2x O4 Research Articles

Synthesis, structural, Morphological, optical, and magnetic properties of Li2−2x Ni x Al2x Fe2−2x O4, (x = 0,0.4, and 0.5) nanoparticles

Spinel lithium nickel aluminium ferrite nanoparticles (Li2–2x Ni x Al2x Fe2–2x O4), (x = 0.0, 0.4, and 0.5) were prepared through the low temperature solution combustion method. Urea is employed as a fuel for the burning process. The synthesised samples are subjected to thermal analysis, x-ray diffraction, Fourier transformation infrared, Fourier transformation Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, selected area electron diffraction, ultraviolet-visible light spectroscopy, and vibrating sample magnetometry techniques. The thermal analysis revealed a combustion reaction occurring at around 300 °C. The structural and morphology results confirmed the nanoparticle nature and required material composition. The structural, optical, and magnetic properties significantly change, all of the particle size, band gap, coercivity, remnant magnetisation, and squareness ratio revealed a decreasing trend, while the dislocation density, micro-strain, saturation magnetisation, and the magnetic moment revealed a reverse trend as increment of Al and Ni content. The obtained optical, and magnetic properties confirm that the prepared materials are optically active, and soft ferrite nanoparticles. The ease of preparation method, observed good optical and magnetic properties together with cheap and environmentally benign precursor’s sources make achieved nanoparticles as promising material for nonlinear optics, microwave devices, and memory recording and storage applications.

Evaluation and comparision of dc resistivity of NiZrxCoxFe2−2xO4, Ni0.5Sn0.5CoxMnxFe2−2xO4, Mg1−xCaxNiyFe2−yO4 and Mg1−xNixCoyFe2−yO4 nanocrytalline materials

Four series nanocrystalline ferrites with nominal composition, NiZrxCoxFe2−2xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8) Ni0.5Sn0.5CoxMnxFe2−2xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8), Mg1−xCaxNiyFe2−yO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8; y = 0, 04, 0.8, 1.2, 1.6) and Mg1−xNixCoyFe2−yO4 (x,y = 0.0, 0.2, 0.4, 0.6, 0.8) have been fabricated using the microemulsion synthesis route. The synthesized materials are investigated for dc electrical resistivity measurements. The variation of dc electrical resistivity of these materials has been explainedon the basis of hopping mechanism of both holes and electrons.

Study of ferrite Co1 + x Ti x Fe2–2x O4 (0.2 < x < 0.5) nanoparticles for magnetic hyperthermia

Magnetic nanoparticles (MNPs) of Co1 + x Ti x Fe2–2x O4 (0.2 < x < 0.5) ferrite spinel with an average diameter of ~12 nm in a SiO2 shell are obtained by “wet” chemical synthesis and studied by X-ray diffraction, magnetic, and Mossbauer methods. Based on the data on the MNP released heat as a function of the applied external alternating magnetic field (EAMF) strength and frequency, the particle heating mechanisms are studied. The imaginary part of the magnetic susceptibility χ″ identical to the MNP heat release is analyzed at room temperature in an EAMF of strength 1 Oe and a frequency of 100 Hz. The χ″ maximum temperature decreases with increasing Ti content in CoTi spinel. An increase in the temperature by ~10 K was observed in an EAMF of frequency 10 kHz and a strength of 300 Oe. The temperature increase rate ΔT/dt was measured in the range from 0.001 to 0.008 K/s depending on the EAMF frequency and sample composition. It is found that Co1 + x Ti x Fe2–2x O4 MNPs synthesized at 0.2 < x < 0.5 satisfy the requirements imposed on materials used as heat sources during magnetic hyperthermia. Based on measurements of the magnetic susceptibility in an EAMF and Mossbauer studies, it is shown that CoTi ferrite MNPs with a titanium ion content x = 0.3, i.e., Co1.3Ti0.3Fe1.4O4, are most efficient for magnetic hyperthermia.

