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Magnesium nanoferrites are gaining a lot of scientific attention because of its magnificent dielectric characteristics such as large dielectric constant with minute dielectric losses, which make it suitable for potential applications such as high frequency, microwave devices, switching devices, power, magnetic storage devices, and many more. A series of manganese- and silver-substituted magnesium nanoferrites with the chemical composition Mg1−yMnyAgxFe2−xO4 (0.1 ≤ y ≤ 0.4, 0.0 ≤ x ≤ 0.3) were synthesized via sol–gel auto-combustion technique for reporting the electrical and dielectric study of synthesized specimens. In the present investigation, the dc resistivity (ρ) of prepared nanoferrites goes on decreasing as a function of Ag+ and Mn2+ concentrations extensively indicate its semi-conductor behavior. From the dielectric measurements, dielectric constant (∈′) increases with the increase in frequency, whereas the dielectric loss tangent (tan δ) shows an inverse behavior with the increasing frequency, respectively. In relation with the dielectric investigations, AC conductivity (σac) shows similar behavior to that of dielectric constant. Therefore, such materials of high dielectric constant with minute dielectric losses make it suitable for the power application.

Z-type nanohexaferrites has attracted substantial attention in the field of materials science especially in the research areas of high frequency and microwave devices applications due to their excellent magnetic properties in comparison with the spinel ferrites. A series of Ba1.5Sr1.5Co2−xYxMnyNizFe24−y−zO41 (x = 0.0, 0.05, 0.10, 0.15, 0.20; y = z = 0.0, 0.25, 0.50, 0.75, 1.00) Z-type hexaferrites were fabricated with the help of sol–gel auto-combustion method in order to achieve its better microstructural and magnetic properties. The crystallographic structure of prepared specimens was characterized by XRD which revealed the presence of Z-type single-phase hexagonal structure with some additional phases accompanied by P63/mmc space group. The average particle size calculated by Scherrer formula was found to be in the range of 40–55 nm. The FTIR spectrum of synthesized specimens was observed in the range of 400–600 cm−1 which confirms our microstructural results to a great extent. From the M–H hysteresis loops, magnetic parameters such as saturation magnetization (Ms) (44.04–35.59 emu/g) and coercivity (Hc) (42.3–248.96 Oe) were measured and it was observed that the synthesized specimens exhibit excellent characteristics of soft ferrite which make it suitable for the multilayer chip inductors, electromagnets, and magnetic storage devices applications.

Ba0.7Nd0.3CdxFe12−xO19 nanohexaferrites have been synthesized by sol–gel method. Rietveld refined X-ray diffraction study predicted the single phase formation with c/a ratio 3.93. The magnetic and dielectric properties have been significantly improved with the addition of cadmium ions. An increase in the saturation magnetization (65.01–103.46 emu/g) and retentivity (32.15–51.90 emu/g) has been observed with the incorporation of cadmium ions and incredible enhancement in the saturation magnetization, up to 103.46 emu/g, is observed for x = 0.3. The value of magnetization so obtained is the prime achievement of the present work. The dielectric constant (eʹ), dielectric loss (eʺ), magnetic permeability (μʹ) and magnetic loss (μʺ) are investigated over GHz frequency range. The results are explained in the light of Maxwell–Wagner model. Further, the Mossbauer spectroscopic analysis of the synthesized nanohexaferrites is also carried out to support the magnetic study.

