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In this study, the structural, morphological, and magnetic properties of hydrothermally synthesized Co0.5Ni0.5BixFe2-xO4 (x=0.00–0.10) nanosized spinel ferrites, (CoNiBiFO (x=0.00–0.10) NSFs), were investigated. The formation of CoNiBiFO NSFs phase was confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the morphology of the NSFs. Magnetization revealed that undoped Co0.5Ni0.5Fe2O4 and Co0.5Ni0.5BixFe2-xO4 NSFs (except with x = 0.04) exhibit ferrimagnetic magnetism at 300 K. Only the hysteresis loops recorded from Co0.5Ni0.5Bi0.04Fe1.96O4 NSFs have superparamagnetic characteristics. Mixed Co0.5Ni0.5Fe2O4 NSFs have maximum remnant magnetization (Mr) of 23.5 emu/g, maximum saturation magnetization (MS) of 63.38 emu/g, and maximum magneton number (nB) 2.66 μB. However, Co0.5Ni0.5Bi0.04Fe1.96O4 NSFs have minimum MS of 28.25 emu/g and minimum nB as 1.22 μB among Bi3+ doped and undoped samples. The coercivity (HC) of undoped Co0.5Ni0.5Fe2O4 NSFs is 656 Oe. However, the Bi3+ ion-doped samples have a wide range of HC values between 101 Oe and 1038 Oe. The squareness ratios are in the range of 0.092–0.418 and multi-domain structure is assigned for all types of samples. The measured positive exchange bias (HE) magnitudes are 268 Oe and 290 Oe, respectively. Hysteresis loops recorded at 10 K proved that the products are ferrimagnetic. These coercivities showed that all the samples are magnetically harder at low temperatures. Positive HE values of 165 Oe and 297 Oe were measured from the nanoparticles (NPs) with x = 0.08 and x = 0.10 at 10 K. The SQR of the Co0.5Ni0.5Bi0.04Fe1.96O4 sample at 10 K is almost equal to the critical value of 0.5, and a single domain structure with uniaxial symmetry can be attributed for this sample. The other samples have SQRs in the range of 0.632–0.782 and multi-domain wall structure is assigned for them at 10 K.

Here in the present investigation, constituent phases of (1 − x)Mn0.7Zn0.3Fe2O4(MZFO) + (x)BaTiO3(BTO) (where x = 0.0, 0.25, 0.50, 0.75 and 1.0) composites have been synthesized by sol–gel auto-ignition route and the composite structure by ceramic route. The XRD analysis ensures that the composite structure consists of both cubic spinel piezomagnetic and perovskite piezoelectric phases. The average crystallite size estimated from Scherrer equation increases from 15.36 to 21.94 nm. The strain induced in individual phases has been investigated by W–H analysis and it is observed that the MZFO phase shows comprehensive type strain while BTO phase shows tensile type strain. Scanning electron micrographs confirm the microstructure of the sample with grain size ranges from 36.006 to 54 nm. Energy dispersive X-ray spectra and elemental color mappings of typical samples (x = 0.0 and 0.75) clearly indicates the phase purity and stoichiometric proportion of the composites. Fourier transform infrared spectra showed five major absorption bands related to stretching vibrations of different kinds of metal ions and oxygen ions. Increasing percentage of BTO phase in the composite reduces the saturation magnetization, remnant magnetization and coercivity. Real and imaginary parts of permittivity show maximum values at lower frequency region and decrease with increase in applied frequency. For the composition (0.25)MZFO–(0.75)BTO, composite shows maximum value of magnetoelectric coupling coefficient (αME = 20.45 mVcm−1 Oe−1). The improved magnetoelectric properties make MZFO–BTO composite applicable for electronic devices.

The nanocrystalline samarium substituted Co-Zn ferrites with chemical formula Co0.7Zn0.3SmyFe2–yO4 (where y = 0, 0.01, 0.02, 0.03, 0.04) were synthesized by sol-gel autocombustion route. The analysis of X-ray diffractograms (XRD) reveals the formation of cubic spinel structure. The planes indexed from XRD analyses were confirmed in the selected area electron diffraction (SAED) image of the sample. Nanocrystalline nature of the particles in the ferrite samples was confirmed by TEM. The morphology was analyzed by scanning electron microscopy (SEM). Magnetic measurements show an increase in the magnetization for x ≤ 0.03. The decrease in magnetization due to spin canting is observed for x = 0.04. The coercivity depends on Sm3+ doping concentration, grain size and saturation magnetization. The complex permeability of the ferrites was analyzed as the function of frequency and Sm3+ composition (y). The real part of complex permeability varies linearly with the grain size.

This study explored the microstructural and magnetic features of NiFe2−xDyxO4 (x ≤ 0.10) NPs (nanoparticles) that were synthesized by sol–gel auto-combustion method. The single phase of spinel ferrite has been verified for all samples without any impurity. The cubic morphology of the products was also showed by SEM. Room temperature (300 K) and 10 K magnetization curves were recorded applying a dc magnetic field up to ±50 kOe and it was observed that magnetic features of NiFe2O4 NPs significantly changed by the substitution of Dy3+ ion. Magnetization measurements showed low order of 300 and 10 K magnetic parameters (such as Keff, coercivity and anisotropy field values), revealing soft ferrimagnetic behaviors of all pristine and doped NiDyxFe2−xO4 (0.00 ≤ x ≤ 0.10) NPs at both 300 and 10 K. Pristine NiFe2O4 has maximum magnetic moment and saturation magnetization values among all samples. Dy3+ substitution showed a slight decrement in magnetization values compared with pristine sample. A slight increase in coercivity was noticed with Dy3+ substitution. Squareness ratios (SQRs) have a range between 0.144 and 0.324. These values are smaller than the theoretical limit of 0.50, implying the multi-domain nature for NPs. Blocking temperature (TB) was calculated as 28 K for NiFe2O4 NPs.