Electrochemical studies of LiCr x Fe x Mn2−2x O4 in an aqueous electrolyte

In this paper, LiCr x Fe x Mn2−2x O4 (x = 0, 0.05, 0.1) electrode materials were prepared by sol–gel technique and characterized by X-ray diffraction (XRD) and transmission electron microscopy or high-resolution transmission electron microscopy techniques. XRD results reveal that the Cr–Fe-co-doped LiCr x Fe x Mn2−2x O4 materials are phase-pure spinels. The electrochemical properties of the LiMn2O4, LiCr0.05Fe0.05Mn1.9O4, and LiCr0.1Fe0.1Mn1.8O4 electrodes in 5 M LiNO3 aqueous electrolyte were investigated using cyclic voltammetry, AC impedance, and galvanostatic charge/discharge methods. In the current range of 0.5–2 A g−1, the specific capacity of the LiCr0.05Fe0.05Mn1.9O4 electrode is close to that of the LiMn2O4 electrode, but the specific capacity of the LiCr0.1Fe0.1Mn1.8O4 electrode is obviously lower than that of the LiMn2O4 electrode. When the electrodes are charge/discharge-cycled at the high current rate of 2 A g−1, the LiCr0.05Fe0.05Mn1.9O4 electrode exhibits an initial specific capacity close to that of the LiMn2O4 electrode, but its cycling stability is obviously prior to that of the LiMn2O4 electrode.

Mössbauer study of copper ferrite diluted by Ga3+ and Al3+ ions

Mossbauer spectra of the CuGa x Al2x Fe2 − 3x O4 system (x = 0.1, 0.2, 0.3, 0.4, 0.5) have been studied at a temperature of 295 K. The results obtained are compared with Mossbauer data for the CuGa x Al x Fe2−2x O4 system. It is established that the hyperfine magnetic fields H B (for octahedral sites) and H A (for tetrahedral sites) for ferrites in both systems with ferrimagnetic ordering decrease linearly depending on the total number of nonmagnetic ions in octahedral and tetrahedral sites of the two systems.

Influence of silicon and cobalt substitutions on magnetostriction coefficient of cobalt ferrite

Co1 + x Si x Fe2 − 2x O4 ferrite system has been studied to estimate the influence of Si and Co substitutions together on the magnetic and magnetostrictive properties. The samples were prepared by standard double sintering ceramic technique. X-ray diffraction patterns of the study confirm spinel crystal structures. Hysteresis and magnetostriction measurements were made on all the samples at room temperature. Mossbauer spectra were also made both at 300 K and at 4 K under the applied field of 5 T in the direction of gamma ray. Nominal decreases in Curie temperature and saturation magnetization were observed. The strain derivative, which relates to stress sensitivity, is observed to increase from 1.13 × 10 − 9 to 2.51 × 10 − 9 A − 1 m for x = 0.2 silicon concentration. The variations are explained on the basis of the strength of the exchange interactions between cations, and anisotropy modifications induced by migration of cobalt ions. The results demonstrate the possibility of controlling the magnetic and magnetomechanical properties through Co and Si substitutions.

Influence of magnetic ordering on the structural properties of dilute copper ferrites

The x-ray structural properties of samples in the CuGaxAlxFe2−2x O4 (x = 0−0.7) and CuGaxAl2x Fe2−3x O4 (x = 0−0.5) systems are studied. It is found that magnetic ordering in dilute copper ferrites affects their structural properties. It is concluded that the frustration of magnetic coupling leads to suppression of the cooperative Jahn-Teller effect in dilute copper ferrites with a frustrated magnetic structure.

Magnetic properties of the mixed spinel Co1+x Si x Fe2−2x O4

The structural and magnetic properties of the mixed spinel Co1+x Si x Fe2−2x O4 system for 0·1≤x≤0·6 have been studied by means of X-ray diffraction, magnetization, and Mössbauer spectroscopy measurements. X-ray intensity calculations indicate that Si4+ ions occupy only tetrahedral (A) sites replacing Fe3+ ions, and the added Co2+ ions substitute for (B) site Fe3+ ions. The Mössbauer spectra at 300 K have been fitted with two sextets in the ferrimagnetic state corresponding to Fe3+ at the A and B sites, forx≤0·3. The Mössbauer intensity data shows that Si possesses a preference for the A site of the spinel. The variation of the saturation magnetic moment per formula unit measured at 300 K with the Si content, is explained on the basis of Neel’s collinear spin ordering model forx≤0·3 which is supported by Mössbauer, and X-ray data. The Curie temperature decreases nearly linearly with increase of the Si content, forx=0·1–0·6.