In this present work, we have done the comparison of raman spectra of hard ferrite i.e. Ba0.7Nd0.3Cd0.5xIn0.5xFe12-xO19 (x = 0.0, 0.2, 0.3) and soft ferrite i.e. Mg1-xMnxAgyFe2-yO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5, y = 0.0, 0.1, 0.2, 0.3, 0.4) which defines the novality and achievement of this work. These ferrite based nanomaterials were synthesized with the aid of sol-gel auto-combustion method in order to analyze Raman spectra carried with 514.5 nm laser of argon ion (50 mW) by using Renishaw inVia Reflex micro-Raman spectrometer. The Raman spectra of synthesized Mg1-xMnxAgyFe2-yO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5, y = 0.0, 0.1, 0.2, 0.3, 0.4) and Ba0.7Nd0.3Cd0.5xIn0.5xFe12-xO19 (x = 0.0, 0.2, 0.3) ferrites confirmed the formation of five active Raman vibrational modes (A1g + Eg+3T2g). Out of this, Raman spectral analysis of Mg1-xMnxAgyFe2-yO4 (x = 0.1, 0.2, 0.3, 0.4, 0.5, y = 0.0, 0.1, 0.2, 0.3, 0.4) nanomaterials confined that Eg mode is found in the range of 194.74–212.77 cm−1, T2g vibrational mode is found to be in the range of 326.17–339.58 cm−1, 482.27–587 cm−1 and 608.84–614.02 cm−1 whereas A1g configuration mode is found to be in the range of 685.47–701.52 cm−1. In addition to this, Raman spectral analysis of Ba0.7NdO.3Cd0.5xIn0.5xFe12-xO19 (x = 0.0, 0.2, 0.3) nanohexaferrites consists of five Raman active vibrational modes in the range as ν1 = 329.02–334.70 cm−1, ν2 = 410.33–410.90 cm−1, ν3 = 522.06–524.65 cm−1, ν4 = 612.52–616.66 cm−1 and ν 5 = 679.97–685.16 cm−1. The Raman spectra of both the compositions continuously indicates the symmetric and anti-symmetric behaviour of the band position of spinel and hexagonal magnetic nanomaterials.

In the present review paper, we have explained the structure of Y-type hexagonal ferrite and various synthesis techniques. This paper also includes structural, electrical, magnetic properties and applications of Y-type hexaferrites and focusses on their use in antenna applications and microwave absorbing characteristic materials. Ferromagnetic nature of hexaferrites cause the induction of magnetisation within the crystal structure, which divide them into two groups: First with easy axis of magnetisation is known as uniaxial hexaferrites and second is known as ferroxplana having easy plane of magnetisation. The excellent magnetic properties of Y-type ferrites make them useful in the devices operating at high frequency range. The persistence of high refractive index upto 1 GHz enables these hexagonal ferrites useful in UHF antenna designs with small dimensions. The doping in Y-type hexaferrites affect all the properties. Current developments in Y-type hexaferrites will be explained in detail in the review of literature related to Y-type hexaferrites for the last 25 years, i.e. from 1994 to 2019 in this review paper.

In the present work, we have successfully prepared Cu2+doped Mg-Mn nanoferrites using solution combustion (SC) method and we have mainly focused on the structural study of Mg0.9Mn0.1CuxFe2-xO4 nanoferrite. There are many structural factors which affects the properties of the ferrites like particle size, stress, strain etc. The strain, particle size, stress and energy density have been analysed with the help of Williamsons-Hall Model using Uniform Deformation Model (UDM), Uniform Stress Deformation Model (USDM) and Uniform Deform Energy Density Model (UDEDM). The stress, strain, particle size & energy density have been found to reduce while lattice parameter, achieved from the Nelson-Riley plots, has been found to rise with the replacement of Fe3+ ions by Cu2+ions.

In the present work, silver doped Mg–Mn ferrite nanoparticles (Mg1-yMnyAgxFe2-xO4; y = 0.1, 0.2, 0.3, 0.4, 0.5 and x = 0.0, 0.1, 0.2, 0.3, 0.4) are synthesized by using sol-gel technique and are characterized by x-ray diffraction (XRD), energy dispersive x-ray (EDX) analysis, field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and Mossbauer spectroscopy. The single phase formation of the prepared ferrite nanoparticles is depicted by XRD study and the crystallite size as well as lattice parameter are found to increase (51–65 nm) and (8.367–8.384 A) with the addition of silver ions. EDX study confirmed the compositional formation of the prepared ferrite nanoparticles. FESEM study depicted the clear crystalline nature of the nanoferrites with cubic structure. FTIR study revealed a decrease in bond length of M-O at tetrahedral (A) site and an increase in bond length between M-O at octahedral (B) site. The value of saturation magnetization is found to be 25.31 emu/gm for y = 0.1, x = 0 with highest value 30.26 emu/gm for ferrite with composition y = 0.4, x = 0.3. The cations distribution has been estimated using the XRD and magnetization techniques.