This paper emphasizes the structure, morphology, optical, and magnetic properties of sonochemically prepared terbium-substituted cobalt ferrite nanoparticles, CoTbxFe2-xO4 (0.00 ? x ? 0.10). The formation of cubic spinel nanosized ferrite structure was confirmed by X-ray diffraction (XRD), Field-emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared (FT-IR) spectroscopy. The crystallites sizes were found in the range of 11–14 nm. Ultraviolet–visible percentage diffuse reflectance investigations were performed on pristine and Tb3+-doped cobalt spinel ferrite CoFe2O4 nanoparticles. The direct energy band gap (Eg) values were determined by applying the Kubelka–Munk theory and Tauc plots were found to be in a narrow band range of 1.37–1.44 eV. Analyses of magnetization versus the magnetic field (M(H)) were performed. The magnetic parameters, including the saturation magnetization (Ms), squareness ratio (SQR = Mr/Ms), magnetic moment (nB), remanence (Mr), and coercivity (Hc) were evaluated. The M(H) curves exhibited a soft ferrimagnetic nature. It was demonstrated that the Tb3+ substitutions strongly influenced the magnetization data. Indeed, the Ms, Mr, Hc, and nB values decreased with increasing Tb3+ substitution. © 2019 Elsevier Ltd and Techna Group S.r.l. Deanship of Scientific Research, King Saud University: 2018-209-IRMC, 2017-576-IRMC This study was supported by the Deanship of Scientific Research (project applications 2017-576-IRMC and 2018-209-IRMC ) of Imam Abdulrahman Bin Faisal University (Saudi Arabia).

Co-Tm nano-spinel ferrite with chemical formula CoTmxFe2−xO4 (0.0 ≤ x ≤ 0.08) NPs were prepared via sonochemical approach. X-ray powder diffraction patterns, microscopic images (SEM and TEM) and infrared spectra proved the formation of Co spinel ferrite. The effect of Tm3+ substituted on spinal structure was evaluated by lattice parameters, tetrahedral and octahedral bond length and cationic distribution. The band gap energy (Eg) of samples were estimated by performing UV–Vis percent diffuse reflectance (% DR) and applying the Kubelka-Munk theory. Eg values are in an interval between 1.33 eV and 1.64 eV. The analyses of magnetization were performed at room (300 K; RT) and low (10 K) temperatures. Different magnetic parameters including coercivity Hc, saturation magnetization Ms, remanence Mr, squareness ratio (SQR = Mr/Ms) and magnetic moment n B were deduced and discussed. The results showed superparamagnetic (SPM) nature at RT for x = 0.00 and 0.02 samples. However, the other products exhibit ferromagnetic (FM) nature. At 10 K, all synthesized NPs display FM behavior. An amazing increase in the magnitudes of Ms, Mr and Hc was observed at 10 K in comparison to RT, which is principally due to the reduced thermal fluctuations of magnetic moments at lower temperatures. The Tm3+ substitution affects considerably the magnetizations data. An enhancement in the Ms, Mr, and n B was detected on increasing the Tm3+ concentration. The SQR values at RT are found to be smaller than 0.5 postulating a single domain nature with uniaxial anisotropy for all produced ferrites. However, SQRs are in the range 0.66–0.76 at 10 K, suggesting the multi magnetic domain at low temperature, except the x = 0.02 product where the SQR = 0.47 indicating the single magnetic domain. The obtained magnetic results were investigated deeply with relation to structural and microstructural properties.

Multiferroic composites of Zn-Cr substituted cobalt ferrite (Co0.75Zn0.25Cr0.2Fe1.8O4) (CZCFO) nanoparticles and lead-free piezoelectric sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) having composition (1 − x) Na0.5Bi0.5TiO3 + (x)Co0.75Zn0.25Cr0.2Fe1.8O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0) were investigated in this study. Ferromagnetic-CZCFO and ferroelectric-NBT phases were synthesized via sol-gel auto combustion route and solid-state reaction methods respectively. The structural properties of composite materials were studied using X-ray diffraction (XRD) technique. Intense and sharp peaks observed in XRD patterns confirm that both the phases are well crystalline in nature. Two separate phases of CZCFO and NBT are present in composite material without any impurity or chemical reaction among them. The morphology of prepared samples was studied via scanning electron microscopy confirming that composite materials are well-densified and homogenous grain size distribution. The magnetic hysteresis loops of multiferroic composite were investigated by using vibrating sample magnetometer at room temperature. The lead free multiferroic composite exhibiting a large converse magneto-electric (ME) effect at room temperature. The maximum value of ME coefficient (αME = 7.92 kV/cm) is obtained at x = 0.50. Furthermore, electrical properties of nanocomposite material were studied by P-E hysteresis loop and dielectric measurements at room temperature.

ACS omega 6(34), 22429-22438 (2021). doi:10.1021/acsomega.1c03416, Published by ACS Publications, Washington, DC

Tm-Tb co-substituted Co-Ni nanospinel ferrites (NSFs) as (Co0.5Ni0.5) [TmxTbxFe2&minus, 2x]O4 (x = 0.00&ndash, 0.05) NSFs were attained via the ultrasound irradiation technique. The phase identification and morphologies of the NSFs were explored using X-rays diffraction (XRD), selected area electron diffraction (SAED), and transmission and scanning electronic microscopes (TEM and SEM). The magnetization measurements against the applied magnetic field (M-H) were made at 300 and 10 K with a vibrating sample magnetometer (VSM). The various prepared nanoparticles revealed a ferrimagnetic character at both 300 and 10 K. The saturation magnetization (Ms), the remanence (Mr), and magneton number () were found to decrease upon the Tb-Tm substitution effect. On the other hand, the coercivity (Hc) was found to diminish with increasing x up to 0.03 and then begins to increase with further rising Tb-Tm content. The Hc values are in the range of 346.7&ndash, 441.7 Oe at 300 K to 4044.4&ndash, 5378.7 Oe at 10 K. The variations in magnetic parameters were described based on redistribution of cations, crystallites and/or grains size, canting effects, surface spins effects, super-exchange interaction strength, etc. The observed magnetic results indicated that the synthesized (Co0.5Ni0.5)[TmxTbxFe2&minus, x]O4 NSFs could be considered as promising candidates to be used for room temperature magnetic applications and magnetic recording media.

Arabian journal of chemistry 13(10), 7403-7417 (2020). doi:10.1016/j.arabjc.2020.08.017, Published by Saudi Chemical Soc., Riyadh

Journal of materials research and technology : jmr&t 9(5), 11278-11290 (2020). doi:10.1016/j.jmrt.2020.08.027, Published by Elsevier, Rio de Janeiro

