[en] The nanocrystalline MgCuZn ferrites with particle size (∼30 nm) have been synthesized by microwave-hydrothermal (M-H) method at 160 deg. C/45 min. The powders were densified at 750-900 deg. C/30 min using microwave sintering method. The sintered samples were characterized using X-ray diffraction and scanning electron microscope. The grain sizes of the sintered samples are in the range of 60-80 nm. The ultrasonic velocities have been measured on MgCuZn ferrites using the pulse transmission method at 1 MHz. The ultrasonic velocity is found to decrease with an increase of temperature. A small anomaly is observed around the Curie temperature, 520 K. The anomaly observed in the thermal variation of longitudinal velocity and attenuation is explained with the help of magneto-crystalline anisotropy constant.

[en] Highlights: ► The study of elastic properties of nanocrystalline MnZn ferrites synthesized by microwave hydrothermal method was reported for first time. ► The temperature and magnetic field dependence of Young's modulus and internal friction have been measured for the first time. ► To understand the interaction of domain wall with ultrasonic velocity a detailed study has been carried out for the first time. -- Abstract: Microwave-hydrothermal (M-H) method has been successfully used for synthesis of nanocrystalline Mn–Zn ferrites which are used for high frequency applications. The nanopowders were characterized using XRD and TEM. The particle size of the samples varies from ∼20 nm to 25 nm. The powders were densified at 900 °C/30 min using microwave sintering method. The sintered ferrite samples were characterized using XRD, X-ray photoelectron spectroscopy (XPS), SEM and energy dispersive X-ray spectroscopy (EDS). The elastic behaviour and internal friction studies were carried out using composite piezoelectric oscillator method in the temperature range of 300–600 K. It was found that the anomalous behaviour observed in the temperature dependence of Young's modulus and internal friction disappears with the application of a magnetic field equal to the saturation field (900 mT) of the specimen under investigation. The observed anomalous behaviour in the vicinity of the Curie temperature was understood with the help of Landau's theory.

[en] The nanocrystalline Ni_0.53Cu_0.12Zn_0.35Fe_1.88O₄ and BaTiO₃ powders were prepared using Microwave-Hydrothermal (M-H) method at 160 ^oC/45 min. The as synthesized powders were characterized using the X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The size of the powders that were synthesized using M-H system was found to be ∼30 and ∼50 nm for ferrite phase and ferroelectric phases, respectively. The powders were densified using microwave sintering method at 900 ^oC/30 min. The ferrite and ferroelectric phases were observed from XRD and morphology of the composites was observed with the Scanning Electron Microscope (SEM).The magnetic hysteresis loops were recorded using the Vibrating Sample Magnetometer (VSM).The frequency dependence of real (μ') and imaginary (μ'') parts of permeability was measured in the range of 1 MHz-1.8 GHz. The permeability decreases with an increase of BaTiO₃ content at 1 MHz. The transition temperature (T_C) of ferrite was found to be 245 ^oC. The T_C of composite materials decreases with an increase in BaTiO₃ content.

[en] Ni_0.53Cu_0.12Zn_0.35Fe₂O₄/SiO₂ nanocomposites with different weight percentages of NiCuZn ferrite dispersed in silica matrix were prepared by microwave-hydrothermal method using tetraethylorthosilicate as a precursor of silica, and metal nitrates as precursors of NiCuZn ferrite. The structure and morphology of the composites were studied using X-ray diffraction and scanning electron microscopy. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer in the range of 400-1500 cm^-1. The bands in the range of 580-880 cm^-1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe₂O₄ clusters and silica matrix. The effects of silica content and sintering temperature on the magnetic properties of Ni_0.53Cu_0.12Zn_0.35Fe₂O₄/SiO₂ nanocomposites have been studied using electron spin resonance and vibrating sample magnetometer. - Highlights: → No literature data is available on the microwave-hydtothermal synthesis method of NiCuZn ferrite/SiO₂ nanocomposites so far. → Using the microwave-hydrothermall synthesis method the magnetic properties of NiCuZn ferrite/SiO₂ nanocomposites are enhanced. → Using this method, the reaction time can be very low. → Low temperature crystallization can be achieved using nanopowders and grain sizes of the composites can be controlled using microwave sintering method.

[en] Nanosized BaTiO₃ powder was synthesized at 160 deg. C/45 min using the Microwave Hydrothermal (M-H) system. The nanopowder was characterized using X-ray diffraction, transmission electron microscopy, infrared spectroscopy and differential scanning calorimetry. The as-synthesized powder was microwave sintered at 950, 1050 and 1150 deg. C/30 min in air and for the comparison the nanopowder was also conventionally sintered at 1250 deg. C/3 h in air

[en] Microwave-Hydrothermal (M-H) method has been successfully used for the synthesis of nanocrystalline Mn-Zn ferrites which are used for high-frequency applications. As synthesized powders were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The nanopowders were annealed at 600 ^oC/20 min using the microwave sintering method. The frequency dependence of dielectric constant (ε') was measured in the range of 10 Hz-1.3 GHz and initial permeability (μ_i) was measured in the range of 10 Hz-1 MHz. The total power loss (P_t) was measured on the annealed samples at 100 kHz and 200 mT condition. Conductor-embedded-ferrite transformers were fabricated and output power (P_o), efficiency (η) and temperature rise (ΔT) were measured at sinusoidal voltage of 25 V at 1 MHz. The transformer efficiency (η) was found to be high and surface rise of temperature (ΔT) is very low.