Precise studies of cadmium and indium doped barium hexagonal ferrites having chemical composition Ba0.7Nd0.3Cdx/2Inx/2Fe12-xO19 (x = 0.0, 0.1, 0.2, 0.3) have been performed by sol-gel auto-combustion method in which ethylene glycol was used as a gel precursor. The structural, morphological, optical, elemental and magnetic properties have been studied by using various techniques like XRD, FESEM, FTIR, EDS and VSM. The XRD patterns shows characteristic (110), (008), (107), (114), (108), (203), (205), (206), (1011), (300), (217), (2011), (220), (2014) peaks along with the presence of secondary phase confirming the formation of hexagonal structure with an average crystallite size of 43–59 nm. FESEM supports the formation of hexagonal, dense and agglomerated nanoparticles. The Vibronic study using infrared radiation was carried by FTIR analysis reveal the various configuration modes with hexagonal symmetry of prepared nanoparticles. The magnetic measurements have been studied at room temperature indicates that saturation magnetization (Ms) and magnetic moment (nB) found to be of range 40–86 emu/g and 7.97–17.23 μB. The precise magnetic studies made it possible to reveal that saturation magnetization (Ms) increases with the cadmium and indium concentration for x = 0.1 and after that it decreases for x = 0.2, 0.3 which may be due to the difference in the magnetic moments of Cd, In and Fe ions. Due to high value of saturation magnetization (Ms), it can be used for applications in the field of high density recording storage devices and also, this magnetic change has been explained on the basis of exchange interactions. The room temperature M o ¨ ssbauer spectra of all the nano-sized materials shows normal Zeeman splitting consisting of six merged line patterns which indicates the formation of ferromagnetic phase that supports the magnetic properties.

The interference of industrial effluents such as dyes, surfactants, metals, polycyclic aromatic hydrocarbons, and pharmaceutical waste has become a severe global problem for human health due to their carcinogenic, mutagenic, and toxic properties. Ferrites were considered promising photocatalysts for the degradation of organic and inorganic dyes. This study mainly focused on improving the photocatalytic performance of MnFe2O4 nanoferrites via doping of Zn2+ and La3+ ions. The zinc and lanthanum substituted Mn1−xZnxLayFe2−yO4 nanoferrites were prepared by the sol-gel auto-combustion technique for the degradation of organic textile malachite green dye (MGD) under the natural solar irradiation. The synthesized nanoferrites were investigated for their structural properties, surface morphology and elemental analysis, optical studies, magnetic properties, and photocatalytic performance by XRD, FESEM/EDX, FTIR/Raman spectrum, vibrating sample magnetometer, and UV-visible spectrophotometer, respectively. The substitution of zinc and lanthanum improved the photocatalytic efficiency of nanoferrites, and about 96% of MGD was degraded by Mn0.97Zn0.03La0.04Fe1.96O4 after 60 min of irradiation. The results showed the pseudo-first-order kinetics for dye degradation using undoped and Zn/La-doped MnFe2O4 photocatalysts.

After the discovery of hexagonal ferrites or hexaferrites, it has been become important materials commercially and technically to study which is still growing on. In this article, we have reviewed about the M-type hexaferrites including their structural, synthesis techniques and important magnetic properties. The role of experimental synthesizing techniques adopted for preparation of M-type hexaferrites on the various parameters studied in this review paper. The substitution of holonium in BaM ferrite reduces the value of coercivity but not saturation magnetization and ramanence and the cobalt-titanium substituted ferrites were the most important M-type ferrites in the field of application in microwave properties and magnetic field industry.

