. Further with increase in the molar concentration (x > 0.24), gadolinium hydroxide was observed as the secondary phase, which was also confirmed by the Gd–O stretching vibrations observed in Fourier transform Infrared spectroscopy. The evolution of Gadolinium hydroxide showed a strong influence in the relaxivity (r1) and hyperthermia potential. Field emission scanning electron microscopy revealed that CF and CFG (x ≤ 0.24) nanoparticles were spherical in nature with particle size ranging from 10 to 25 nm, whereas the particle size increases above 30 nm for CFG (0.3 ≤ x ≤ 0.4) nanoparticles along with the presence of columnar shaped particles. Magnetic measurements confirmed the pseudo single domain, ferri-magnetic nature of CF and CFG nanoparticles. The magnetization data revealed a change in direction of magnetization towards easy axis with increasing Gd concentration. The orientation of magnetization direction towards easy axis had induced change in the hyperthermia potential. Proton relaxation studies of CF and CFG nanoparticles revealed that there is a strong interaction between the relaxivities r1 and r2. The specific absorption rate of CF and CFG nanoparticles were observed to be in the range from 91.49 W g−1 to 232.17 W g−1 at applied Hf of 4.19 × 109 Am−1 s−1.

Hyperthermic evaluation of oleic acid coated nano-spinel magnesium ferrite: Enhancement via hydrophobic-to-hydrophilic surface transformation

Abstract The work reports, enhancement in colloidal stability and hyperthermia efficiency of nano-spinel magnesium ferrite (MgFe2O4) by hydrophobic-to-hydrophilic surface transformation via oleic acid (OA) coating. The nano-spinel structured MgFe2O4 was prepared by the auto-combustion assisted sol-gel route and consequently, its surface was coated by OA. The uncoated and coated MgFe2O4 were portrayed by various physicochemical characterizations. The XRD analysis assured the unchanged single phasic cubic spinel structure and nanocrystalline nature of both the samples. FT-IR spectral analysis indicated the spinel belonging two vibrational stretching modes and OA attachment over the MgFe2O4 core. FE-SEM images revealed the nano-metric spherical type grain-morphology and visualization of OA coating. The drastic diminishment in contact angle values signifies hydrophobic to hydrophilic surface transition. M − H plots revealed the superparamagnetic appearance of uncoated and coated samples. Physisorption analysis showed the elevated surface area and pore size values. Zeta potential and DLS study displayed the enhancement in fluidic dispersion and hydro-dynamic size. The nano-particle concentration (2–10 mg/mL) dependent hyperthermia analysis was carried out for both the samples. Cell viability studies confirmed the improvement in the bio-friendly nature of MgFe2O4 via OA coating. All the outcomes show the superiority of the surface transformed MgFe2O4 nanoparticles in nano-magnetic hyperthermia treatments.

Structural, optical, elastic and magnetic properties of Ce and Dy doped cobalt ferrites

Abstract The CoCexDyxFe2-2xO4 (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05) have been prepared by sol-gel auto-combustion technique. The structural result confirmed the formation of single phase cubic spinel structure showed by XRD. Crystallite size obtained from the XRD is in the range of 24–28 nm, whereas particle size obtained from the transmission electron microscopy is in the range of 20–30 nm. It is also found that the cation distribution of CoCexDyxFe2-2xO4 resulted in the Fe3+ and Co ions occupy both tetrahedral A-site and octahedral B-site, whereas Ce and Dy cation distributed in both of them. The photoluminescence (PL) analysis reveals that all prepared samples contain four bands; (i) peak centered at 412 nm corresponding to ultraviolet (UV) band i.e. near band edge emission, (ii) a high intensity peak centered at 434 nm belonging to violet band, (iii) a low intensity and sharpness peak positioned at 466 nm refers to blue band, and (iv) a broad and very low intensity peak observed at 502 nm assigned to green band. FTIR results of the prepared samples showed that two vibration bands between 600 cm−1 and 400 cm−1 belonging to the stretching vibration of tetrahedral metal-oxygen bond (vA) and stretching vibration of octahedral site (vB) respectively. Mossbauer spectroscopy has also been performed to investigate the hyperfine structure of undoped, Ce and Dy co-doped cobalt nano ferrites. The higher values of MS and Hhf for x = 0.01 composition can be attributed to the occupation of Dy3+ ions in octahedral site whereas the Ce3+ ions occupied to tetrahedral site.

