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Structure and magnetic properties of manganese-zinc-ferrites prepared by spray pyrolysis method


Abstract and Figures

A spray pyrolysis of a water solution of iron, manganese and iron nitrates is applied to prepare Zn0.5Mn0.5Fe2O4 single-phase ferrite with a spinel-type structure. The samples are characterized by means of differential scanning calorimetry, scanning and transmission electron microscopy, X-ray diffraction, infrared and Fe-57 Mossbauer spectroscopy. The mass magnetization sigma and the magnetic susceptibility l/chi of the ferrites are measured as a function of temperature over the range of 78-728 K. The obtained sample contains nanoparticles with an average diameter d similar to 7 nm possessing MnxZny-Fe3_O-(x+y)(4) spinel-type structure with a uniform distribution of manganese and zinc atoms over the ferrite lattice. The Curie temperature is determined to be 375 divided by 380 K.
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Edited by Prof. V. Skorokhod
September 14-18, 2009
Warsaw, Poland
Ivanovskaya Maria1, Kotsikau Dzmitry1, Pankov Vladimir1, Fedotova Yulia2
1Research Institute for Physical-Chemical Problems, Minsk, Belarus, e-mail:
2National Centre of Physics of Particles and High Energies, Minsk, Belarus
Abstract Synthesis conditions, structure and magnetic properties of Mn-Zn-ferrites prepared by spray
pyrolysis of solutions of manganese, zinc and iron nitrates have been considered. The applied
technique provides low-temperature (650 °C) obtaining highly dispersed (7-8 nm) powder of
Mn0.5Zn0.5Fe2O4 ferrite with a narrow size distribution. Synthesis of Mn0.5Zn0.5Fe2O4 at low
temperature avoids MnII MnIII oxidation reaction that influences the ferrite properties. IR data
collected from the ferrite samples obtained both in air and in N2 ambient indicate their high structural
and concentration homogeneity. Magnetic measurements confirm single-phase structure of the
Mn0.5Zn0.5Fe2O4 powders and give no evidence of the presence of individual iron oxide phases. Curie
temperature (375-380 K) is consistent with the theoretically calculated value for Mn1-xZnxFe2O4 (x =
0.5) (Tc = 365÷385 K). Parameters of Moessbauer spectra of the ferrites are typical of FeIII state in
oxide solid solutions with a considerable ionicity contribution in Fe-O bonds (δ = 0.33÷0.34 mm/s).
FeII state was not revealed by Moessbauer spectroscopy that indicates the absence of FeIII FeII
reduction accompanying the MnII MnIII oxidation process.
The magnetic properties of Mn–Zn-ferrites are known to depend on their phase
composition and other structural features. The studied ferrites are Mn1–xZnxFe2O4 solid
solutions differing in structural and concentration inhomogeneity. To achieve the best
magnetic characteristics, the preparation of a product consisting of single spinel-type
phase with no traces of iron oxide or other ferrite phases (MnFe2O4, ZnFe2O4) is
required. The oxidation state of zinc, manganese and iron cations, and manner of their
distribution over the spinel crystal lattice also influence the magnetic behavior of the
Mn–Zn-ferrites. According to the Neel theory, maximum magnetization value is
reached when bivalent cations (Zn2+, Mn2+) occupy tetrahedral positions of the spinel
lattice, while trivalent cations (Fe3+) – octahedral ones.
In the technological cycle of the ferrite fabrication, Mn2+ Mn3+ oxidation
reaction may occur at high temperature, which is likely accompanying by reduction of
Fe3+ ions to Fe2+ state and also by redistribution of the metal cations between the
sublattices. Namely, partial swap of the generated Fe2+ and Mn3+ ions between
tetrahedral and octahedral lattice sites is possible. The described processes have an
adverse effect on the magnetic features of the material. Oxidation of Mn2+ ions is known
to proceed most rapidly at 900–1000 °C, while the optimal temperature to produce Mn–
Zn-ferrites lies in the temperature range 1000–1200 C. Specific cooling modes,
including oxygen control in the furnace chamber, are typically applied to avoid Mn2+
oxidation and produce ferrites with the proper functional features. However, the only
reliable way to produce ferrites in a form of powder, preventing Mn2+ oxidation, is to
reduce the synthesis temperature. Instead of conventional ceramic processing
techniques, a number of modifications of the nanotechnology can be used to obtain
nanocrystalline ferrites at comparatively low temperature, in particular, i) thermally
stimulated dehydration of co-precipitated hydroxides of the corresponding metals or
ii) spray pyrolysis of their nitrates [1, 2].