Dy3+ and Y3+ ions co-doped Zn0.5Mn0.5Fe2O4 (ZMDyYFe) (x = 0.00–0.05) nanospinel ferrite nanoparticles (SFNPs) have been synthesized through an ultrasonication approach. The rare earth co-doping with Dy3+ and Y3+ ions was applied to tune the structural and magnetic properties of the ZnMn spinel ferrites. The influence of the co-doped of both Dy3+ and Y3+ ions on the structural, optical, and magnetic characteristics of Zn0.5Mn0.5Fe2O4 SFNPs was analyzed in detail by X-ray diffractometry (XRD), scanning electron microscopy (SEM), high- resolution tunneling electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), and elemental mappings. XRD results revealed the formation of the spinel phases and the structural changes which were accompanied the Dy3+ and Y3+ ions co-doping. The cubic spinel phase of all samples has been confirmed by the application of Rietveld refinement. As the value of ``x`` increased up to x = 0.04, the lattice constant was found to increase from 8.401 to 8.408 A and the size of the crystallites was calculated to be in the range 7.26 nm-11.10 nm. HR-SEM and HR-TEM micrographs also presented the cubic morphology of the products. Diffuse reflectance spectroscopy (DRS) measurements were done on pure and Dy3+ and Y3+ co-doped Mn0.5Zn0.5Fe2O4 SFNPs. Direct band gaps (Eg) were extracted from Tauc plots. Eg values existed in a narrow range between 1.64 eV and 1.74 eV. Magnetic investigations exhibited the superparamagnetic behavior at RT (room temperature) and ferrimagnetic behavior at 10 K for synthesized samples. At RT analyzes, undoped Mn0.5Zn0.5Fe2O4 SFNPs had the maximum saturation magnetization (MS) of 34.84 emu/g and magneton number (nB) of 1.47 μB. An inverse proportion with the increasing ion ratio were observed among those parameters. The 10 K magnetization data revealed that co-doped Mn0.5Zn0.5Dy0.02Y0.02Fe1.96O4 SFNPs had magnetic parameters of MS,max= 67.39 emu/g, nB,max = 2.88 μB and HC,max = 574 Oe (HC: coercivity and max: maximum). Among the rest of the co-doped samples, MS and nB data had a similar negative trend with respect to the increasing ion ratio including the remnant magnetizations (Mr). The rest of the HC values were found to be between 275 Oe and 361 Oe. Squareness ratios (SQRs= Mr/MS) had a range of 0.181- 0.321 and confirmed the multi-domain wall structure for all SFNPs at 10 K. The maximum value of effective crystal anisotropy constant (Keff) 6.04 × 104 Erg/g belongs to Mn0.5Zn0.5Dy0.02Y0.02Fe1.96O4 SFNPs, and others have the same order of 104 Erg/g for Keff constants. Although this sample has the largest internal anisotropy field (Ha) of 1794 Oe, it can also be classified as a soft magnetic material like other nanoparticle samples. The Dy3+ and Y3+ ions co-doped ZMDyYFe (x = 0.00–0.05) SFNPs, with varying structural and magnetic properties, can have potential applications in various areas such as magnetic switching, security, magnetic core, microwave absorption applications, nanofabrication and nanodevices.

( x )BaTiO 3 –(1− x )Co 0.7 Fe 2.3 O 4 (BTO-CFO) magnetoelectric nanocomposite ceramic with x = 0.0, 0.25, 0.50, 0.75, 1.00 were successfully designed and fabricated by sol-gel route. The structural, micro structural, dielectric, ferromagnetic, ferroelectric and magnetoelectric properties of these composites were investigated. The coexistence of tetragonal phase and cubic spinel phase, without any secondary phase in composites is confirmed by the X-ray diffraction measurement. The field emission scanning electron micrograph show well distributed ferrite and ferromagnetic phases in the composites. The energy dispersive X-ray results revealed the purity and stoichiometry of BTO-CFO nanocomposites. The dielectric constant and loss factor of the composites were studied as a function of frequency. The composite sample with x = 0.50, results in higher value of dielectric constant whereas CFO possess lowest value of dielectric constant. The magnetization hysteresis (M−H) loop of the composites show ferromagnetic behavior with saturation magnetization values, Ms varies from 15 to 67.68 emu/g and coercive field Hc from 1538 to 1862 Oe. All the composites exhibit typical ferroelectric hysteresis loops indicating the presence of spontaneous polarization. The magnetoelectric voltage coefficient increases linearly with increases in applied d.c. magnetic bias field up to 8 KOe. The maximum value of magnetoelectric voltage coefficient, α ME = 7.7 mV/cm Oe for BTO-CFO composite having 25% ferrite and 75% ferroelectric content. The high ME voltage coefficient of BTO-CFO composite may be suitable for storage device application.

In the present investigation we have studied the role of varying pH and sintering temperature on the properties of copper ferrite nanoparticles synthesized from metal nitrate solutions by sol–gel auto-combustion technique. The CuFe2O4 samples were synthesized with varying pH values (without maintaining pH, pH 4 and 8). The careful analysis of X-ray diffraction (XRD) result showed that the pH provides boost to develop copper ferrite nanoparticles. The samples without maintaining pH suggested the presence of three different phases. The samples with pH values 4 and 8 showed the tetragonal structure. Crystal structure phase transformation of copper ferrite (pH 8) nanoparticles was studied under different sintering conditions. The prepared samples were characterized by XRD, field emission scanning electron microscopy, FTIR and magnetization. These copper ferrite nanoparticles sintered at different temperatures show combinations of cubic and tetragonal phases. The thermal behavior of as-prepared samples was confirmed by thermo gravimetric/differential thermal analyzer analysis. The morphology of materials was understood by SEM technique. The room temperature magnetic measurement proves strong redistribution of Cu2+ ions. Sintering temperature alerts the saturation magnetization (Ms) to a large extent from 9.26 to 25.15 emu/g.

Ce and Dy substituted Cobalt ferrites with the chemical composition CoCe x Dy x Fe 2-2 x O 4 ( x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were synthesized through the chemical route, citrate-gel auto-combustion method. The structural characterization was carried out with the help of XRD Rieveld analysis, SEM and EDAX analysis. Formation of spinel cubic structure of the ferrites was confirmed by XRD analysis. SEM and EDAX results show that the particles are homogeneous with slight agglomeration without any impurity pickup. The effect of RE ion doping (Ce and Dy) on the dielectric, magnetic and impedance studies was systematically investigated by LCR meter, Vibrating Sample Magnetometer and Impedance analyzer respectively at room temperature in the frequency range of 10 Hz–10 MHz. Various dielectric parameters viz., dielectric constant, dielectric loss and ac conductivity were measured. The dielectric constant of all the ferrite compositions shows normal dielectric dispersion of ferrites with frequency. Impedance analysis confirms that the conduction in present ferrites is majorly due to the grain boundary mechanism. Ferrite sample with x = 0.03 show high dielectric constant, low dielectric loss and hence can be utilized in high frequency electromagnetic devices. Magnetization measurements indicate that with increase in Ce and Dy content in cobalt ferrites, the magnetization values decreased and coercivity has increased.