Herein, we report synthesis of graphitic carbon sand composite (GSC) and bentonite (BT) supported superparamagnetic MnFe2O4 nanoparticles to obtain MnFe2O4/GSC and MnFe2O4/BT nanocomposites. Graphitic carbon sand composite (GSC) was prepared by graphitization of sugar over river sand. The particle size of MnFe2O4/GSC and MnFe2O4/BT was found to be 50 and 60 nm respectively. BET adsorption experiments confirmed mesoporous nature of prepared photocatalysts. Magnetic studies revealed superparamagnetic behavior of MnFe2O4/GSC and MnFe2O4/BT. The band gaps of MnFe2O4/GSC and MnFe2O4/BT were 2.38 and 2.42 eV respectively. Both MnFe2O4/GSC and MnFe2O4/BT exhibited significant photocatalytic activity for the mineralization of ampicillin (AMP) and oxytetracycline (OTC) antibiotics under solar light. Simultaneous adsorption and degradation process (A + P) resulted in higher photodegradation of OTC and AMP. The applicability of power law model indicated intricacies of mineralization process. MnFe2O4/GSC and MnFe2O4/BT displayed significant recycle efficiency and easier recovery of photocatalyst for 10 consecutive catalytic cycles.

A series of Co2Z-type Ba–Sr nanohexaferrites Ba1.5Sr1.5Co2−zHozMnxNiyFe24−x−yO41 (z = 0.0, 0.05, 0.10, 0.15, 0.20, x = y = 0.0, 0.25, 0.5, 0.75, 1.00) have been synthesized using sol–gel auto-combustion synthesis route. The effect of Ho–Ni–Mn substitutions on crystallographic and magnetic properties of synthesized nanohexaferrites was investigated using XRD, VSM, and Mossbauer spectroscopy. Microstructural analysis showed single-phase crystal structures without any impurities and hexagonal with the space group P63/mmc. The average variation in crystallite size ranges from 43 to 60 nm with a slight increase in X-ray density and appreciable decrease in porosity was observed for different dopants. FE-SEM (Nova Nano SEM-450) substantiates the hexagonal structure and HR-TEM images assisted with SAED pattern confirm the crystalline quality and FWHM of the material, which significantly support the XRD results. FTIR spectra showed two characteristic metal stretching peaks in the range of 400–600 cm−1 due to the substitution of Ho–Ni–Mn. Magnetic measurements show maximum magnetic saturation (Ms) at 44.04 emu g−1 and elevated value of coercivity (Hc) 224Oe imparting typical characteristics of soft ferrite with high coercivity. Mossbauer analysis with least squares fit sextets of six distinguishable sites at room temperature for all samples substantially supports the results of VSM. The materials with large coercivity are useful in permanent magnet applications. The prepared composites could be useful for applications in microwave absorbing materials, magnetic storage, and the miniaturization of antennas for wireless communication devices.

Nanocrystalline particles of strontium W-type hexaferrites having chemical composition SrCo2AgxFe16-xO27 (x = 0.0, 0.1, 0.2, 0.3) were synthesized by sol-gel technique. The optical and magnetic study was done by using Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The FTIR spectra consisting of absorption peaks within range of 603.9-607 cm−1 confirmed the formation of hexagonal structure for the prepared samples. From the magnetic hysteresis loops, the four magnetic parameters such as saturation magnetization (Ms), remanent magnetization (Mr), coercivity (Hc) and magnetic moment (nB) were calculated. It was reported that saturation magnetization (Ms) and magnetic moment (nB) increases for lower values of silver dopant (x = 0.0, 0.1, 0.2) but for the highest concentration of silver (x = 0.3), values of these two parameters decreases. Also, the values of coercivity (Hc) were found to be in range of 6-54 Oe indicating soft character of synthesized nanohexaferrites.