As shown in [3], spray pyrolysis of metal nitrate solutions yields ferrites at
temperature decreased down to 650 °C. An important point is that, this technique
ensures highly homogeneous distribution of the components over the resultant product,
since the formation of its structure proceeds within microscopic droplets of the reacting
In this paper, we present a study of the structural features and magnetic properties
of Mn–Zn-ferrites prepared using low-temperature spray pyrolysis of a mixture of the
metal nitrates.
Experimental procedure
To synthesize Mn–Zn-ferrite by spray pyrolysis, we used water solution of
Zn (II), Mn (II) and Fe (III) nitrates with a concentration corresponding to
0.25 mole/dm3 of Zn0.5Mn0.5Fe2O4. The solution was prepared by mixing the individual
metal nitrate solutions in the required proportion. The ferrite samples were obtained in a
tube furnace through which droplets of the liquid mixture, produced by ultrasonic
atomizer, were entrained by a flow of air or nitrogen. The temperature of the hot face
was 650 °C.
Thermal analysis (DSC, TG, DTG) of the mixed aqueous solution of Zn (II),
Mn (II) and Fe (III) nitrates was carried out on a NETZSCH STA 449 C instrument
using alumina crucible in temperature range 30–1000 °C. The sample weight was
54.280 mg.
IR spectra were collected on a Thermo Nicolet AVATAR FTIR-330 spectrometer
in diffuse reflection mode in the ν range 400–4000 cm–1. A small amount of finely
grinded powders was applied to a polished steel substrate.
X-ray diffraction (XRD) patterns were collected from the powders on a DRON-
2.0 diffractometer with Ni-filtered CoKα radiation (λ = 0.178896 nm) in the 2θ range
20–80°. Evaluation of the results was carried out by a standard procedure using JCPDS
PDF data.
Morphology and grain size of the samples were estimated by scanning electron
microscopy (SEM) on a LEO 1402 instrument, and by transmission electron
microscopy (TEM) on a LEO 903 microscope. In the TEM studies, direct carbon
replicas of the surface were examined. The replicas were formed by the deposition of a
thin layer of carbon onto powder samples in a vacuum evaporator. Then the replicas
were removed by dissolving the ferrite powder in HCl solution. Etching length that
enables to keep some ferrite powder on the carbon films was selected. Then the replicas
were picked up onto TEM grids.
Room temperature 57Fe Mössbauer spectroscopy was applied to reveal local
structure and magnetic state of the ferrite samples. The spectra were recorded using
MSMS2000 spectrometer in transmission geometry using 57Co/Rh source (40 mCi). The
fitting procedure was performed with the use of MOSMOD program assuming the
distribution of hyperfine magnetic fields (Hhf) and electric quadrupole splittings (EQ).
All isomer shifts (δ) were referenced to α-Fe.
Mass magnetization and magnetic susceptibility of the samples were measured as
a function of temperature by Faraday’s method in cooling and heating modes with an
applying magnetic field H = 0.86 T in the range 78–728 K.
Results and Discussion
The results of thermal analysis of aqueous solution of Zn(II), Mn(II) and Fe(III)
nitrates with the metal ratio corresponding to Zn0.5Mn0.5Fe2O4 composition are shown in
Fig. 1.