Rare earth (RE) ions are known to improve the magnetic interactions in spinel ferrites if they are accommodated in the lattice, whereas the formation of a secondary phase leads to the degradation of the magnetic properties of materials. Therefore, it is necessary to solubilize the RE ions in a spinel lattice to get the most benefit. In this context, this work describes the synthesis of Co–Zn ferrite nanoparticles and the Gd3+ doping effect on the tuning of their magnetic properties. The modified sol–gel synthesis approach offered a facile way to synthesize ferrite nanoparticles using water as the solvent. X-ray diffraction with Rietveld refinement confirmed that both pure Co–Zn ferrite and Gd3+ substituted Co–Zn ferrite maintained single-phase cubic spinel structures. Energy dispersive spectroscopy was used to determine the elemental compositions of the nanoparticles. Field and temperature dependent magnetic characteristics were measured by employing a vibration sample magnetometer in field cooled (FC)/zero field cooled (ZFC) modes. Magnetic interactions were also determined by Mossbauer spectroscopy. The saturation magnetization and coercivity of Co–Zn ferrite were improved with the Gd3+ substitution due to the Gd3+ (4f7)–Fe3+ (3d5) interactions. The increase in magnetization and coercivity makes these Gd3+ substituted materials applicable for use in magnetic recording media and permanent magnets.

Facile hydrothermal and sonochemistry approaches were employed to synthesize the spinel ferrite NPs Mn 0.5 Zn 0.5 Eu x Sm x Fe 2−2x O4 ( x = 0 .0–0.5), viz. hydrothermal (H-MZESF NPs) and ultrasonic (U-MZESF NPs), respectively. The products were analyzed and compared based on structure, morphology, magnetic and optical properties. The single phase and mixed spinel structures were evidenced by XRD analysis. The crystallite size of the H-MZESF and U-MZESF NPs are within the ranges 8.0–12.5 and 4.5–11.5 nm, respectively. HR-TEM, TEM and SEM analyses proved the cubic morphologies of all the products. DR% measurements indicated that an estimation of the direct energy band gap ( E g ) of all the samples was possible from Tauc plots. The E g values of the H-MZESF and U-MZESF NPs were 1.64 and 1.1 eV, respectively. Co-doping causes significant changes, particularly in the band gap of U-MZESF NPs. Magnetic field and temperature dependent VSM magnetization investigations revealed the superparamagnetic nature at RT and ferrimagnetic nature with a multi domain structure at low temperatures. The magnetization data obtained at 10 K and calculated magneton numbers are (2–2.4) times larger with respect to the data obtained at 300 K. Measured coercivities ( H C ) are in the ranges 210–690 and 318–1182 Oe for the H-MZESF and U-MZESF NPs, respectively. The calculated effective magnetocrystalline constants ( K eff ) are of the order of 104 Erg/g for both types of samples.

In this study, bimetallic (Cu-Mn) substituted M-type Ba 1-2x Mn x Cu x Fe 12 O 19 (0.0 ? x ? 0.1) hexaferrites were fabricated via sol-gel auto-combustion route. The effect of bimetallic substitution on structure, morphology and magnetism of BaFe 12 O 19 was studied. Scanning Electron Microscopy confirm images reveal the nanosize of the prepared products with flake morphology. X-ray powder diffraction analysis confirmed their complete conversion to BaFe 12 O 19 hexagonal crystal phase. The results from the magnetic investigations conducted by Vibrating Sample Magnetometer (VSM) and 57 Fe Mössbauer suggested that the saturation magnetization (M s ) and the coercive field of Ba 1-2x Mn x Cu x Fe 12 O 19 hexaferrites decrease as the concentration of Cu and Mn increases. The cation distribution calculation showed that the occupancy of Fe 3+ ions is increased at 12k and 2b sites with the increase in Cu and Mn substitution. © 2017 Elsevier Ltd and Techna Group S.r.l.

A series of CoAl x Fe 2−x O 4 (0 ≤ x ≤ 1.0) was synthesized by sol-gel auto combustion method using nitrates of respective elements and by keeping 1:3 ratio of metal nitrate to citrate. The resultant powders were investigated by various techniques. Fourier transform infrared spectroscopy (FT-IR) is employed to determine the local symmetry in crystalline solids and to shed light on the ordering phenomenon. The XRD revealed that the powders obtained are single phase with inverse spinel structure. Evaluation of TEM confirms fine particle nature of the particles. SEM analysis and EDAX indicate that the samples were homogeneous and had the expected Fe-Co-Al ratios. As aluminium content increases, the measured magnetic hysteresis curves become broader and the saturation magnetization decreased. Coercivity increased from 975 to 4191 Oe with Al 3+ substitution. An increase in electrical resistivity, coercivity and dielectric characterization made present samples suitable for use in high frequency device applications.

Nickel and cobalt substituted manganese ferrite nanoparticles (NPs) with the chemical composition Ni x Co x Mn 1–2x Fe 2 O 4 (0.0≤x≤0.5) NPs were synthesized by one-pot microwave combustion route. The effect of co-substitution (Ni, Co) on structural, morphological and magnetic properties of MnFe 2 O 4 NPs was investigated using XRD, FT-IR, SEM, VSM and Mossbauer spectroscopic techniques. The cation distribution of all products were also calculated. Both XRD and FT-IR analyses confirmed the synthesis of single phase spinel cubic product for all the substitutions. Lattice constant decreases with the increase in concentration of both Co and Ni in the products. From 57 Fe Mossbauer spectroscopy data, the variations in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values with Mn 2+ , Ni 2+ and Co 2+ substitution have been determined. While the Mossbauer spectra collected at room temperature for the all samples are composed of magnetic sextets, the superparamagnetic doublet is also formed for MnFe 2 O 4 and Ni 0.2 Co 0.2 Mn 0.6 Fe 2 O 4 NPs. The magnetization and Mossbauer measurements verify that MnFe 2 O 4 and Ni 0.2 Co 0.2 Mn 0.6 Fe 2 O 4 NPs have superparamagnetic character. The saturation and remanence magnetizations, magnetic moment and coercive field were determined for all the samples. Room temperature VSM measurements reveals saturation magnetization value close to the bulk one. It has been observed that the saturation magnetization and coercive field increase with respect to the Ni and Co concentrations.

CoCr x Fe2−x O4 (0.0 ≤ x ≤ 1.0) nanoparticles were synthesized by a microwave combustion method and the effect of Cr3+ substitution on structural, morphological, and magnetic properties of CoFe2O4 was studied. The structural, morphological, and magnetic properties of the products were determined and characterized in detail by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometer (VSM). Cation distribution of calculations confirmed the B site (octahedral site) preference of substituted Cr3+ ions. X-ray analysis showed that all compositions crystallize with a cubic spinel-type structure. The lattice parameter decreased from 8.384 to 8.362 A with increasing Cr content. The average crystallite size was found in the range of 30.6–45.4 nm. Magnetization measurements showed that saturation magnetization of products decreases with the increase of the Cr substitution (x).