Facile preparation of single phase high-entropy oxide nanocrystalline powders by solution combustion synthesis

Abstract High-entropy oxides (HEOs), due to their excellent physicochemical properties, have attracted extensive attention. In this work, the solution combustion synthesis approach was applied to prepare a series of porous single-phase HEO nanocrystalline powders. Equiatomic (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O, (Cr0.2Fe0.2Mn0.2Mg0.2Zn0.2)3O4 and (Ce0.2La0.2Pr0.2Sm0.2Y0.2)O2 were successfully obtained. While the former two could be stabilized into single rock-salt (Fm-3m) and spinel (Fd-3m) structures, the latter could be synthesized to have either CaF2-type (Fm-3m) or CaF2-related-type (Ia-3) structure depending on synthesis temperature. Furthermore, their chemical and microstructural homogeneity was further confirmed.

Mechanical behavior, enhanced dc resistivity, energy band gap and high temperature magnetic properties of Y-substituted Mg–Zn ferrites

We report the synthesis of Y-substituted Mg–Zn [Mg0.5Zn0.5Y x Fe2−x O4 (0 ≤ x ≤ 0.05)] ferrites using conventional standard ceramic technique. The samples were characterized by x-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM), FTIR spectroscopy, UV–Vis spectroscopy and quantum design physical properties measurement system (PPMS). XRD patterns confirm the single phase cubic spinel structure up to x = 0.03 and appearance of a secondary phase of YFeO3 for higher Y contents. FESEM images depict the distribution of grains and EDS spectra confirmed the absence of any unwanted element. Completion of solid state reaction and formation of spinel structure has been revealed from FTIR spectra. The FTIR data along with lattice constant, bulk density and porosity were further used to calculate the stiffness constant (C ij), elastic constant and Debye temperatures. Mechanical stability of all studied compositions is confirmed from C ij using Born stability conditions. Brittleness and isotropic nature are also confirmed using Poisson’s ratio and anisotropy constants, respectively. The enhancement of dc electrical resistivity (105Ω cm to 106Ω cm) with Y content is observed. The energy band gap (increased with Y contents) is found in good agreement with dc electrical resistivity. Ferrimagnetic to paramagnetic phase change has been observed from the field dependent high temperature magnetization curves. The magnetic moments and saturation magnetization were found to be decreased with increasing temperature. The Curie temperature (Tc) has been measured from temperature dependent magnetic moment (M-T) and initial permeability (μ′i-T) measurements and found to be in good agreement with each other. Decrease in Tc with Y content is due to redistribution of cations and weakening of the exchange coupling constant. The magnetic phase transition has been analyzed by Arrott plot and found to have second order phase transition. The dc resistivity endorses the prepared ferrites are suitable for high frequency and high temperature magnetic device applications as well.

Influence of antimony substitution on structural, magnetic and optical properties of cadmium spinel ferrite

In this present work, antimony-substituted cadmium ferrites with formula CdSbxFe2−xO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5) have been synthesized using the ceramic route. The structural, surface morphological, magnetic and optical properties have been investigated using X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, vibrating sample magnetometer and UV–visible spectroscopy, respectively. XRD confirms the single cubic spinel structure of antimony-substituted cadmium ferrites. The lattice parameter increases due to the replacement of Fe+3 (0.64 A) ions with Sb+3 (0.76 A). FTIR gives the main vibrational band that lies in the range of 400–600 cm−1 which might be due to the stretching vibration of oxygen and metal ions, confirming the formation of spinel ferrite. The saturation magnetization decreases and coercivity increases as the concentration of non-magnetic antimony ion increases. The optical band gap energy decreases with increasing the concentration of antimony ions.