Fig. 1 DSC, TG and DTG curves recorded from a mixed aqueous solution of Zn(II),
Mn(II) and Fe(III) nitrates with Zn:Mn:Fe = 0.5:0.5:2 molar ratio
As expected, the nitrates of the metals in question melt at 40–80 °C. Note, that in
the beginning of heating, the formation of a colloidal solution may occur owing to the
polycondensation of the nitrate aquacomplexes through bridge OH-groups. As a result,
mixed polymerized precursors, [(Fe2+, Mn2+, Zn2+) (NOx, OH, H2O)], are formed. Their
thermal treatment enables the preparation of highly homogeneous oxide product. It
follows from the thermal analysis results that the removal of water and nitrate ions and
the formation of metal oxide phases proceed simultaneously, and get completed at
200 C. No evidences of possible Mn2+ oxidation are present in the DSC–TG–DTG
curves within temperature range 200–1000 °C. According to the IR spectroscopy results
reported in [4], the removal of NOx anion-radicals occurs most rapidly at 200–300°C
and reaches completion at 500 °C under thermal decomposition of powder mixture of
metal nitrates with the same composition as used in this paper.
In the X-ray diffraction patterns of the samples synthesized both in air and in
nitrogen, the reflections form spinel-type Mn–Zn-Fe2O4 ferrite phase was detected. The
reflections can be attributed to both Mn0.4Zn0.6Fe2O4 (JCPDS no. 74-2400) and
Mn0.6Zn0.4Fe2O4 (JCPDS no. 74-2401) phases, which have close unit-cell parameters.
The presence of other phases was not revealed in the samples by XDR analysis.
Average grain size estimated by the broadening of the XRD reflections lies in the range
6–8 nm.
According to SEM results given in Fig. 2a, the prepared samples consist of
regularly shaped, spherical particles.
Fig. 2 SEM (a) and TEM (b) images of the Mn–Zn-ferrite obtained in nitrogen
The surface morphology of the spheres is typical of amorphous or glassy
materials. The particle diameters range from 150 nm to 1.6 µm with a predominate size
650–800 nm. Spray pyrolysis in nitrogen atmosphere gives narrower distribution in
particle size as compared to the samples synthesized in air. The observed particles are
loose and polycrystalline. They consist of finer particles aggregated into bigger ones
after the formation of the ferrite structure during the spray pyrolysis processing. As
evidence, fine primary particles were distinguished in the TEM images of direct carbon
replicas of the powder ferrite samples (Fig. 2b). The diameter of these particles
corresponds to the average crystallite size determined by XRD.
It is known, that stretching vibrations νFe–O and bending vibrations δFe–ОН in iron
oxides are strongly influenced by the symmetry of oxygen coordination and by force
constant of Fe–O bond. In particular, the νFe–O absorption bands in the IR spectra of
spinel-type γ-Fe2O3 oxide, obtained by heating of γ-FeOOH at 300 °C, are centered at
420, 440, 551, 632 and 691 cm–1 (Fig. 3, spectrum 1).
Fig. 3 IR spectra of γ-Fe2O3 (1) and Mn–Zn-ferrite obtained in nitrogen (2)
and in air (3)
As shown in [5, 6], the formation of zinc or cobalt ferrites by introduction of Zn2+
and Co2+ ions into γ-Fe2O3 are accompanied by the shift of the main νFe–O band towards
greater frequencies. Similar changes we observe for our samples in Fig. 3 when
compare individual γ-Fe2O3 oxide and the Mn–Zn-ferrite samples (420 430 cm–1,
551 559 (571) cm–1). The absence of the band assigned to γ-Fe2O3 phase (632,
691 cm–1) in the spectra 2 and 3 confirms the formation of ferrite structure. Symmetric
shape of the νFe–O bands in the IR spectra of the ferrites testify for homogeneity of the
Mn0.5Zn0.5Fe2O4 spinel structure and uniformity of Zn2+ and Mn2+ distribution over the
IR absorption bands attributed to bending vibrations of OH groups directly
connected to metal cations (δM–ОН) are known to be very sensitive to a degree of the
structural perfection of composite oxides [6]. Therefore, the region of IR spectra around
the mentioned band can be used to evaluate the structural perfection of multicomponent
spinel-type oxides. The characteristic bands of the Mn–Zn-ferrites are 832 cm–1 (δZn–О
Н) and 946 cm–1 (δMn–ОН). The bands around 1030–1122 cm–1 attributed to δFe–ОН are
also shifted against the corresponding γ-Fe2O3 bands thus reflecting the effect of Zn2+
and Mn2+ cations.