MnCrFeO 4 ferrites, where Fe 3+ ions stepwise replaced by Gd 3+ ions with a chemical formula MnCrGd x Fe 1−x O 4 (x = 0.0, 0.05, 0.1 and 0.15) were synthesized by employing sol–gel auto combustion method. Crystal structure, nanocrystalline nature of particles, magnetic properties and dielectric properties were investigated by energy dispersive spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and pulse field magnetization techniques. The phase identification of the materials by XRD reveals that the materials formed in the cubic spinel phase with small amounts of GdFeO 3 . TEM observation shows that some of the spherical nanocrystals are transformed in needle-like shape structure upon Gd 3+ substitution. Saturation magnetization and observed magnetic moment are found to increase with Gd 3+ substitution for x ≤ 0.1, obeying Neel's two sublattice model and decreases thereafter, showing existence of non-collinear spin interaction that gives rise to the Yafet–Kittel (θ YK ) angles. Coercivity increased with the increasing doping of Gd 3+ ions in Mn–Cr ferrite. Frequency dependent dielectric constant decreased with Gd 3+ ions substitution, these results were discussed in the light of Maxwell–Wagner type interfacial polarization.

Nanoparticles of Ho3+ substituted in Co–Zn ferrites were synthesised by sol–gel method. The phase formation of these samples has been confirmed by X-ray powder diffraction technique. XRD Rietveld refinement carried out using the FULLPROF program shows that the Co–Zn ferrite retains its single phase cubic structure with space group Fd3m for x ≤ 0.05. Occupancy of the cations is explained on the basis of site preference, size and valance of the substitution cations. The nanostructure and morphology of prepared samples were investigated by field emission scanning electron microscopy and transmission electron microscopy. The elemental percentage of the constituent ions was determined using energy dispersive spectroscopy. The magnetic interactions among the nanoparticles were analyzed by employing a temperature dependent vibration sample magnetometer, field cooled (FC)/zero field cooled (ZFC) measurements. The ZFC and FC curves diverge below the blocking temperature exhibiting a ZFC cusp at 195–225 K. The saturation magnetization of Co–Zn ferrite increased linearly with Ho3+ substitution for x ≤ 0.05 and almost remains constant thereafter. The frequency dependence of the AC susceptibility measurements was performed on the sample. It shows a peak at around spin freezing temperature, with the peak position shifting as a function of driving frequency, indicating a spin-glass-like transition of the sample.

M-type barium hexaferrites Ba1−xCoxFe12O19 (x=0.0–1.00 with steps of 0.25) were synthesized by sol–gel autocombination method and were post-annealed at relatively low temperature at 600 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy, infrared spectroscopy and vibrating sample magnetometry. Crystal transformed from pure Ba-hexaferrite to spinel with Co2+ substitution. Results of scanning electron microscope show that the grains are regular and well-defined structured. Infrared spectra support the nature and crystal symmetry that obtained from X-ray diffraction pattern study. Magnetization results show that saturation magnetization and magneton number decreased whereas coercivity increased for x>0.50 Co2+ doping.

The Zn-Zr co-substituted cobalt ferrite nanoparticles (CoZnxZrxFe2-2xO4, x = 0.0˗0.4) were synthesized by sol gel auto combustion route. The formation of cubic phase of Co ferrite was revealed from the X-ray diffractograms of the powder samples. The additional α-Fe2O3 and ZrO2 phases were occurred for ≥20% Zn-Zr substitution. The lattice parameters obtained by extrapolating Nelson–Riley function shows increase in its values with the Zn-Zr substitution. The particle size shows increasing trend with the Zn-Zr substitution. The cation distribution obtained from the Rietveld refinement of XRD estimate the equal preference of Zn ons preferred tetrahedral A site whereas most of the Zr ions occupy octahedral B site. The decrease in Fe ions with the Zn-Zr substitution resulted in the decrease in coercivity and saturation magnetization of the ferrites. Zero field cooled and field cooled magnetization plots of the ferrites reveals the ferromagnetic behaviour of the prepared ferrite samples. The blocking temperature does not vary significantly with the varying Zn-Zr substitution. The Mossbauer study confirms the weakening of the magnetic linkages between cations at A and B sites, due to the substitution of non-magnetic Zn-Zr ions for magnetic Fe ions. The decrease in coercivity with moderate saturation magnetization could make this material suitable for electronic devices.

Slimani, Yassine/0000-0002-2579-1617; Yasin, Ghulam/0000-0001-8794-3965 WOS:000548698400011 Green and facile process for Ni0.4Cu0.2Zn0.4Fe2-xEuxO4 (x = 0.00-0.10) spinel ferrite nanoparticles (SNPs) prepared via ultrasonic irradiation (without any post annealing process) has been deeply investigated. The influence of Eu3+ substitutions on the structure, morphological, optical, magnetic, electrical and dielectric traits of NiCuZn SNPs was assessed. Tauc plots revealed direct optical band gaps in a very tight interval of 1.86-1.90 eV. Magnetization measurements exposed a superparamagnetic behavior at room temperature and below the blocking temperature (T-B) a superparamagnetic-ferromagnetic transition was noticed. The saturation magnetization (M-s) value is highest for pure Ni0.4Cu0.2Zn0.4Fe2O4 (i.e. x = 0.00) SNP with M-s similar to 58.9 emu/g at room temperature. The saturation magnetization (M-s) declines with rising Eu3+ substituting content. AC conductivity decreases as a function of exponent power base law. Maximum variation in dc conductivity is observed to be around the substitution ratio of x = 0.02. It is found that activation energy is highly dependent on both Eu ions substitution ratios and temperature ranges. The frequency dependence of dielectric functions is explained by Koop's models based on Maxwell-Wagner theory.

