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We report the dopant- and size-dependent variations in high-frequency magnetic and electrical transport properties of Ho-substituted Li-Mn polycrystalline ferrites. Thermal stability and phase identification were confirmed by thermal gravimetric analysis and X-ray diffraction experiments. The overall average crystallite size decreased from 29.6 to 17.5 nm, whereas the bulk density increased from 3.47 to 4.29 g/cm 3 with increasing Ho content. Ferromagnetic resonance (FMR) measurements at the X-band revealed significant shifts in FMR linewidths and resonance positions as a function of composition. Both, FMR linewidth and porosity, were found to decrease with the systematic addition of Ho from 2538 to 2359 Oe and from 26% to 15.4%, respectively. The substitution of Ho 3+ for Fe 3+ reduced the net magnetization of the spinel lattice from 53 to 41 emu/g. Electrical measurements revealed that the resistivity is higher in samples with smaller grains possessing a greater number of thin insulating grain boundaries. The activation energy ∆ E required for hopping increases from 0.09 to 0.16 eV with Ho addition, which may be well explained by the increase in resistivity. The substitution of Ho 3+ for Fe 3+ causes a decrease in Curie temperature T c due to the damping of A-B exchange interactions. [ABSTRACT FROM AUTHOR]

A comprehensive study on structural, spectral, magnetic and dielectric properties of holmium substituted (Ho 3+ ) lithium ferrites; Li 1.2 Co 0.4 Ho x Fe 2−x O 4 (x = 0.00–0.15) synthesized via auto-citric combustion route has been carried out. The annealing temperature essential for complete decomposition of precipitates and spinel phase formation was found around 950 °C which was estimated from thermo-gravimetric analysis (TGA). The development of face centered cubic (FCC) spinel structure was confirmed from X-ray diffraction (XRD) analysis. However, the traces of an ortho phase (HoFeO 3 ) were appeared for x ≥ 0.06 indicating the solubility limit of Ho 3+ ions. The lattice constant ′ a′ increased from 8.351 to 8.360 Å upon Ho addition up to x = 0.06 and it decreased thereafter from 8.360 to 8.352 Å. This decrease in lattice constant was attributed to the secondary phase formation revealing segregation of Ho 3+ ions at grain boundaries. The porosity was found to decrease from 44 to 23% by the inclusion of Ho 3+ ions. Fourier transform infrared spectra (FTIR) exhibited tetrahedral ( v 1 ) and octahedral ( v 2 ) intrinsic vibrational bands at 627 cm −1 and 479 cm −1 respectively and these bands revealed a shift with increasing Ho concentration. The variations in force constants ( K o and K t ) were calculated and discussed with the tetrahedral (r A ) and octahedral (r B ) bond length trends. The dielectric parameters have been investigated as a function of composition and frequency. The systematic addition of Ho gradually increased the ac conductivity from 8.97 × 10 3 to 5.56 × 10 4 (Ω-cm) −1 up to x = 0.12 and it subsequently decreased for x = 0.15. The complex impedance examination (Cole-Cole plots) confirmed a grain-interior phenomenon, effectively contributing to the dielectric properties. The coercivity was enhanced while the saturation magnetization (Ms) was lessened by the incorporation of Ho 3+ ions. The maximum value of coercivity (706 Oe) was obtained for Li 1.2 Co 0.4 Ho 0.12 Fe 1.88 O 4 . The improved coercivity may suggest their utilization in perpendicular recording media applications. [ABSTRACT FROM AUTHOR]

We present the effects of size and oxygen defects on electrical and optical properties of nano crystalline bismuth ferrite (BiFeO 3 ) with rhombohedral symmetry synthesized by solution evaporation method. The effects of oxygen vacancies on the behavior of system have been studied by annealing all samples under two different environments, air and oxygen. Single phase crystal structure was confirmed by X-Ray diffraction (XRD). The crystalline size calculated by Scherrer's formula falls in the range of 11–21 nm for air and 20–29 nm in case of oxygen annealing atmosphere. The crystalline size was confirmed by Transmission electron microscope (TEM). Dielectric response reveals that both dielectric constant and dissipation factor (tanδ) decrease with increase of frequency without depicting any peak. Optical studies showed that the system possesses an indirect energy gap whose value increases with increasing particle size. There is an evidence for the presence of intra band states in this system arising from defect states. [ABSTRACT FROM AUTHOR]