Magnetic nanoparticles are of great interest due to structure and composition of materials. MNP consists of cations, e.g., Fe, Ni, Co, Cr, and their oxides, such as magnetite (Fe3O4), maghemite (γ-Fe2O3), hematite (α- Fe2O3), cobalt ferrite (Fe2CoO4), and chromium dioxide (CrO2). Magnetic nanoparticles are gaining interest due to their useful electrical and magnetic properties and applications in magnetic storage, recording media, photo catalysis, and medical diagontics as well as in solar energy applications. Magnetic nanoparticles are regarded as the most practically important and useful due to its simple synthesis and the interesting magnetic characteristics of its nano-sized objects. This review summarizes recent commercial, industrial and bio-engineering applications and brief study of the methods for the preparation of magnetic nanoparticles with a control over the size, morphology and the magnetic properties.

Zinc oxide nanoparticles doped with 5, 10 & 15 mol% of nitrogen contents have been synthesized by sol gel technique. The average particle size was determined from the line broadening of (101) peak of XRD and further verified from SEM. The observed particle size varies from 23 to 15 nm with increase of dopant concentration. The surface morphology of all samples was studied by Scanning Electron Microscopy and shows small agglomeration. The agglomeration increases with increase in doping concentration may be attributed to the strength of vander Waals forces, changes with particle size leads to increase in surface area of nanoparticles. The optical band gap energy was calculated using Tauc’s Plot. The photocatalytic activity of synthesized samples was studied under UV light source (wavelength 380-420 nm) by using methylene Blue (MB). The degradation efficiency of synthesized samples increases with increase in nitrogen dopent is attributable to increase in carrier recombination rate which counteracts the increase activity arises from higher specific area of nanoparticles.

Nano-sized particles of W-type hexaferrites having chemical composition SrCo2AgxFe16-xO27 (x = 0.0, 0.1, 0.2, 0.3) was synthesized by sol gel auto-combustion technique. The structural, morphological and elemental distribution of synthesized nanohexaferrites was studied by using techniques such as XRD, FESEM, EDS. From the XRD analysis, the crystallite size is found to be in the range of 51-61 nm calculated by using Debye-Scherrer formula which means crystallite size increases with increase in silver concentration. FESEM analysis revealed that grains are hexagonal in shape. The EDS spectra of the prepared samples confirming the formation of pure nanohexaferrites and elemental composition infer that no elements except strontium, cobalt, silver, iron and oxygen are present in the synthesized samples.

Adsorbent supported photocatalysis is developing as a potential waste water treatment technology. In this work, NiFe 2 O 4 was supported onto graphene sand composite (GSC) and bentonite (BT) supported to prepare magnetic NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT nanocomposties. Graphene sand composite (GSC) was prepared by graphitization of sugar over river sand. The size of NiFe 2 O 4 /BT and NiFe 2 O 4 /GSC was found to be 50 and 60 nm respectively. Mesoporous nature of prepared photocatalysts was confirmed by BET adsorption/desorption experiments. NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT exhibited ferromagnetic behaviour and could be separated from treated water using external magnetic field. The band gaps of NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT were found to be 2.41 and 2.42 eV, respectively. The adsorption and photocatalytic activity of NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT was tested for the mineralization of ampicillin (AMP) and oxytetracycline (OTC) antibiotics under solar light. The adsorption process had significant effect on the mineralization of AMP and OTC. Simultaneous adsorption and degradation (A + P) process were the most efficient for antibiotic degradation. The complete mineralization of antibiotics was obtained using NiFe 2 O 4 /GSC/A + P and NiFe 2 O 4 /BT/A + P catalytic processes. The kinetics of mineralization were explored using power law model. Magnetically recoverable NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT are recyclable and displayed significant recycle efficiency and quick recovery for 10 consecutive catalytic cycles.

BaLa x Fe 12− x O 19 (0.05≤ x ≤0.25) nanohexaferrites were synthesized by sol–gel auto combustion method. X-ray diffraction study revealed the hexagonal structure of the synthesized nanoferrites without any secondary phase and Rietveld analysis confirmed the P63/mmc space group. The crystallite size was observed to increase (49–63 nm) with the increasing substitution of La 3+ ions. The particle size was observed to be in the range 49–63 nm. The remarkable increase in saturation magnetization upto 78.5 emu/g and an increase in magneto-crystalline anisotropic was observed with the increase in La 3+ substitution. In addition, for the first time we have reported the Mosssbauer study of BaLa x F 12− x O 19 nanohexaferrites in the present paper.