It follows from the reported IR results that the synthesized samples have Mn–Zn-
Fe2O4 spinel-type structure with uniform distribution of manganese and zinc over the
ferrite lattice.
Temperature-dependent magnetization σ = f(T), squared magnetization σ2 = f(T)
and magnetic susceptibility 1/χ = f(T) curves for the ferrite sample obtained in nitrogen
atmosphere are shown in Fig. 4.
Fig. 4 Temperature dependences of magnetization, squared magnetization, and magnetic
susceptibility measured from the Mn–Zn-ferrite obtained in nitrogen
The Curie temperature TC was determined to be 375÷380 K. These values are
consistent with the TC range theoretically calculated for Mn0.5Zn0.5Fe2O4 ferrite under
variation of Fe3+ distribution over the crystal lattice (365÷385 К). Individual iron oxide
phases, γ-Fe2O3 (TC = 865 K) and α-Fe2O3 (TN = 965 K), were not revealed in the
synthesized samples from the magnetic measurements. The shape of the σ = f(T) curves
and the σ values, which lie in the range 100÷300 K, are expected for nanosized ferrites
with an equal Mn:Zn ratio.
Room temperature Mössbauer spectra of the ferrite samples synthesized by spray
pyrolysis both in nitrogen and in air flow represent quadrupole doublets indicating
paramagnetic state of iron. Note that paramagnetic state is typical of nanosized Mn–Zn-
ferrites below their Curie point. Similar parameters of the spectra of the ferrites obtained
in nitrogen and in air suggest that Mn2+ Mn3+ and Fe3+ Fe2+ reactions did not take
place under the applied synthesis conditions. Fe2+ state was not revealed by Mössbauer
spectroscopy in the sample prepared in nitrogen atmosphere. Isomer shift values
measured for the samples (δ = 0.33÷0.34 mm/s) are characteristic of Fe3+ ions in oxide
solid solutions, including Mn–Zn-ferrites, and points to a significant ionicity
contribution into Fe3+–O covalent bond [7]. The observed broadening of the Mössbauer
peaks is caused by the combination of poor crystallinity of the ferrite phase and
nanosized scale of the particles.
The measured electric quadrupole splitting values EQ (0.42÷0.53 mm/s) lies
between the values characteristic of individual MnFe2O4 (0.54 mm/s) and ZnFe2O4
(0.32 mm/s) ferrites that confirms the formation of the expected Zn0.5Mn0.5Fe2O4
composition. The quadrupole splitting observed in the Mössbauer spectra is due to the
distorted symmetry of oxygen coordination around Fe3+ ions located in the octahedral
sites. The distortion is a result of filling tetrahedral sites of spinel lattice by Zn2+ and
Mn2+ ions, which have diameters greater than Fe3+. Local distortion of oxygen
coordination can also be evoked by Mn3+ ions occurred in the ferrite structure; however,
this fact did not find confirmation since the decrease of neither TC nor σ values were not
observed for the studied ferrites.
Single-phase Zn0.5Mn0.5Fe2O4 ferrite with spinel-type structure was synthesized
by spray pyrolysis of a water solution of Fe(III), Mn(II) and Fe(III) nitrates at 650 °C.
The ferrite sample consists of primary particles with a size d ~ 7 nm, which are
aggregated into spherical particles with d = 0.15–1.6 µm. The presence of single
nanosized ferrite phase in the sample was confirmed by magnetic measurements.
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... To synthesize spinel ferrites, the authors of [164] proposed an aerosol spray pyrolysis method consisting in the ultrasonic dispersion of liquid media to form an aerosol, which is subsequently subjected to a heat treatment. Aerosol spray pyrolysis provides the synthesis of smaller nanoparticles compared with those formed by spray drying. ...