Erbium nickel-ferrite (NiErxFe2−xO4 where 0.00 ≤ x ≤ 0.05) nanofibers were prepared by a sol–gel electrospinning process utilizing polyvinylpyrrolidone (PVP) polymer (MW: 40.000). Nanofibers of as-electrospun nickel-ferrite with erbium substitution were calcinated in air at 700 °C for 6 h. After calcination, microscopy analysis indicated uneven nanofiber surfaces that were formed from grains. An increase in erbium concentration in the structure yielded an increase in the lattice parameters and the cell volume, but a decrease in the crystallite size. Elemental erbium, nickel, iron, and oxygen were present in the electrospun NiErxFe2−xO4 nanofibers with no impurities. The magnetic properties were examined via magnetization against magnetic field (M-H) measurements. The M-H curves of all prepared NiErxFe2−xO4 nanofibers were measured at two different temperatures; room temperature (T = 300 K) and low temperature (T = 10 K) throughout H of ±70 kOe. The values of M s (saturation magnetization), M r (remanence), H c (coercivity), SQR = M r /M s (squareness ratio), and (magnetic moments) were determined. The prepared set of nanofibers showed soft ferrimagnetic behavior at both 300 and 10 K. At both measured temperatures M s improved with increasing Er3+ concentration up to x = 0.02, then it decreased with further increase in the Er3+ content.

Mn0.5Zn0.5DyxFe2−xO4 (x ≤ 0.03) nanoparticles (NPs) were fabricated by using Ultrasonic irradiation using UZ SONOPULS HD 2070 ultrasonic homogenizer (frequency of 20 kHz and power of 70 W). Structural and morphological analyses were performed via XRD (X-ray powder diffractometer), TEM (Transmission electron microscopy) and SEM (Scanning electron microscopy). XRD presented the formation of Mn-Zn ferrite with average crystal size in 11 to 18 nm range. Direct optical energy band gaps (Eg) were specified applying diffuse reflectance investigations. Eg values are in a small band range of 1.61–1.67 eV. Low (10 K) and room temperature VSM data were recorded applying ±90 kOe external magnetic field. All samples exhibit superparamagnetic properties at RT. Magnetization parameters significantly increase due to coordination of Dy3+ rare earth ions. Magnetic moment per molecule (nB) increases from 0.952 μB to 1.137 μB and from 2.312 μB to 2.547 μB at RT and at 10 K data respectively. 10 K coercivity (Hc) values decrease from 260 Oe to 43 Oe. All samples have squareness ratios (SQR) of 0.231–0.400 range assigning the multi-domain structure at 10 K. ZFC-FC magnetization curves that were registered for two selected samples exhibit a divergence and a sharp drop below their Tpeak positions. This event is typically correlated to the collective freezing of system and spin-glass-like phase. Real part AC susceptibility data slightly shift toward high temperature regions with increasing frequencies. Critical Slowing Down (CSD) model explained the spin dynamics of interacting NPs consistently with literature and proved the spin-glass behavior of samples at low temperatures.

In this study, bimetallic (Cu–Mn) substituted SrFe12O19 hexaferrites [Sr1−2xMnxCuxFe12O19 (0.0 ≤ x ≤ 0.1)] were synthesized via sol–gel auto-combustion approach. The effect of bimetallic substitution on structure, morphology and magnetism of SrFe12O19 was investigated. SEM images divulge the nano-size of the prepared products with speck morphology. X-ray powder diffraction analysis affirmed their complete conversion to SrFe12O19 hexagonal crystal phase. The results from 57Fe Mossbauer suggested that all five important sextets of Sr1−2xMnxCuxFe12O19 hexaferrites effected due to the substitution of Cu and Mn ions. Cation distribution calculation showed that as the percentage of Mn and Cu increased in Sr1−2xMnxCuxFe12O19 (0.0 ≤ x ≤ 0.1), particularly for x = 0.03 the relative area of 12k and 4f2 site increased. This indicates that Fe ions are migrated towards 12k and 4f2 octahedral site.

Nanospinel Li 2x Cu 1-x Al y Fe 2-y O 4 ferrites with composition x = y = 0.0, 0.2, 0.3 and 0.4, were successfully synthesized via hydrothermal method. The effect of co-substitution (Li and Al) on structural, morphological and magnetic properties of CuFe 2 O 4 nanoparticles were investigated using Powder X-ray Diffraction (XRD), Fourier-Transform Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM) and Mossbauer spectroscopic techniques. The cation distribution of all composition was calculated. Both XRD and FT-IR analyses confirmed the synthesis of single-phase spinel cubic product for all the substitutions. Mossbauer investigation showed that the Li 1+ and Al 3+ ions occupied B-sites. Nonetheless, some amounts of Li 1+ occupy A-site. The magnetization hysteresis loops M (H) , revealed that the final products with x, y = 0.0, 0.3 and 0.4 exhibit superparamagnetic (SPM) behavior at room temperature, however the composition x, y = 0.2 displays a ferromagnetic-like (FM) behavior. The saturation magnetization (M s ) reduces with rising the Li and Al contents. Compared to pristine CuFe 2 O 4 spinel, the remanent magnetization (M r ), coercive field (H c ) and the magneto-crystalline anisotropy fields (H a ) improved for products synthesized with x, y = 0.2 and then decrease for x, y = 0.3 and 0.4. The squareness ratio M r /M s are less than 0.500, which suggest the single domain nanoparticles with uniaxial anisotropy for Li 2x Cu 1–x Al y Fe 2-y O 4 (0.0 ≤ x, y ≤ 0.4) nanoparticles. The magneto-crystalline anisotropy constant (K eff ) value is improved for Li 0.8 Cu 0.6 Al 0.2 Fe 1.8 O 4 (i.e. x, y = 0.2) magnetic nanoparticles and then decreased for higher Li and Al contents, due to the replacement of Cu and Fe ions with respectively Li and Al ions.

Nano structured indium substituted NiCuZu ferrites with chemical composition Ni05Cu0.25Zn0.25 Fe2-xInxO4 (0.0

The Cr3+ ions doped multi-oxide ZnFe2−xCrxO4 ferrite nanoparticles have been synthesized by chemical co-precipitation method. Site occupancies of Zn2+, Cr3+ and Fe3+ ions were analyzed using X-ray diffraction data and Buerger's method. The effect of the constituent phase variation on the magnetic hysteresis behavior was examined by saturation magnetization which decreases with the increase in Cr3+ content in place of Fe3+ ions at octahedral B-site. Typical blocking temperature (TB) around 90 K was observed by zero field cooling and field cooling magnetization study. Room temperature Mossbauer spectra show two paramagnetic doublets (tetrahedral and octahedral sites). The isomer shifts of both doublets decrease whereas quadrupole splitting and relative area of tetrahedral A-site increases with increasing Cr3+ substitution. The dielectric constant (measured on compositions x=0, 0.4, 0.8 and 1.0) increases when the temperature increases as in the semiconductor. This behavior is attributed to the hopping of electrons between Fe2+ and Fe3+ ions with a thermal activation.