Study of the magnetic properties of ferrites in the CuGaxAlxFe2−2x O4 system having a frustrated magnetic structure

This paper reports a first preparation of samples of the CuGaxAlxFe2−2x O4 system (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7) and a study of temperature dependences of their spontaneous magnetization σ s, coercive force H c, and of the longitudinal, λ∥, and transverse, λ⊥, magnetostriction. Our experimental data have established that compositions with x>0.4 undergo two magnetic phase transitions, namely, from the paramagnetic to cluster spin-glass state at the Curie temperature T C, and another transformation, at T tr<T C, from the cluster spin glass to a frustrated magnetic structure. It was found that the coercive force of ferrites with a frustrated magnetic structure is an order of magnitude lower than that of ferrimagnetically ordered ferrites. The behavior of the magnetostriction of frustrated ferrites was studied. Such ferrites were found to exhibit a considerable positive magnetostriction of the paraprocess λ para. It was shown that the magnetostriction of spin-glass ferrites is lower by nearly an order of magnitude.

Magnetic ordering in Mg1+x Mn x Fe2−2x O4 system

Magnetization measurements of the ferrite system Mg1+x Mn x Fe2−2x O4 were undertaken primarily to study variation of the saturation magnetization with manganese concentration and to gain information about the type of magnetic ordering. The observations indicate the existence of Yafet-Kittel (YK) type of magnetic ordering in this system which is well supported by results of Mössbauer effect measurements. A molecular field analysis of the YK spin ordering using the three-sublattice model is shown to explain the experimental data satisfactorily.

Conduction in Mn substituted Ni-Zn ferrites

The d.c. electrical resistivity ‘ρ’ and thermoelectric power ‘α’ are studied as a function of temperature for Mn substituted ferrites with general formula Zn0·3Ni0·7+x Mn x Fe2−2x O4. At lower Mn concentrations, the increase in d.c. resistivity is attributed to the hindering of Verwey mechanism Fe2+ ⇌ Fe3+ due to stable bonds of Mn3+ + Fe2+ pair. The decrease in resistivity at higher Mn concentrations (i.e. whenx > 0·15) is attributed to the formation of Mn3+ cluster and Ni2+ ⇌ Ni3+. The activation energy values show one to one correspondence with resistivity values. The compositional variation of thermoelectric power showsn-type behaviour for the samples withx < 0·2 whereasp-type behaviour for the samples withx ⩾ 0·2. Thep −n transition is attributed to the formation of Ni3+, Fe2+ + vacancies which act asp-type carriers. The temperature dependences ofα, ρ, and mobility clearly confirm the conduction mechanism to be due to polaron hopping.

Stability of phases in copper ferrite

Abstract Phase stabilities in copper ferrite are studied with substitution of Ti and Ge tetravalent ions. In Ti-substituted samples (Cu1+x Ti x Fe2x O4) the parent tetragonal structure is retained up to x=0.15, and for higher content of Ti it changes to cubic. In the case of Ge-substituted samples (Cu1+x Ge x Fe2–2x O4), the cubic structure is observed for 0.0<x≤0.2, and the tetragonal structure reverts for higher contents of Ge. The origin of the distortion lies in square covalent bond formation of copper ions at the octahedral site. The observed results are explained on the basis of cation distribution and covalent bond formation of copper and germanium ions.

Conduction mechanism in Sn4+ substituted copper ferrite

Thermoelectric power (α) and electrical resistivity (ρ) are reported for the system Cu1+x Sn x Fe2−2x O4 (wherex=0·05, 0·1, 0·15, 0·2 and 0·3) from room temperature to 800 K. The compositions withx=0·05 and 0·2 exhibitn-type conduction while the compositions withx=0·1 and 0·15 showp- ton-type conduction change after 423 K. The conduction at low temperature (i.e. < 400 K) is due to impurities, while at higher temperature (i.e. > 400 K), it is due to polaron. Hopping conduction phenomenon for the present system has been explained on the basis of localized model of electrons. Additional localization may arise due to Sn4+ + Fe2+ stable pairs at B-site and Cu1+ + Fe3+ pair at A-site.