... In terms of improving the magnetic characteristics, the doping of magnesium ferrite with ions of other metals appears to be more promising. The authors of [164] synthesized spherical Mg 0.5 Zn 0.5 Fe 2 O 4 particles with a size of about 4-12 nm and improved magnetic properties by aerosol spray pyrolysis from an aqueous solution of metal nitrates (Fig. 12). ...
... Scanning electron microscopy and transmission electron microscopy images of Mn-Zn ferrite synthesized in nitrogen[164]. Scanning ...
... Nanosized ferrites were also proven to be good photocatalysts for a broad range of reactions [12]. The coupling of graphene with ferrite nanoparticles enabled the degradation of different pollutants and their recovery after reaction [1,13]. The photocatalytic degradation of organic pollutants, especially dyes used in the textile industry, is considered a promising approach for wastewater treatment [14]. ...
... With increasing the Mn content, the absorption edge shifts to higher wavelength. Fig. 4b shows the Tauc plot used to estimate the optical bandgap of the samples annealed at 1000 • C. The band gap energy value of Mn 01 Zn 09 Fe 2 O 4 (2.09 eV) is in accordance with the previously reported values [13]. The band gap decreases considerably by increasing Mn content, which might be due to the presence of doping states induced in the band gap by additional paths between the conduction band and the valence band [30]. ...
... The calculated rate constants and correlation coefficients corresponding to Figure 6b are listed din The photogenerated electrons in Mn 0.1 Zn 0.9 Fe 2 O 4 with the highest rate of photodegradation, can readily move to the surface and produce anion radicals (O 2− ) from molecular oxygen (Eqs. [12][13][14][15]. The photogenerated holes in the valence band of Mn 0.1 Zn 0.9 Fe 2 O 4 can oxidize RhB dye directly or produce hydroxyl radicals (OH − ) from adsorbed water molecules (Eq. ...
The structure, morphology and photocatalytic features of the Mn-Zn ferrite nanoparticles embedded in SiO2 matrix produced by a modified sol-gel synthesis were investigated. The synthesis consists in the mixing of the metal nitrates, 1,4-butanediol and tetraethylorthosilicate, formation of the SiO2 matrix by gelation, formation of the metallic succinate precursors by heating the gel up to 200 °C and formation of the ferrite system by thermal treatment at higher temperatures. The formation of Mn-, Zn- and Fe-succinate precursors up to 200 °C and their decomposition into ferrites up to 400 °C was confirmed both by thermal analysis and Fourier-transform infrared spectroscopy. The X-ray diffraction provided information on the crystalline phases, crystallite size and lattice constant, while the morphology of the samples was investigated by transmission electron microscopy. The crystallite size increased (30.5-53.4 nm), while the energy band gap of the samples decreased (2.09-1.33 eV) with the increase of the Mn content in the ferrite; thus, the amount of manganese nitrate used in the synthesis could be an easy tailoring approach of the mixed Mn-Zn ferrites. All samples showed sonophotocatalytic activity, being able to degrade Rhodamine B under visible light irradiation, Mn0.3Zn0.7Fe2O4@SiO2 sample having the best sonophotocatalytic performance.
... The spray pyrolysis method consists in converting the reagent mixture into aerosol droplets, solvent evaporation, solute condensation, and drying followed by thermolysis of the particles at high temperature [50]. This method allows the control of the particle formation environment by dividing the solution into droplets [90]. Generally, it is suitable for the synthesis of mixed metal ferrites as it ensures complete stoichiometry retention on the droplet scale and provides a highly homogeneous distribution of the components [90]. ...
... This method allows the control of the particle formation environment by dividing the solution into droplets [90]. Generally, it is suitable for the synthesis of mixed metal ferrites as it ensures complete stoichiometry retention on the droplet scale and provides a highly homogeneous distribution of the components [90]. By controlling the type of thermolysis reaction, the type of precursors, the gaseous carrier, deposition time, and substrate temperature, this method allows the synthesis of a broad range of hollow or porous particles with potential applications in thermal insulation or catalyst support [90,91]. ...