Effect of Cd2+ doping on structural, morphological, optical, magnetic and wettability properties of nickel ferrite thin films

Ni1-xCdxFe2O4 (0.0 ≤ x ≤ 1.0 in step of 2) spinel ferrite thin films have been synthesized by spray deposition technique. The prepared films were characterized by X-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy, UV–vis spectroscopy, Photoluminescence and contact angle measurement studies. The analysis of XRD pattern reveals broad peaks exhibiting a single phase cubic spinel structure. The crystallite size obtained from Scherrer’s formula varies between 8−24 nm confirming the nanocrystalline nature. Metal cation active vibration modes, metal oxygen stretching and bending vibrations were confirmed through the Raman analysis. The FE-SEM shows that the formation of spherical agglomeration and grain size are found to be in the range of 19–38 nm. The elemental compositions of the prepared thin films were studied by EDS. The energy band gap decreases from 1.86 to 2.11 eV with increase in Cd2+ content x calculated by using UV–vis data. The Photoluminescence study showed the characteristic near-band-edge emission of presently investigated films samples at around 710 nm. All films are hydrophilic in nature conformed by contact angle measurement.

Effect of calcination temperature on optical, magnetic and dielectric properties of Sol-Gel synthesized Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0–0.8)

The Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6 & 0.8) nanomaterials were prepared via sol-gel technique. These samples were calcined at three different temperatures (T) such as 400, 450 and 500 °C/5 h. Furthermore, the X-ray diffraction (XRD) patterns of all the calcined samples revealed the single phase cubic spinel structure. The lattice constants (a = b = c) were noticed to be increasing with increase of ‘x’. The grain shape, size and distribution of x = 0.0–0.8 contents were analyzed using field emission electron microscope (FESEM). The x = 0.2 content provided higher optical band gap energy (Eg) value than the remaining contents. Furthermore, the magnetization versus magnetic field (M − H) curves indicated the superparamagnetic nature of x = 0.0–0.8 contents. The high saturation magnetization (Ms) was noticed for x = 0.4 and 0.6 contents. In addition, the distribution of cations like Ni+2, Mg+2, Zn+2, Fe+3 and Fe+2 was performed between the tetrahedral (A) and octahedral (B) sites. The frequency dependence of dielectric constant (ε′), dielectric loss (ε") and ac-electrical conductivity (σac) was investigated as a function of composition. Moreover, the temperature variation of ε′ showed the decreasing trend of dielectric transition temperature (Te) with increase of ‘x’. The high ε′ of 163.1 (at 1 MHz) was noticed at x = 0.2 content calcined at 500 °C. Using the power law fit applied to the log σac-log ω plots, the dc-electrical conductivity (σdc) and exponent (n) parameters were calculated.

High-performance chromite by structure stabilization treatment

Chromite is an important raw material applied in refractories. Efforts have been made to obtain high-performance chromite by adding MgO and Al2O3 from the viewpoint of structure optimization. In order to explore the effect of Al2O3 and MgO on the structure, two formulas, i.e., Mg-rich and Al-rich ones, were selected. The phase and microstructure development of samples heated in the temperature range of 1200–1600 °C were studied by X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry. MgO and Al2O3 added have diffused into chromite successfully by heat treatment. MgO diffuses into chromite, occupying the tetrahedral vacancies caused by the diffusion and oxidation of Fe2+ ions to stabilize the structure. Al2O3 diffuses into the surface layer of chromite, forming spinel-sesquioxide structure. Al-rich sample which has spinel-sesquioxide structure shows better corrosion resistance toward fayalite slag than Mg-rich sample which has single spinel structure by blocking the interdiffusion between Fe2+ ions in fayalite slag and Mg2+ ions in chromite.