The nanocrystalline Mg0.5Zn0.5−xCoxFe2O4 (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) ferrites have been synthesized by sol–gel auto ignition method. Rietveld refinement of X-ray diffraction (XRD) patterns of all concentrations show mixed cubic spinel structure. The lattice constant values infer decreasing trend from 8.420 to 8.392 A with the substitution of Co2+. The crystallite size calculated from Scherer formula lies in the range between 28 and 37 nm which confirms the nanocrystalline nature of synthesized samples. In order to study the morphology and phase structure of the synthesized samples, samples were examined by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) confirmed the homogeneous and well defined surface morphology of the synthesized samples. The elemental analysis as obtained from energy dispersive X-ray (EDAX) is in close agreement with the expected composition from the stoichiometry of reactant solutions used. The valence states of the Co2+ ions have been confirmed with the help of X-ray photoelectron spectroscopy. Magnetization results obtained from the vibrating sample magnetometer (VSM) confirm that the substitution of Co2+ for Zn2+ caused an increase in the saturation magnetization and coercivity. The dependence of Mossbauer parameters, viz., line width, isomer shift, quadrupole splitting and hyperfine magnetic field on Co2+ substitution have been analyzed. Cation distribution estimated from XRD and Mossbauer spectroscopy are in good agreement with each other. The frequency dependent dielectric properties were studied by measuring dielectric constant (e׳) and ac conductivity (σac) at 300 K in the frequency range of 50 Hz–5 MHz. The highest value for e׳ and σac is observed for x=0.5.

Nanocrystalline ferrite powders of Co2 + substituted Li0.5Cr0.5Fe2O4 were synthesized by sol-gel auto-combustion method. The samples were obtained by annealing at relatively low temperature at 600 °C and investigated by XRD, TEM, IR, magnetization, and dielectric and resistivity measurements. Lattice parameter, X-ray density, crystallite size and bulk density are found to increase, whereas specific surface area and porosity size showed the decreasing trend with the Co2 + substitution. Splitting of major absorption bands related to Li+ substituted ferrites was observed in IR spectra. Site occupancy is obtained from XRD and the variation of the cation distribution has been discussed on the basis of site preference of the substituting cations. Substitution of the magnetic Co2 + ions considerably improved the magnetic properties; as reflected by the advancement in the values of saturation magnetization and coercivity. The variation of the magneton number with the Co2 + content is satisfactorily explained on the basis of Neel's collinear spin ordering model. Resistivity plots show the semiconducting nature of the synthesized samples. The observed variation in resistivity is explained by Verwey hopping mechanism. The dielectric constant and dielectric loss tangent were also studied as a function of temperature.

Li + substituted CoFe 2 O 4 with the chemical formula Li 3 x CoFe 2− x O 4 were synthesized by sol–gel auto combustion method. The synthesized samples were annealed at 600 °C for 4 h. X-ray diffraction data were used to evaluate the structure of the prepared samples. Spinel ferrite phase of CoFe 2 O 4 changes to ordered like lithium ferrite phase with increase in L i+ substitution. Lattice constant increases whereas particle size found to decrease with Li + substitution. Infrared spectroscopy also confirmed the phase transition of CoFe 2 O 4 after the incorporation of lithium ions. Substitution of Li + ions for Fe 3+ caused a decrease in the saturation magnetization from 69.59 emu/g to 47.71 emu/g and the coercivity increased from 647 Oe to 802 Oe. Resistivity and dielectric properties shows inverse relation to each other.

The role of Bi2O3 addition on the structural and magnetic properties of NiCuZn-Tb ferrites with composition Ni0.5Cu0.25Zn0.25Tb0.1Fe1.9O4+xBi2O3 has been investigated, where values of x (in wt %) are 0, 1, 2 and 3. Samples were prepared by the sol-gel auto combustion synthesis. The crystallographic, structural and magnetic properties of the samples were investigated by X-ray diffraction (XRD), scanning electron micrography, vibrating sample magnetometer and permeability measurements. Cubic spinel structure was observed from the XRD pattern for all the samples, implying that the Bi2O3 additives did not form a visible second phase in ≤ 2 wt% of Bi2O3. Microstructural studies showed that Bi2O3 forms a liquid-like phase and promotes the grain growth. The average grain size increased for ≤ 2 and then decreased for > 2 wt% of Bi2O3 content. The maximal grain size appears with 2 wt% Bi2O3. These characteristics evidently affect the magnetic properties, such as saturation magnetization (Ms) and permeability of the NiCuZn-Tb ferrites. Bi2O3 increase the Ms, bulk density (dB) and permeability effectively, while excessive Bi2O3 concentration results in the abnormal grain growth and decrease of Ms and dB.

Magnetic, optic and microstructural properties of ultrasonically synthesized CoEuxFe2−xO4 (x ≤ 0.1) nanoferrites (NFs) have been examined in this study. After sonochemical synthesis, XRD and FT-IR analyses confirmed the purity, the structure (cubic spinel structure and Fd3m space group) and the spectral properties of the spinel ferrite samples. The spherical morphology and chemical compositions of the products were observed via transmission and scanning electron microscopes along with EDX and elemental mapping. Percent diffuse reflectance (%DR) was used for optical investigation. Optical band gaps (Eg) were estimated utilizing Kubelka-Munk theory and Tauc equation. Eg values are in a narrow band of 1.34 to 1.44 eV. The magnetic parameters like Ms (saturation magnetization), SQR = Mr/Ms (squareness ratio), n B (magnetic moment), Hc (coercivity) and Mr (remanence) have been evaluated by analyzing measurements of magnetization versus magnetic field performed at room (RT; T = 300 K) and low (T = 10 K) temperatures. It is showed that the different produced CoEuxFe2−xO4 (0.00 ≤ x ≤ 0.10) nanospinel ferrites present superparamagnetic (SPM) nature at RT. At low temperature, the various produced CoEuxFe2−xO4 (x ≤ 0.08) nanospinel ferrites display ferrimagnetic (FM) nature. With exception, the x = 0.10 sample exhibit SPM behavior at T = 10 K. It is noticed that the Eu3+ substitutions alter in a significant way on the magnetic data. A decreasing trend in the Ms, Mr and n B values was noted with Eu3+ substitutions.