[en] The structural analysis and magnetic investigation Mn_1_−_xZn_xFe_2O_4 with stoichiometry (x=0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were synthesized by solution combustion method using mixture of fuel this is first of its kind. As synthesized Mn–Zn nanoferrites were characterized by X-ray Diffractometer (XRD), Transmission electron microscopy (TEM) at room temperature. The magnetic domain relaxation was investigated by inductance spectroscopy (IS) and the observed magnetic domain relaxation frequency (f_r) was increased with the increase in grain size. The Room temperature magnetic properties were studied using vibrating sample magnetometer (VSM). It was observed that the real and imaginary part of permeability (μ′ and μ″), saturation magnetization (M_s), remanance magnetization (M_r) and magneton number (M_r/M_s) were decreases gradually with increasing Zn"2"+ concentration. The decrease in the saturation magnetization may be explained as, the Zn"2"+ concentration increases the relative number of ferric ions on the A sites diminishes and this reduces the A–B interaction. Hence synthesized materials are good for high frequency applications. - Highlights: • Mixture of fuels used for synthesis. • Preferred existence of Fe"3"+ oxidation states. • Reduction in magnetic interaction between Fe ions due to Zn"2"+ dilutions. • These materials are useful for high frequency applications.

[en] To investigate the modification effect of the modifier ZnO on boro-tellurite glass, a series of glasses with compositions 50B₂O₃-(50-x)ZnO-xTeO₂ have been prepared by conventional melt quenching technique. Amorphous nature of the samples was confirmed through X-ray diffraction technique. Optical absorption and IR structural studies are carried out on the glass system. The optical absorption studies revealed that the cutoff wavelength increases while optical band gap (E_opt) and Urbach energy decreases with an increase of ZnO content. Refractive index evaluated from E_opt was found to increase with an increase of ZnO content. The compositional dependence of different physical parameters such as density, molar volume, oxygen packing density, optical basicity, have been analyzed and discussed. The IR studies showed that the structure of glass consists of TeO₄, TeO₃/TeO₃₊₁, BO₃, BO₄ and ZnO₄ units. -- Research highlights: → Novel boro-zinc tellurite ternary glasses that can compete with boro-tellurite and zinc tellurite glasses are successfully prepared. → Boro-zinc tellurite ternary glasses are of higher refractive index compared with zinc tellurite glasses. → Optical, physical and structural properties of the novel ternary glass system are explained.→ At 30 mol% of ZnO, TeO₄ is replaced by ZnO₄ indicating the presence of ZnO₄ network.

[en] Nanocrystalline Mn_0.4 Zn_0.6 Sm_xGd_yFe_2-(x+y)O₄ (x = y = 0.01, 0.02, 0.03, 0.04 and 0.05) were synthesized by combustion route. The detailed structural studies were carried out through X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM). The results confirms the formation of mixed spine phase with cubic structure due to the distortion created with co-dopants substitution at Fe site in Mn–Zn ferrite lattice. Further, the crystallite size increases with an increase of Sm³⁺–Gd³⁺ ions concentration while lattice parameter and lattice strain decreases. Furthermore, the effect of Sm–Gd co-doping in Mn–Zn ferrite on the room temperature electrical (dielectric studies) studies were carried out in the wide frequency range 1 GHz–5 GHz. The magnetic studies were carried out using vibrating sample magnetometer (VSM) under applied magnetic field of 1.5T and also room temperature electron paramagnetic resonance (EPR) spectra's were recorded. From the results of dielectric studies, it shows that the real and imaginary part of permittivities are increasing with variation of Gd³⁺ and Sm³⁺ concentration. The magnetic studies reveal the decrease of remnant, saturation magnetization and coercivity with increasing of Sm³⁺–Gd³⁺ ion concentration. The g-value, peak-to-peak line width and spin concentration evaluated from EPR spectra correlated with cations occupancy. The electromagnetic properties clearly indicate that these materials are the good candidates which are useful at L and C band frequency. - Highlights: • Phase formed at low temperature. • No further calcination was required. • Good magnetic properties and magnetically soft. • Moderate dielectric constant.

[en] Ni_0_._4Zn_0_._2Mn_0_._4Fe_2O_4 nanopowders were prepared by sol-gel auto-combustion method, densified at different temperatures 400–700 °C/4 h using conventional sintering method. The grain sizes of all the samples vary between 18 nm and 30 nm. The hysteresis loops show high saturation magnetization and low coercivity, indicating magnetically soft behaviour of the material. The real and imaginary parts of permittivity is almost constant upto 1 GHz and increases with further increase of frequency. The permeability is ruled by Snoek’s law, the values of μ′ increases with increase of temperature and the resonance frequency increases with an increase of temperature. The reflection coefficient is however increasing with sintering temperature and the maximum loss is observed in the range of 100 MHz–1 GHz. Sample sintered at 700 °C has shown maximum reflection loss and this loss occurs due to absorption, destructive interference and multiple internal reflections in the sample. Quality factor is constant upto 380 MHz and increases with frequency for all the samples sintered at different temperatures. The T_C for all the samples is above ~230 °C. The room temperature EPR spectra confirm the oxidation state of Fe"3"+. The g-factor is in the range of ~2. - Highlights: • The highest reflection loss of –46 dB is achieved by 700 °C sample. • Quality factor is constant upto 380 MHz for all the samples. • The Curie temperature (T_C) for all the samples is above ~230 °C. • The room temperature EPR spectra confirm the oxidation state of Fe"3"+.