The present study investigates the photocatalytic activity of NiCoPrFe 2 O 4 and Cd-NiCoPrFe 2 O 4 synthesized by the self-ignition sol-gel process. NiCoPrFe 2 O 4 @CNTs was prepared via ultrasonication approach. Methyl violet was used as a dye to examine the photodegradation activities of synthesized photocatalysts under visible light. The spinel crystalline structure is confirmed by XRD. The morphology of the as prepared samples was observed via scanning electron microscopy. NiCoPrFe 2 O 4 , Cd-NiCoPrFe 2 O 4 , and NiCoPrFe 2 O 4 @CNTs showed 55.46%, 78.29%, and 85.96% percentage degradation of methyl violet respectively. The photocatalytic performance of CNT based nanocomposite is found to be increased due to the enhanced charge separation property of CNT. • The sol-gel method was used for the preparation of NiCoPrFe2O4. • XRD and FTIR corroborate the structure and composition of elemental features. • SEM analysis confirms the morphology of the material. • NiCoPrFe2O4@CNT composite had shown excellent result is the photo-degradation of methyl violet. [ABSTRACT FROM AUTHOR]

Co2+ and Mn2+ co-doped lithium spinel ferrites with the chemical composition Li 0.5 Fe 2.5-0.5x Co x Mn x O 4 (x = 0.0–0.5) were fabricated by micro-emulsion method. The spinel structure with face centered the cubic phase was confirmed from the XRD study. The lattice constant was found to increase first from 8.369 to 8.374 Å and then decreased up to 8.367 Å, as the substitution level increased, attributed to the formation of the secondary phases. The crystallite size of nano ferrites was found in the range of 47 to 37 nm. Substitution of Co2+ and Mn2+ significantly enhanced the density of prepared ferrites. FTIR studies revealed the appearance of the characteristic vibration bands of Li 0.5 Fe 2.5 O 4 between 550 and 650 cm−1 which were appreciably influenced by the concentration of Co2+ and Mn2+. The force constants showed an indirect variation with the bond lengths of A- and B -sites. The dielectric properties such as dielectric constant (εʹ), complex dielectric constant (εʹʹ) and tangent loss (tanδ) were analyzed between 1 MHz and 3 GHz. By increasing the frequency, εʹ, εʹʹ, and tanδ were decreased and have shown a dispersive behavior at higher frequencies due to the effect of space-charge polarization. The obtained low values of dielectric loss may refer these materials for applications in transformer cores and high-frequency devices. • Growth of Li0.5Fe2.5-0.5xCoxMnxO4 (x = 0.0–0.5) ferrites by micro-emulsion method. • The lattice constant was found to increase first from 8.369 to 8.374 Å and then decreased. • FTIR studies revealed characteristic vibration bands of Li0.5Fe2.5O4 between 550 and 650 cm-1. • The dielectric properties were analyzed between 1 MHz and 3 GHz. [ABSTRACT FROM AUTHOR]

Ni 0.5 Sn 0.5 Co x Mn x Fe 2−2x O 4 ferrites with x = 0.0–0.8 have been prepared by the micro-emulsion method, using CTAB as a surfactant material. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR) and vibrational sample magnetometer (VSM) were used to investigate the effects of Co and Mn substitutions on cationic distribution, crystallite size, lattice constant, spectral, magnetic and dielectric properties. Lattice constant and crystallite size were found to increase from 7.4 to 9.25 Å and from 11.8 to 19.7 nm respectively with increasing substitution of Co and Mn ions. Saturation magnetization (M S ) gradually increased from 20.5 to 47.6 emu/g with increase in the value of x. However, Coercivity increased from 152.7 to 462.4 Oe up to x = 0.4 and then it decreased thereafter. The dielectric constant, complex dielectric constant and tan loss (tanδ) were observed to decrease with increase in frequency, depicting the semiconductor behavior of the ferrites. Dc resistivity was observed to decrease considerably upon addition of Co and Mn content. The outcome for the tunable magnetic properties and achieved modification of the synthesized nanocrystallites may be chosen for tremendous applications; such as miniaturized memory devices that are based on the energy storage principles and capacitive components. [ABSTRACT FROM AUTHOR]

A series of holmium (Ho) doped nanocrystalline Ni 0.7 Zn 0.3 Ho 2x Fe 2–2x O 4 ; 0.0≤x≤0.07 ferrite was synthesized using the conventional ceramic technique. The cubic spinel structure was confirmed by powder X-ray diffraction (XRD). The lattice parameter increases with increase in Ho content due to large ionic radius of Ho 3+ (0.901 Å) as compared to Fe 3+ (0.67 Å). Room temperature DC electrical resistivity and activation energy both increase with the increase of holmium contents. The saturation magnetization (M s ) decreased gradually from 78.92 to 54.17 emu/g due to holmium ions substitution in Ni-Zn ferrites. This decrease in M s is explained on the basis of redistribution of cations amongst the sites and weakening the A-B exchange interactions. An increase in electrical resistivity made this material suitable for its use in high frequency device applications. [ABSTRACT FROM AUTHOR]