In this study, Tm3+ ion substituted NiCuZn nanospinel ferrites, Ni0.3Cu0.3Zn0.4TmxFe2−xO4 (0.0 ≤ x ≤ 0.10), have been synthesized sonochemically. The structural, spectroscopic, morphological, optic and magnetic investigation of the samples were done by X-ray powder diffractometry (XRD), Fourier transform infrared spectrophotometry (FT-IR), UV–Vis diffused reflectance (%DR) spectrophotometry, transmission and scanning electron microscopies (TEM and SEM) along with EDX, Vibrating sample magnetometry (VSM), respectively. The purity of prepared products were confirmed via XRD, FT-IR, EDX and elemental mapping analyses. The analyses of magnetization versus M(H) (applied magnetic field) were performed at 300 and 10 K. The following magnetic parameters like Ms (saturation magnetization), SQR = Mr/Ms (squareness ratio), n B ( magnetic moment), Hc (coercivity) and Mr (remanence) have been discussed. M(H) loops revealed superparamagnetic property at RT and soft ferromagnetic nature at 10 K. It is showed that the Tm3+ substitutions significantly affect the magnetizations data. A decreasing trend in the Ms, Hc, Mr, and n B values was detected with Tm3+ substitution.

We have synthesized heterovalent Mn2+–Si4+ substituted MnCrFeO nanoparticles with a nominal composition Mn1+xSixCrFe1−2xO4 (x = 0.0–0.3) via sol–gel auto-combustion method. X-ray diffractometer, transmission electron microscopy, magnetization measurements were used to study the effects of Mn2+–Si4+ heterovalent ions on the structural and magnetic properties of MnCrFeO. As a result, it was found that the Mn2+–Si4+ ions affect the crystalline structures and magnetic properties of MnCrFeO. X-ray diffraction pattern showed that the samples have the single phase cubic spinel structure of which the lattice constant slightly increased upon Mn2+–Si4+ substitution. The mean crystallite size of the samples was in the range of 21–27 nm as deduced from the XRD line broadening. Cation distribution was estimated using XRD data and it shows that Mn2+ and Si4+ ions prefer tetrahedral A-site. Magnetic measurement shows that saturation magnetization and magneton number decreased with Mn2+–Si4+ substitution with the formation of a collinear spin arrangement.

Nanoparticles with compositions of Cu0.4−0.5xCd0.2Ni0.4+xFe2−0.5xO4 (0.0 ⩽ x ⩽ 0.5) were successfully synthesized by a citrate–nitrate sol–gel auto combustion route. The combusted powder was calcinated at four hours in a furnace and then slowly cooled to room temperature. The analysis methods of FTIR, XRD, FESEM, VSM and dielectric measurements were used to characterize prepared magnetic particles. The effect of Ni2+ substitution on structural, magnetic and dielectric properties of Cu–Cd ferrite nanoparticles was studied. The comprehensive studies on compositional and frequency dependent dielectric properties were carried out by means of AC conductivity (σac), imaginary dielectric constant (e′′), loss tangent (tan δ), impedance and dielectric modulus (real and imaginary) measurements in frequency range of 50 Hz–5 MHz at room temperature. The structural properties investigated by using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. X-ray diffraction pattern and FTIR results revealed that synthesized samples are in single phase. It is observed that the dielectric constant (e′′) and dielectric loss (tan δ) value decreases with increase in Ni2+ concentration (x). At low frequency the Maxwell type interfacial polarization was observed. Magnetization measurement shows that the Curie temperature of the samples increases with Ni2+ concentration, which is explained by a change in the A–O–B super exchange interaction.

A series of spinel ferrites, Li0.5Co1.5xFe2.5−xO4, with x = 0.0, 0.25, 0.50, 0.75 and 1.0 were successfully synthesized by sol–gel auto combustion method, aiming to study the relationship between structural and magnetic interactions related to the concentration of the substituted cobalt cations. X-ray diffraction measurements were employed for analyzing the structure, lattice parameter, density, porosity and crystallite size of the prepared samples. Samples have the cubic spinel structure with a small amount of α-Fe2O3 and γ-Fe2O3. As the Co2+ ions increases, hematite and maghemite phases disappear and the crystals form the single phase spinel structure with the cation ordering on octahedral sites. Lattice constant (a) increases from 8.331 to 8.423 A with increase in Co2+ substitution. Particle size estimated from the transmission electron microscopy images, and is ranging from 12 to 23 nm. Infrared spectroscopy measurements were carried out to study the band position and structure of the sample. Saturation magnetization decreased linearly from 41.21 to 28.84 A m2/kg with an increase in Co2+ content. It was found that coercivity increased with the Co2+ substitution from 8678 to 75636 A/m. The samples were zero field cooled to 100 K. Typical blocking effects were observed below about 253 K. Curie temperature (TC) were obtained from AC susceptibility and permeability measurements shows the decreasing trend with Co2+ substitution, indicating the weakening in A–B interactions. Permeability decreased with the increase in Co2+ substitution due to the combine effect of magnetization and magnetocrystalline anisotropy.

Samples of Zr4+ and Zn2+ co-substituted Li0.5Fe2.5O4 nanoparticles were prepared by the sol–gel auto-combustion method. The samples were obtained by annealing at relatively low temperature at 600 °C and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM) and Fourier transform infrared (FT-IR) spectroscopy. Lattice parameter, X-ray density, specific surface area and porosity were found to increase, whereas bulk density and crystallite size showed the decreasing trend with the Zr4+ and Zn2+ substitution. Cation distribution estimated from XRD results suggests that Zn2+ and Li+ occupy tetrahedral A- and octahedral B-site respectively, whereas Zr4+ and Fe3+ occupy both the available sites. The FT-IR spectra show two major absorption bands at 715–749 cm−1 (ν1) and 484–507 cm−1 (ν2) related to spinel structure of ferrite. Magnetization results exhibit collinear ferrimagnetic structure for x ≤ 0.2, and changed to the non-collinear for x > 0.2. Observed and calculated magneton number shows discrepancy in their values that gives rise to Yafet–Kittle angle for x > 0.2.

Nanoparticles of Cu–Cd–Ni–FeO 4 were synthesized by the auto-combustion process using a modified citric acid method. Antibacterial activity, structural, dielectric and magnetic properties were investigated. An assay showed the broad spectrum antibacterial activity of Cu–Cd–Ni–FeO 4 against Gram positive and Gram negative pathogenic bacterial strains. The existence of single phase cubic spinel structure of ferrites was confirmed by X-ray diffraction measurement. Fourier transform infrared spectroscopy shows the two main absorption bands at lower frequency region. Surface morphology and compositional features were studied by scanning electron microscopy and energy dispersive X-ray spectroscopy analysis, respectively. Results indicated that the nanosize particles greatly influenced the antibacterial activity, as well as structural, dielectric and magnetic properties of the samples. Magnetic measurements of the samples were carried out by means of vibrating sample magnetometry and Mossbauer spectroscopy. Magnetic properties are strongly affected by Ni 2+ substitution.