... Generally, it is suitable for the synthesis of mixed metal ferrites as it ensures complete stoichiometry retention on the droplet scale and provides a highly homogeneous distribution of the components [90]. By controlling the type of thermolysis reaction, the type of precursors, the gaseous carrier, deposition time, and substrate temperature, this method allows the synthesis of a broad range of hollow or porous particles with potential applications in thermal insulation or catalyst support [90,91]. ...
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In the last decade, research on the synthesis and characterization of nanosized ferrites has highly increased and a wide range of new applications for these materials have been identified. The ability to tailor the structure, chemical, optical, magnetic, and electrical properties of ferrites by selecting the synthesis parameters further enhanced their widespread use. The paper reviews the synthesis methods and applications of MFe2O4 (M = Co, Cu, Mn, Ni, Zn) nanoparticles, with emphasis on the advantages and disadvantages of each synthesis route and main applications. Along with the conventional methods like sol-gel, thermal decomposition, combustion, co-precipitation, hydrothermal, and solid-state synthesis, several unconventional methods, like sonochemical, microwave assisted combustion, spray pyrolysis, spray drying, laser pyrolysis, microemulsion, reverse micelle, and biosynthesis, are also presented. MFe2O4 (M = Co, Cu, Mn, Ni, Zn) nanosized ferrites present good magnetic (high coercivity, high anisotropy, high Curie temperature, moderate saturation magnetization), electrical (high electrical resistance, low eddy current losses), mechanical (significant mechanical hardness), and chemical (chemical stability, rich redox chemistry) properties that make them suitable for potential applications in the field of magnetic and dielectric materials, photoluminescence, catalysis, photocatalysis, water decontamination, pigments, corrosion protection, sensors, antimicrobial agents, and biomedicine.
... ese properties are useful in a variety of technological advancements and applications, which include photocatalysis for renewable energy generation [3], cancer treatment [4], agents for antibacterial [5], electromagnets [6], gas sensors, biomedicine [7], switching devices [8], drug delivery [9,10], magnetic recording [11], water splitting [12], magnetic resonance imaging [13], multilayer chip inductors [14], supercapacitors [15], and spintronics, among others. Recent significant attention on nanomaterial based magnetic materials such as spinel ferrite nanomaterials can be attributed to their unique properties, which include the ability to adjust their optical, structural, magnetic, and electronic properties through doping as well as vacancy creation [16][17][18][19]. By altering the size, shape, manufacturing technique, dopant ions, and their concentration, various physical properties of a system containing nanoparticles can be changed [20][21][22]. ...
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... The characterizations of ZnCu ferrites are studied with an X-ray diffractometer, scanning electron microscopy [74][75][76]. The magnetic properties of the ferrites are studied by vibrating sample magnetometer (VSM), magnetization hysteresis (M − H) loops [77], and electron spin resonance (ESR) hysteresis loop measurements. ...
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... The intensity of the vibration band at 562-578 cm −1 increases with the increase of calcination temperature, most probably due to the increase of the ferrite's crystallinity, as ferrites acts as continuously bonded crystals with atoms linked to all nearest neighbors by equivalent ionic, covalent or van der Waals forces [21,23,24]. The increase of calcination temperature determines a small shift of the vibration band due to the changes in the ion's distribution between A and B sites [23][24][25][26]. The specific bands of the SiO2 matrix were identified in the FT-IR spectra of NPs with δ = 0-75%: 1078-1106 cm −1 with a shoulder around 1200 cm −1 assigned to vibration of Si-O-Si chains, 792-809 cm −1 assigned to the vibrations of SiO4 tetrahedron and 457-479 cm −1 assigned to the Si-O bond vibration that is overlapping the band of Fe-O vibration [13,19]. ...
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... Numerous other methods frequently employed for the synthesis of SFs have been reported in the literature, including flame spray pyrolysis [104], Laser ablation [105], microwave-assisted method [106], electrospinning [107], and mechanical milling method [108]. ...
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Ceramic processing can be defined as the set of operations by which, from one or more starting materials, parts with desired shape and structure are obtained. The advent of materials science and the development of new technologies allowed ceramic products to be inserted in the most diverse sectors of the industry. This chapter covers the fundamental concepts involved in the various stages of ferrite processing, from the dispersion of particles to the consolidation of a bulk or thin film.
