Structural and magnetic properties of NiFe2−xBixO4 (x = 0, 0.1, 0.15) nanoparticles prepared via sol-gel method

NiFe_2−xBi_xO₄ (x = 0, 0.1, 0.15) nanopowders were synthesized via sol-gel method. The precursor gels were calcined at 773 K in air for 1 h to obtain the pure nanostructured NiFe_2−xBi_xO₄ spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe_2−xBi_xO₄ have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy, transmission electron microscopy and alternating gradient force magnetometry. Mössbauer spectroscopic measurements revealed that Bi³⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite, i.e., the crystal-chemical formula of the as-prepared nanoparticles may be written as: (Fe)[NiFe_1−xBi_x]O₄ (x = 0, 0.1, 0.15), where parentheses and square brackets enclose cations on sites of tetrahedral and octahedral coordination, respectively. Selective area electron diffraction studies provided evidence that the samples of the NiFe_2−xBi_xO₄ series, independently of x, exhibit the cubic spinel structure. The values of the saturation magnetization and the coercive field of NiFe_2−xBi_xO₄ nanoparticles were found to decrease with increasing degree of bismuth substitution.     

Nanocrystalline/Nanosized Ni1−γFe2+γO4 Ferrite Obtained by Contamination with Fe During Milling of NiO–Fe2O3 Mixture. Structural and Magnetic Characterization

The nanocrystalline nickel ferrite (NiFe₂O₄) was synthesized by reactive milling starting from equimolar mixture of oxides. The iron contamination during milling leads to a solid state reaction between Fe and NiFe₂O₄ spinel. This reaction starts for a milling time longer than 30 h. A mixed nickel–iron ferrite (Ni_1?γFe_2+γO₄) and elemental Ni are obtained. The evolution of the nickel–iron mixed ferrite during milling and its properties were investigated using X‐ray diffraction, Fourier Transform Infrared Spectroscopy (FTIR), Laser Particles Size Analyzer and magnetic measurements. Annealing treatment (350°C/4 h in vacuum) is favorable to the reaction between phases. Replacement of Ni²⁺ cations by iron cations provided by contamination leads to the increase of lattice parameter value of the spinel structure. The magnetization of the nickel–iron mixed ferrite newly formed is larger than the nickel ferrite magnetization (13.6 μ_B/f.u. and 6.22 μ_B/f.u., respectively), due to the magnetic moment of Fe²⁺ cation which is double as compared to the Ni²⁺ cation. Magnetization of the milled samples decreases during milling due to the structural changes induced by milling in the nickel–iron mixed ferrite. The annealing induces a reordering of the cations which leads to a larger magnetization.     

Magnetic behavior of nickel–bismuth ferrite synthesized by a combined sol–gel/thermal method

The bulk NiFe_2?xBi_xO₄ ferrites with various Bi³⁺ concentration (x=0, 0.1, 0.15) were synthesized via sol–gel procedure, starting from nickel, bismuth and iron nitrate powders, followed by the conventional thermal treatment. The structural and magnetic properties of the as-prepared ferrites were studied by means of X-ray diffraction, alternating gradient force magnetometry and Faraday balance. The anisotropy constant was determined by the law of approach to saturation (LAS) model. An increasing Bi³⁺ concentration in NiFe_2?xBi_xO₄ leads to a decrease in the saturation magnetization, Néel temperature and the anisotropy constant of the material.     

Magnetoelectric coupling in multiferroic BiFeO3 by co-doping with strontium and nickel

We report the effects of the Sr²⁺ and Ni²⁺ co-doping of BiFeO₃ on the crystal structure and multiferroic properties of Bi_1?xSr_xFe_1-yNi_yO₃ (x?=?0.05, 0.0?≤?y?≤?0.10, and Δy?=?0.05) that is synthesized using assisted high-energy ball milling. The mixtures of Bi₂O₃, Fe₂O₃, SrO and NiO were milled for 5?h, pressed at 900?MPa, and sintered at 800?°C in order to obtain cylindrical test pieces. X-ray diffraction and Rietveld refinement elucidated the effects of Sr²⁺ and Ni²⁺ on the crystal structure. Co-doping with SrNi in suitable proportions stabilizes rhombohedral BiFeO₃. High contents of Ni²⁺ promote the precipitation of secondary phases in the forms of NiFe₂O₄ and Bi₂₅FeO₄₀. The magnetic behavior was examined by means of vibrating sample magnetometry. The results showed a change in the magnetic order from antiferromagnetic for the undoped sample to the ferromagnetic order for the co-doped samples. This change is attributed to the modulations in the magnetic moment due to crystal structure distortions. All samples show high relative permittivity values, which were enhanced by doping with Sr²⁺. Ni²⁺ cations increase the dielectric dissipation factor; this enhancement is related to their interactions with cations of a different oxidation state, such as Fe³⁺, Fe²⁺, Ni²⁺, Bi³⁺ and Sr²⁺ in the crystal structure of BiFeO₃. The magnetoelectric coupling that was evaluated using magnetodielectric measurements was above 4% at 1?kHz for the higher applied magnetic field of 18?kOe.     

