A study of structural, ferroelectric, ferromagnetic, dielectric properties of NiFe2O4–BaTiO3 multiferroic composites

The mixed spinel-perovskite multiferroic composites of xNiFe₂O₄-(1 ? x)BaTiO₃ (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) have been prepared by sol–gel method. The structure and morphology of the composites were examined by means of X-ray diffraction and transmission electron microscope. High-resolution transmission electron microscope image indicates a clear view of ferrite and ferroelectric phase. Moreover, we observed a fine interface between the two phases, where the coupling effect of ferrite and ferroelectric phase happened. The composites show excellent ferromagnetic and ferroelectric properties. The saturation magnetization (M_s) reaches to 24.139 emu/g for x = 0.6 at room temperature, the magnetization is about 2.37 emu/g for x = 0.6 when the temperature decreases to 90 k, and the polarization reaches to 3.75 μC/cm² for x = 0.1. Frequency dependent variations of dielectric constant and loss tangent for xNiFe₂O₄-(1 ? x)BaTiO₃ were studied in detail.     

Structural and electrical properties of La-modified BiFeO3–BaTiO3 composites

In the present investigation, La-modified solid solutions of BiFeO₃ (BFO) and BaTiO₃ (BT) in different molar ratios [i.e., (Bi_0.5?x La _x Ba_0.5)(Fe_0.5Ti_0.5)O₃, with x = 0.0, 0.05, 0.10 and 0.15)] have been synthesized using a solid-state reaction route. Structural and electrical properties of single phase (with minor secondary phase) of BFO–BT system have been studied in details to understand their ferroelectric and other properties. Preliminary X-ray diffraction analysis confirms the formation of a new system, which is different from that of its parent compounds. Substitution of a small amount BaTiO₃ into BiFeO₃ enhances dielectric and ferroelectric responses and reduces electrical leakage or tangent loss. The ac conductivity obeys Jonscher’s universal power law. The electrical behavior of the samples was investigated by impedance spectroscopy in a wide temperature range (25–525 °C) at different frequency (1 kHz–1 MHz). The impedance spectroscopy of the materials also confirms the origin of the relaxation mechanism in the system.     

Dielectric and multiferroic properties of 0.75BiFeO3–0.25BaTiO3 solid solution

Solid solution 0.75BiFeO₃–0.25BaTiO₃ (BFO–25 % BT) was prepared by solid state reaction method. Powder X-ray diffraction showed the morphotropic phase boundary (MPB) with the coexistence of both rhombohedral and cubic phases due to splitting in the line at 2θ = 39.7°. Scanning electron micrographs indicated that the ceramic has compact and uniform microstructure with average grain size <3 μm. The polarization vs applied electric field analysis showed an unsaturated hysteresis loop with the remnant polarization 12.95 μC/cm² at 22 kV/cm for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The calculations of diffuse parameter i.e. slope γ = 1.63 suggested a high degree of diffusion in BFO–BT lattice. The room temperature magnetic measurements confirmed the weak ferromagnetism of magnetization ~0.1 emu/gm at an applied magnetic field of H = 5 kOe for 0.75BiFeO₃–0.25BaTiO₃ ceramic. The high temperature magnetic and dielectric analysis suggested a coupling between ferroelectric and magnetic parameters near the antiferromagnetic–paramagnetic transition T_c ~ 310 °C, which was responsible for the broad frequency dependent dielectric maxima. The impedance spectroscopy and complex modulus analysis confirmed the conventional relaxor, NTCR (negative temperature coefficient of resistance), giant ferroelectricity and polydispersive non-Debye type dielectric relaxation behaviour for 0.75BiFeO₃–0.25BaTiO₃ ceramic at 170 °C on 1 kHz with activation energy 2.33 eV. The modulus analysis also confirmed the possibility of hopping mechanism for electrical transport process in material.     

Investigation of optical,dielectric, and multiferroic properties of (1 − x) Bi0.9La0.1FeO3–(x) BaTiO3 composites

Journal of Materials Science: Materials in Electronics - In the present work, we synthesized composites (1???x) Bi0.9La0.1FeO3-(x) BaTiO3 with x?=?0.05, 0.10, and 0.15...     

Preparation and characterization of BaTiO3–natural muscovite composites

Journal of Materials Science: Materials in Electronics - Natural muscovite (nM) exhibiting magnetic vortex states are ball milled into fine powder and mixed in different relative ratios (weight %)...     

Preparation and magnetic properties of Ni–Zr doped barium strontium hexaferrite

M-type Hexaferrites B_0.5Sr_0.5Fe_12−2x Ni _x Zr _x O₁₉ were synthesized and investigated. The XRD patterns show single phase of the magnetoplumbite barium strontium ferrite and no other phases were present. The samples exhibit well defined crystallization; all of them are hexagonal platelet grains. As the substitution level increased from x = 0.2 to 0.8 mol%, the grains are agglomerated and the average diameter increased. This suggests that Ni–Zr substitution increases the grain size, as observed in the FE-SEM micrographs. The results of magnetic measurement revealed that M_s of barium strontium hexaferrite increased when the value of x increased from 0 to 0.4 mol% and then decreased with the increasing Ni–Zr content. The H_c decreases remarkably with increasing Ni and Zr ions content. Hard magnetic material is converted into soft magnetic material when the substitution level is increased from 0.2 to 0.8 mol%. In particular, Ba_0.5Sr_0.5Fe_12−2x Ni _x Zr _x O₁₉ with x = 0.2, 0.4, 0.6, 0.8 mol% has suitable magnetic characteristics with particle size small enough for high-density magnetic recording applications.     