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The magnetic properties of Mg 1-x Zn x Fe 2 O 4 (where x = 0.3,0.4,0.5,0.6) ferrites have been studied. Magnesium Zinc Ferrites was synthesized by oxalate co-precipitation method at different synthesis temperature and characterized by X-ray diffraction and far IR absorption techniques, scanning Electron microscopy .The lattice parameter were computed . The X-ray diffraction studies reveal the formations of single phase cubic spinel structure.IR absorption bands are observed around 600 cm -1 and 400 cm -1 on the tetrahedral and octahedral sites respectively. Magnetization parameters such as saturation magnetization, and magnetic moment were calculated and the results are discussed with the help of the existing theories. Saturation magnetization was found to be in the range 2 emu/gm to 8.28 emu/gm when the samples were synthesized below 100ºC. The variation of A.C. susceptibility with temperature shows the existence of super paramagnetic nature. The Curie temperature was determined from the measurement of the susceptibility verses temperature. The SEM micrographs shows the uniform distribution of the particles, the average size was estimated to be 0. 350 µm.
The structural properties and gas-sensitivty of sol-gel-synthesized ceramic and film metaloxide sensors were investigated. Oxide systems obtained by thermal treatment of stabilized colloidal dispersions of metal hydroxides were characterized by high dispersity, defectivity of crystal lattice, and formation of nonequilibrium oxide phases. Electron spin resonance spectra observed the formation of significant amounts of single charged oxygen vacancies in slightly different coordination neighborhood found in sol-gel obtained SnO2.
Doped BaFe11.92(LaNd)(0.04)O-19/titanium dioxide composites have been prepared by the gel-precursor self-propagating combustion process. The characterization of the composites are performed by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Differential thermal analysis-thermo gravimetry (DTA-TG), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and network analyzer. Both XRD and FT-IR indicate that the doped BaFe11.92(LaNd)(0.04)O-19/titanium dioxide composites are successfully synthesized and there are some interactions between BaFe11.92(-LaNd)(0.04)O-19 and titanium dioxide. DTA-TG analysis of BaFe11.92(LaNd)(0.04)O-19/titanium dioxide composites shows that the composite gel decomposition process mainly includes two stages: the first stage is the crystallized water and the residual moisture evaporation: the second stage is the nitrate and citric acid decomposition reaction. SEM demonstrates that the doped BaFe11.92(LaNd)(0.04)O-19/titanium dioxide solid solution has formed. The magnetic parameters indicate that the electromagnetic properties of the composites could be well adjusted by the mass ratio of BaFe11.92(LaNd)(0.04)O-19 and titanium dioxide. When the mass ratio of BaFe11.92(LaNd)(0.04)O-19 and titanium dioxide is 4:5, the composites have the best magnetic loss. The composites with the mass ratio 6:5 of BaFe11.92(-LaNd)(0.04)O-19 and titanium dioxide. BaFe11.92(LaNd)(0.04)O-19 and titanium dioxide possess good dielectric loss. The introduction of titanium dioxide enhances the dielectric loss and widens the frequency bands. The composites will be promising microwave absorption materials with wide frequency band.
A novel graphene-carbon nanotube (graphene-CNT)/CoFe2O4/polyaniline composite with reticular branch structures had been fabricated by in situ chemical polymerization method. The textured structures of the as-prepared composites were characterized by the fourier transform infrared (FTIR) and Xray diffraction (XRD). The morphology was analyzed by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic properties were tested by vibrating sample magnetometer and four-probe conductivity tester. The results showed that the graphene-CNT/CoFe2O4/polyaniline composite had the unique reticular branch structures. When the mass ratio of the graphene-CNT/CoFe2O4 to aniline was 1:3, the magnetic saturation value of the composite achieved 39.6 emu g(-1), and the conductivity reached 1.957 S cm(-1). Based on the experimental results, a probable formation mechanism for the unique reticular branch structures was proposed.