X-Ray Diffraction and Structural Study of Cu0.7+x Cd0.3ZrxFe2-2xO4 (x = 0.1) Mixed Spinel System

The crystal structure and lattice parameters of the Cu and Fe co-substituted disordered spinel series Cu0.7+x Cd0.3Zrx Fe2-2xO4 are investigated by means of X-ray diffraction (XRD) at room temperature(300K) and SEM results. The crystalline ferrite has been prepared by a modified Sol-Gel method. The analysis of XRD pattern suggests that the prepared Cu0.7+x Cd0.3Zrx Fe2-2xO4 (x = 0.1) spinel ferrite possesses single phase cubic spinel structure. The intense peaks of the XRD pattern were used to determine the average crystalline size. The crystalline size obtained from XRD data using Scherrer formula is of the order of ~0.5nm. So far no one has reported any crystalline size smaller than 0.5 nm. The calculations from SEM results agreed within the limits. In present work the lattice parameter, particle size, lattice strain and studied with the different concentrations (x = 0.1 to 0.4). The results were compared with ceramically prepared samples.

Physical and spectral studies of Mg-Zn ferrite prepared by different methods

Nano particle of Magnesium Zinc ferrite (Mg1-xZnxFe2O4, where x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been prepared by using the standard ceramic technique and mechanical ball milling method. X-ray diffraction (XRD), (IR) spectra, and scanning electron microscope (SEM)were carried out to characterize the prepared samples. Single phase cubic spinel structure with a main peak (311) at 2Ɵ = 34o was observed for all studied samples. The crystallite size was found to be within the range 37–65 nm. From IR spectra, the absorption bands at 605 cm-1 (ν1) and 435 cm-1 (ν2) were observed and are assigned to tetrahedral (A site) and octahedral (B site) groups complex respectively. Morphological study which were determined by scanning electron microscopy (SEM) which shows grains agglomerated with different shapes and sizes. The initial permeability was measured at different frequencies. The fast decrease in initial permeability µi at Tc is a good reason to be a very strong candidate for magnetic switch devices.

Effect of Al3+substitution on the electrical and magnetic properties of Li-base ferrites

Aluminum substituted lithium ferrites with chemical formula Li0.6 (Ni Co)0.2Alx Fe2.2−x O4 (x = 0.0 ,0.15,0.3,0.45,0.6) have been synthesized by sol-gel method and sintered at 900 °C for 5 h. The samples were characterized by XRD, electrical, dielectric and VSM measurements. X-ray diffraction studies confirmed that all the samples exhibit single phase cubic spinel structure with space group Fd3m. The crystallite size, bond lengths, x-ray density and lattice parameters decrease with the increase of Al3+ concentration. Dielectric properties such as dielectric constant (ε′), complex dielectric constant (ε″), tangent loss (tanδ) and ac conductivity (σac) of all the samples were measured and evaluated as a function of frequency at room temperature. The variation of dielectric properties; ε′, ε″, tan and σac versus frequency reveals that the dispersion is due to Maxwell–Wagner type of interfacial polarization in general and the hopping of charge between Fe2+ and Fe3+. The Al-doped nano-crystalline lithium ferrite samples exhibit a very large value of dielectric constant of the order of 104. The room temperature resistivity and activation energy increases with the increase of Al3+ concentration. The temperature dependent resistivity of all samples decreases with increase of temperature indicating the semiconducting behavior. The room temperature DC resistivity increases from 1.65 × 1010 to 2.23 × 1011 ohm-cm. The small value of magnetization may be due to canting superparamagnetic spins at the surface of the samples. The decrease in the magnitude of magnetization value may also be due to the presence of Al3+ paramagnetic ions with spin-down orientation instead of Fe3+ cations with spin-up orientation in the octahedral sites. The squareness ratio (Mr/Ms) is less than 1 which indicates single domain behavior. The increase in coercivity is attributed to lattice defects and decrease is associated with the superparamagnetic behavior.