Investigation of microstructure and mechanical properties of steel fibre–cast iron composites

Abstract

The aim of the present experimental study was to investigate improvement of the toughness and strength of grey cast iron by reinforcing with steel fibres. The carbon content of the steel fibres was chosen to be sufficiently low that graphite flakes behaving as cracks were removed by carbon diffusion from the cast iron to the steel fibres during the solidification and cooling stages. To produce a graphite free matrix, steel fibres with optimum carbon content were used and the reinforced composite structure was cast under controlled casting conditions and fibre orientation. Three point bend test specimens were manufactured from steel fibre reinforced and unreinforced flake graphite cast iron and then normalising heat treatments were applied to the specimens at temperatures of 800 and 850°C. The fracture toughness and strength properties of the steel fibre reinforced material were found to be much better than those of unreinforced cast iron. The microstructures of the composite at the fibre–matrix transition zone were examined.     

Influence of Mn doping on structural,electrical and magnetic properties of (0.90)BiFeO3–(0.10)BaTiO3 composite

Structural, electrical and magnetic properties of chemically synthesized polycrystalline Mn doped (0.90)BiFeO₃–(0.10)BaTiO₃ composites [(0.90)BiFe_1?xMn_xO₃–(0.10)BaTiO₃ (x = 0.0, 0.03, 0.05 and 0.10)] were studied. The dielectric constant was observed to decrease when frequency was increased from 20 Hz to 1 MHz and increased with the increase in temperature from 313 to 773 K. An interesting correlation between the antiferromagnetic Neel temperature (T_N) of bismuth ferrite and temperature dependent dielectric constant was observed. The calculated values of activation energies were in the order of 0.25–0.74 eV (<1.0 eV) and decreases with an increase of Mn concentration. The variation of a.c. conductivity obeyed the Jonscher’s power law (σ _ac  ∝ ω ^s ). The observed value of exponent‘s’ were in the range 0.09 < ‘s’ < 0.78 (<1.0) for all the sample at temperature ranging from 473 to 598 K. There was a systematic increase in the value of spontaneous magnetization on increasing Mn concentration.     

Butterfly-shaped multiferroic BiFeO3@BaTiO3 core–shell nanotubes: the interesting structural, multiferroic, and optical properties

Highly pure butterfly-shaped BiFeO₃@BaTiO₃ nanotubes have been synthesized through a sol–gel method. An obvious ferromagnetic behavior was obtained at room temperature, with a large coercive field (5,403 Oe) and high Mr/Ms value (0.52). The dielectric permittivity of BiFeO₃@BaTiO₃ nanotubes was found to be 1919, which is much higher than that of pure BFO nanostructure. The dielectric loss of BiFeO₃@BaTiO₃ nanotubes is low in the frequency range from 10 Hz to 1 MHz. The maximum magnetoelectric coefficient of BiFeO₃@BaTiO₃ nanotube is 0.272 μV/cm Oe. Moreover, the BiFeO₃@BaTiO₃ nanotubes have exhibited a better ferroelectric property with a large band gap of 3.2 eV which demonstrates the core–shell nanostructure.     

Electrical and magnetic properties of BaTiO3−(Ni0.3Zn0.7)Fe2.1O4 composites

Ceramic composites consisting of ferroelectric and ferrite ( were synthesized by the mixed oxide route. The phase assemblage, electrical and magnetic properties of the samples were investigated. The results indicates that the phase is compatible with ( phase, and dense diphasic composite ceramics were obtained. Electrical resistivity of composites varies with increasing amounts of ( phase, and shows a percolation-like drop. Magnetic hysteresis loops were observed in the composites.     

Enhanced electric field tunable magnetic properties of lead-free Na0.5Bi0.5TiO3–MnFe2O4 multiferroic composites

Strong magnetoelectric (ME) interaction was exhibited at both dc and microwave frequencies in a lead-free multiferroic particulate composites of Na_0.5Bi_0.5TiO₃ (NBT) and MnFe₂O₄ (MFO) multiferroic, which were prepared by sol–gel route. The room temperature permeability measurements were carried out in the frequency range of 1 MHz–1 GHz. A systematic study of structural, magnetic and ME properties were undertaken. The room temperature ferromagnetic resonance (FMR) was studied. Strong ME coupling is demonstrated in 70NBT–30MFO composite by an electrostatically tunable FMR field shift up to 428 Oe (at E = 4 kV/cm), which increases to a large value of 640 Oe at E = 8 kV/cm. Furthermore, these lead-free multiferroic composites exhibiting electrostatically induced magnetic resonance field at microwave frequencies provide great opportunities for electric field tunable microwave devices.     

Mn0.7Zn0.3Fe2O4 + BaTiO3 composites: structural,morphological, magnetic,M–E effect and dielectric properties

Here in the present investigation, constituent phases of (1 ? x)Mn_0.7Zn_0.3Fe₂O₄(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 (α_ME?=?20.45 mVcm^?1 Oe^?1). The improved magnetoelectric properties make MZFO–BTO composite applicable for electronic devices.

     

Structural and magnetic properties of Ce3+doped Mg-Co ferrite prepared by sol–gel method

Journal of Materials Science: Materials in Electronics - Ce3+-doped Mg-Co ferrite powder can be prepared by sol–gel spontaneous combustion method. The chemical formula for...     

The investigation of structural and magnetic properties of Er2−xCoxO3 nano-oxides

Journal of Materials Science: Materials in Electronics - The sol–gel technique was used to synthesize Er2?xCoxO3 (0.0?≤?x?≤?0.30) mixed oxides to...