Nanocrystalline Al3+ and Cr3+ doped Ni–Co–Cu ferrites with the chemical composition Ni0.7Co0.2Cu0.1Al0.5xCr0.5xFe2-xO4 (x = 0.0, 0.1, 0.2) were prepared for demonstrating their structural, surface morphological and magnetic characteristics. The technique used for synthesizing the doped and undoped Ni–Co–Cu nanoferrites was sol-gel auto-combustion technique. The existence of single phase was confirmed with the help of X-ray diffractometry (XRD) which indicates the presence of spinel cubic structure for the synthesized specimens. The crystallite size (D) was determined from the highest intense (311) peak of the observed x-ray diffraction patterns by Debye-Scherrer formula and it was found in the dimensions of 44–55 nm. FESEM micrographs shows the existence of agglomerated and spherical magnetic nanoparticles with an average grain size of 63–78 nm. The prepared samples were examined with energy dispersive x-ray spectroscopy for the analysis of purity of synthesized samples and thus, from the EDX spectrum, only peaks of nickel, cobalt, copper, aluminium, chromium, iron and oxygen were observed which confirms the high purity of our results to a next level. The magnetic study was taken into consideration by vibrating sample magnetometer (VSM) and therefore, from the M − H curves data, various magnetic parameters were calculated. From the M − H loops measurements, the maximum of saturation magnetization (Ms) observed was 52.49 emu/g along with few hundreds of coercivity (Hc) indicating the ferromagnetic and soft behaviour of synthesized specimens. Therefore, in the present investigation, excellent values of saturation magnetization (28.11–52.49 emu/g) and coercivity (536.6–591.02 Oe) were obtained making these nanoferrites suitable for the high-density recording media and electromagnets application.

A series of the Y-type hexaferrites having chemical composition Sr2-xDyxCo2NiyFe12-yO22 (x = 0.0, 0.01, 0.02, 0.03, 0.04 and y = 0.0, 0.1, 0.2, 0.3, 0.4) were fabricated with doping of Dy3+ and Ni2+. XRD patterns confirm the formation of a single-phase hexagonal structure along with some impurity phases. FESEM and TEM analysis shows the formation of agglomerated magnetic nanoparticles. M − H loops obtained from VSM observations were used to study the magnetic parameters viz. saturation magnetization (Ms = 34.285–44.782 emu/g), remanence (Mr = 1.080–11.819 emu/g) and coercivity (Hc = 33.976–246.052 Oe), which were found to increase with an increase in Dy3+/Ni2+ substituents. The synthesized materials with excellent structural and magnetic properties are promising candidates for high-frequency applications.

In the present investigation, Ag+/Mn2+/Cr3+ doped Ni-Cu-Zn nanosized spinel ferrites with the chemical composition Ni0.4Cu0.3Zn0.3Ag0.4xMn0.3xCr0.3xFe2-xO4 (x ​= ​0.0, 0.05, 0.10, 0.15) were synthesized by sol-gel auto-combustion technique for reporting the microstructural, optical, magnetic and electrical properties of synthesized specimens. The identification of formation of single-phase structure of nanosized spinel ferrites was analyzed by X-ray diffractometry (XRD) and Field emitting scanning electron microscopy (FESEM). The crystallite size (D) decreases from 19 to 12 ​nm for lower concentration of dopants (x ​= ​0.0, 0.05, 0.10) whereas for the higher concentration (x ​= ​0.15), it starts increasing to 18 ​nm. As the crystallite size is less than 50 ​nm so, the synthesized Ni-Cu-Zn ferrites are suitable for obtaining noise to signal ratio in high density recording media. FESEM investigation depicted the presence of agglomerated and cubic magnetic nanoparticles. The FTIR investigation indicates the formation of characteristic absorption peak around 418.1–434.9 ​cm−1 and 571.2–592.5 ​cm−1 confirming our structural properties to a great extent. The magnetic characteristics are acutely investigated in regards with the structural and morphological traits. The saturation magnetization (Ms) and coercivity (Hc) are showing inverse relation to each other. With the increasing dopant concentration, Ms and nB was found to be decreasing from 66 emu/g to 54 emu/g and 2.82 μ B ​ to 2.33 μ B . Such high values of Ms and lower values of Hc illustrated the magnetic soft nature of Ni-Cu-Zn nanosized spinel ferrites suitable for multi-layer chip inductors (MLCIs) applications. In addition to this, the decreasing trend of dc resistivity with temperature indicating the semi-conducting nature of prepared samples because of thermal mobility of charge carriers.