Effect of incorporation of copper on structural properties of spinel nickel manganites by co-precipitation method

The aim of this research work to synthesis the Ni(1−x)CuxMn2O4 NTC ceramics by co precipitation method sintered at 600 °C. The effect of copper on structural and physical properties of nickel manganite examined through XRD, SEM and FTIR analysis. All the diffraction patterns showed the formation of single phase cubic spinel structure with lattice constant 8.5201 Å to 8.3827 Å and average crystallite size (D) 24 nm to 28 nm due to copper doping. Detailed discussion of dislocation density (ρD), mechanical properties (strain), hopping length (tetrahedral LA and octahedral LB), and texture co-efficient using XRD data are reported. FTIR spectra demonstrating two significant absorption bands in between 400 cm−1 to 600 cm−1 confirms the cubic phase of the samples. Thus structural parameters of copper doped in the nickel manganite are correlated using Williamson-Hall and Size-strain analysis method.

Effect of sintering temperature on structural and magnetic properties of bulk Mg-ferrites

AbstractThe present work focuses on the effect of sintering temperature on structural and magnetic properties of bulk MgFe2O4 ferrites prepared by the solid state reaction method and sintered at 1 200 °C, 1 300 °C and 1 400 °C. Single phase cubic spinel structure was confirmed by X-ray diffraction. The bulk density, grain size and initial permeability increase with sintering temperatures. Decrease of hysteresis loops with low coercivity was observed in B–H loop studies. Saturation magnetization increases with sintering temperature and a higher value of magnetization at 5 K than 300 K was observed. In this communication the change in properties of bulk Mg-ferrite due to sintering temperature is explained in detail.

Structural and Magnetic Properties of CdCoFe2O4 Nanoparticles

We studied the structure, morphology, and magnetic (at room and low temperature) behavior of CdxCo1-xFe2O4 (x = 0.0–0.6) (CCFO) nanoparticles prepared via citrate gel auto combustion technique. The diffraction pattern indicated the formation of single phase cubic spinel structure. The average crystallite size (D) was altered from 37 to 42 nm with ‘x’. The lattice constants were noticed to be increasing from 0.8419 to 0.8496 nm with ‘x’. The unique morphology was observed for all samples. The saturation magnetization (Ms) was decreased from 28.4 to 3.8 emu/g for x = 0.0 to 0.6 Cd-content. The X-ray (dx) and experimental (dE) densities were observed to be increased from 5.222 ± 0.013 to 5.777 ± 0.020 g/c.c, and 5.351 ± 0.020 to 5.619 ± 0.019 g/c.c respectively. Furthermore, we observed that the coercivity was changed from 922 to 2600 Oe as a function of composition. The zero field cooled (ZFC) and field cooled (FC) curves of x = 0.5 content revealed the blocking temperature TB ~ 359 K suggesting the superparamagnetic nature above TB.

Study on the formation of CoCr2O4/SiO2 nanocomposite obtained from Co(II) carboxylate and ammonium dichromate

The aim of the present study was to prepare nanocomposites with different CoCr2O4 content (20%, 50%, and 80% CoCr2O4/SiO2 mass%) starting from Co(II) carboxylate and ammonium dichromate using a modified sol–gel method and to evaluate the final product (nature, size and shape) based on the different precursor amount. Thermal analysis was used in order to reveal the formation and decomposition of Co(II) carboxylate to CoO and (NH4)2Cr2O7 to Cr2O3+x, inside the silica gel pores. The oxide mixture interacts at temperatures of ~ 400 °C when Cr2O3+x turn to α-Cr2O3 which leads together with CoO to the formation of CoCr2O4 inside the SiO2 matrix. XRD and FTIR analyses revealed the formation of the single spinel structure in all synthesized samples. The results show that a higher cobalt chromite content inside the silica matrix leads to higher crystallinity. The particle sizes were in nanometer range, and the size variation was small from a sample to another, independent on the concentration (3.9–12.4 nm).