A facile chemical method through hydrothermal synthesis coupled with in situ polymerization to prepare the Mn0.6Zn0.4Fe2O4-carbon nanotubes (CNTs)/polyaniline (PANI) nanocomposites has been reported in this paper. The structure of samples has been characterized by the Fourier transform infrared and X-ray diffraction. The shape and size of samples have been observed by the scanning electron microscopy and transmission electron microscopy. The conductive properties of the Mn0.6Zn0.4Fe2O4-CNTs/PANI nanocomposites have been tested by a four-probe conductivity tester at room temperature. And the magnetic properties are measured by a vibrating sample magnetometer. When the mass ratio of the Mn0.6Zn0.4Fe2O4-CNTs to aniline (m(Mn0.6Zn0.4Fe2O4-CNTs)/m(An)) is 0.15, the Ms, Mr and Hc achieves 15.44 emu/g, 5.06 emu/g and 308.68 Oe, respectively. At the same time the probable formation mechanism of nanocomposites is also investigated based on the experimental results.
The chitosan-decorated ferrite-filled multi-walled carbon nanotube (MWCNT)/polythiophene composites were synthesized through in situ chemical polymerization of thiophene in the presence of the chitosan-decorated ferrite-filled MWCNTs. The structure of the samples was characterized by Fourier transform infrared spectroscopy, X-ray diffraction. The shape and size were observed by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The properties of the samples were tested with the vibrating sample magnetometer and the four-probe conductivity tester. The results showed that chitosan has been decorated onto the surface of MWCNTs. And the MWCNTs have been filled with a large number of ferrite crystals. And the chitosan-decorated ferrite-filled MWCNTs have also been coated with polythiophene. The magnetic saturation value of the chitosan-decorated ferrite-filled MWCNTs/polythiophene composites has achieved 0.18 emu/g, and the conductivity is 1.613 S/cm. Finally, based on the experimental results, the probable formation mechanism of this composite has been investigated.
Nano-crystalline nickel–zinc ferrites of different compositions; Ni1−xZnxFe2O4 (x=0.0–1.0) were prepared by a precursor method involving egg-white and metal nitrates. An appropriate mechanism for the egg-white-metal complexation was suggested. Differential thermal analysis-thermogravimetry, X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer and AC-magnetic susceptibility measurements were carried out to investigate chemical, structural and magnetic aspects of Ni–Zn ferrites. XRD confirmed the formation of spinel cubic structure. The average crystallite size was calculated using line broadening in XRD patterns. Structural parameters like lattice constant, X-ray density, bond lengths and inter-cationic distance were determined from XRD data. TEM showed agglomerated particles with average size agreed well with that estimated using XRD. FT-IR spectra confirm the formation of spinel structure and further lends support to the proposed cation distribution. Zn-content was found to have a significant influence on the magnetic properties of the system. The changes in the magnetic properties can be attributed to the influence of the cationic stoichiometry and their occupancy in the specific sites.
The poly(3-octyl-thiophene)/BaFe11.92(LaNd)0.04O19-titanium dioxide/multiwalled carbon nanotubes (P(3OT)/BF–TD/MCNTs) nanocomposites were synthesized through in situ chemical polymerization of 3-octyl-thiophene in the presence of the BF–TD nanocomposites and MCNTs. Nanocomposites were characterized by thermogravimetry (TG), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM). TG, FT-IR and XRD images indicated the formation of P(3OT)/BF–TD/MCNTs nanocomposites. SEM and TEM observations showed the particles size of the BF–TD nanocomposites was less than 50 nm and lots of MCNTs were absorbed by BF–TD nanocomposites. Under applied magnetic field, the nanocomposites exhibited the ferromagnetic behavior. The saturation magnetization, remanent magnetization and coercivity of nanocomposites varied with the content of Ba(LaNd)0.09Fe11.82O19 particles. A scheme for the formation of the nanocomposites was proposed. When the BF and TD mass ratio was 6:5, P(3OT)/BF–TD/MCNTs nanocomposites possessed the best magnetic parameter.