Nanocrystalline cadmium and indium substituted barium M-type hexagonal ferrite-based nanomaterials were prepared via sol-gel auto-combustion technique for studying the electrical, dielectric and conductivity characteristics of prepared samples such as dc resistivity, dielectric constant ( e ’ ), dielectric loss (tan δ ) and ac conductivity ( σ a c ) with the usage of different characterizing techniques like keithley 2611 two probe system and impedance analyzer. The room temperature dc resistivity of synthesized samples increases for lower concentrations i.e. x = 0.1 of Cd2+/In3+ but for the higher concentrations i.e. x = 0.2, it starts decreasing consequently. The temperature dependent dc resistivity also showing a decreasing trend as a function of temperature which continuously indicating the semi-conducting behaviour of BaM hexagonal nanohexaferrites. The room temperature dielectric characteristics was investigated as a function of logarithmic frequency and it can be explained on the basis of Maxwell Wagner model and space chare polarization. From the dielectric measurements, the dielectric constant ( e ’ ) was found to be increasing with the increasing logarithmic frequency working as good energy storage material. The dielectric loss (tan δ ) was found to be decreasing for the undoped sample (x = 0.0) but for the undoped samples (x = 0.1–0.2), it starts increasing in a very minute manner. Therefore, such materials of high increasing dielectric constant with minute values of dielectric losses make it suitable for the high frequency, energy storage and microwave devices application.

BaHo x Fe 12− x O 19 ( x =0.1, 0.2, 0.3, 0.4) nanohexaferrites were successfully synthesized for the first time by sol–gel auto-combustion technique. X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDAX) were utilized to investigate the different structural parameters and elemental composition. Incorporation of Ho 3+ ions increased the dc resistivity while a decrease in the saturation magnetization ( M s ), 66.68–57.08 emu/g, followed by decrease in Curie temperature (766.83–758.15 K), exchange integral ( J ), and anisotropy was observed. The obtained values of M s were found to be very high as compared to the values reported in the bulk form. The dielectric constant ( e′ ) and dielectric loss tangent (tan δ ) were investigated as a function of frequency and the behavior is explained on the basis of Maxwell–Wagner model and Koop׳s theory. Additionally, a maiden attempt was made to explore the BaHo x Fe 12− x O 19 nanohexaferrites at ultra-high frequencies and observed ultra-low magnetic loss (0.004–0.01) and dielectric loss (0.004–0.06).

Mg–Gd–Mn nanoferrites with formulae Mg0.9Mn0.1GdyFe2−yO4, where y=0.05, 0.1, 0.2 and 0.3, have been synthesized by solution combustion technique. The dc resistivity was observed to decrease with the increase in temperature. Dielectric constant (e′) and loss tangent (tan δ) have been found to be increasing with an increase in temperature while with an increase in frequency both have been found to be decreasing. The ac electrical conductivity (σac) has been studied as a function of temperature at different frequencies and has been observed to be increasing with the increase in temperature. The Mossbauer spectroscopy has been carried out so as to authenticate our previously reported results on the super-exchange interactions.

Sol–gel synthesized BaGdxFe12−xO19, (x=0.0, 0.1, 0.2, 0.3) nanohexaferrites, have been explored for magnetic and microwave properties. X-ray diffraction studies revealed the hexagonal structure of the synthesized ferrites. The particle size was observed to be in the range 90–84 nm. The dc resistivity was found to be increasing with an increase in Gd3+ content and the variation of dc resistivity with temperature confirmed the semiconducting behavior of all nanohexaferrites. The observed values of saturation magnetization and coercivity, at room temperature, are 81.34 emu/g and 6020 Oe respectively which are very high as compared to the values ever reported till date. Additionally, we observed ultra-low magnetic loss (0.004–0.01) and dielectric loss (0.004–0.06) over the GHz frequency region. The obtained results make these nanohexaferrites a competent material for antenna applications up to C-band.

The Gd 3+ substituted Mg–Mn nanoferrites with generic formula Mg 0.9 Mn 0.1 Gd x Fe 2− x O 4 ( x = 0.05, 0.1, 0.2, 0.3) have been prepared for the first time by self-ignited solution combustion method. The X-ray analysis confirmed the formation of single phase cubic spinel structure. Gd 3+ substitution has resulted in an increase in the crystallite size (13.4–16.1 nm) and lattice parameter (8.35–8.38 A). The M – H and ZFC–FC study revealed that all nanoferrites are of superparamagnetic in nature. The saturation magnetization ( M s ) has been observed to decrease with the incorporation of Gd 3+ ions. The cation’s distribution has been estimated by using the magnetic characterization method. The magnetic properties such as initial permeability ( μ i ) and magnetic loss tangent (tan δ ) have been investigated as a function of frequency. The initial permeability has been observed to be almost constant with frequency and in each nanoferrite an onset of resonance is observed. In addition, very low values of ‘tan δ ’ were obtained.

Mg 0.9 Mn 0.1 Gd x Fe 2− x O 4 nanoferrites were processed for the first time by a solution combustion technique. X-ray diffraction studies revealed the spinel cubic structure of the synthesized ferrites. The particle size was observed to increase (13–16 nm) with an increase in Gd 3+ ion content. The cation distribution is inferred from the X-ray diffraction. It is observed from cation distribution that Gd 3+ ions preferred octahedral (B) sites. The DC resistivity was found to be increasing with an increase in Gd 3+ content. The dielectric constant e′ and loss tangent (tan δ ) was observed to decrease with the addition of Gd 3+ content as well as with the increase in frequency. The variations in DC resistivity as well as dielectric constant with the increasing substitution of Gd 3+ ions have been correlated to the cation distribution. The very high values of DC resistivity (~10 8 Ω cm) and low values of loss tangent (0.9–0.008) are the prime achievements of this work.

In the present work BaFe12O19 nano-hexaferrite had been synthesized by sol-gel method and then characterized for its structural, electric, dielectric and magnetic properties. X-ray diffraction studies confirmed the hexagonal structure of the prepared nanohexaferrite with no secondary phase and the particle size was found to be of the order of 49 nm. Further, the morphology of the sample has been studied by using transmission electron microscopy (TEM). A high value of the DC resistivity (5.5 × 10 6 Ω cm), has been obtained at room temperature. The dielectric properties such as dielectric constant (e'), dielectric loss tangent (tan δ) and ac electrical conductivity (σac) are investigated as a function of frequency. The dielectric constant and loss tangent are found to be decreasing with the increase in frequency while ac electrical conductivity is observed to be increasing with the increase in frequency. The dielectric properties have been explained on the basis of Maxwell-Wagner's two-layer model and hopping of the charge. The magnetic properties such as initial permeability (µi) and relative loss factor (RLF) have been investigated as a function of frequency in the range 75 kHz to 30 MHz .Fairly constant value of initial permeability and low values of RLF of the order of 10 -4 over a wide frequency range are the cardinal achievements of the present work. The room temperature M-H study shows that present nanohexaferrite has high value of coercivity (2151.3 Oe) and high saturation magnetization (32.5 emu/gm), which make present nanohexaferrite very suitable for magnetic applications. The M-T study shows that prepared nano-hexaferrite has high Tc (746 K). Copyright © 2014 VBRI press.