Synthesis and analysis of structural,compositional, morphological,magnetic, electrical and surface charge properties of Zn-doped nickel ferrite nanoparticles

Zn-doped nickel ferrite nanoparticles (Zn_xNi_(1-x)Fe₂O₄) were synthesized using the co-precipitation technique. The structural and compositional studies of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles revealed their face-centred cubic spinel structure and an appropriate amount of Zn doping in nickel ferrite nanoparticles, respectively. The morphological analysis had been carried out to obtain the particle size of the synthesized nanoparticles. The magnetic studies revealed the superparamagnetic nature of the Zn_xNi_(1-x)Fe₂O₄ nanoparticles, and the maximum magnetization of 30 emu/g for the Zn_0.2N_0.8Fe₂O₄ sample. The M ? H curves were fitted with the Langevin function to obtain the magnetic particle diameter of Zn_xNi_(1-x)Fe₂O₄ nanoparticles. The electrical conduction in Zn_xNi_(1-x)Fe₂O₄ nanoparticles was explained through the Verway hopping mechanism. The Zn_0.2N_0.8Fe₂O₄ nanoparticle exhibited a higher electrical conductivity of 42 μS/cm and surface charge of ?29/7 mV due to the enhanced hopping of Fe³⁺ ions in the octahedral sites. Owing to this nature, they were identified as the suitable candidates in the applications such as thermoelectrics, hyperthermia, magnetic coating and for the preparation of conducting ferrofluids.     

Temperature-induced strain mediated magnetization changes in NiFe2O4/BaTiO3 heterostructure

Herein, we report the temperature-induced magnetization changes of NiFe₂O₄ thin film, which is coated over a ferroelectric BaTiO₃ ceramic substrate. The solid-state reaction method was adopted for the preparation of ferroelectric BaTiO₃ (BT) substrate, whereas NiFe₂O₄ (NFO) film was deposited by spin-coating method. Rietveld refinement revealed that BT substrate has a tetragonal (P4mm) crystal system along with a minor orthorhombic phase (Amm2) at room temperature. The GIXRD analysis confirms the phase purity of NFO/BT heterostructure. Polarization hysteresis with respect to electric field (P-E loop) and the temperature-dependent dielectric measurement of BT substrate demonstrate its typical ferroelectric and phase transition behavior, respectively. Magnetization hysteresis loops were recorded for the NFO/BT heterostructure at 150, 240 and 300?K. A significant increase in the remnant magnetization (M_R) and coercive field (H_C) of NFO film are noticed while cooling the heterostructure below 300?K. Variation in the magnetization of NFO film corresponds to the change in the structural phase transition (Amm2 at 240?K and R3c at 150?K) of BT while cooling below RT. The interfacial strain mediated coupling is the primary mechanism attributed to the temperature-induced changes in the magnetization of NFO/BT heterostructure.     

Improvement in dielectric,ferroelectric and ferromagnetic characteristics of Ba0.9Sr0.1Zr0.1Ti0.9O3-NiFe2O4 composites

Multiferroic composites with the composition (1-x)Ba_0.9Sr_0.1Zr_0.1Ti_0.9O₃-(x)NiFe₂O₄ (x=0.0, 0.05, 0.10, 0.20 and 0.30) were prepared by mechano-chemical activation technique. Rietveld refined X-ray diffraction pattern shows the formation of individual perovskite (BSZT) and inverse spinel (NFO) phases for all the four composite samples. Microstructural investigation reveals that the inhomogeneity in grains increases with addition of NFO as compared to bare BSZT sample. Dielectric studies show that all the samples exhibit a well-defined ferroelectric to paraelectric transition peak. Further, the diffuseness of the samples increases as NFO content increases. Ferroelectric properties were found to be superior for (1-x)BSZT-(x)NFO sample with x=0.05 and decreases on further increase in NFO content. Dielectric breakdown strength also shows the similar trend as ferroelectricity and shows a maximum for x=0.05 ferrite (NFO) fraction. Magnetic measurement of BSZT-NFO composite samples shows a gradual increase in saturation magnetization and coercive field (H_c) with increasing NFO content.     

Effectiveness of Ni incorporation in iron oxide crystal structure towards thermochemical CO2 splitting reaction

In this study, Ni-doped iron oxide (Ni_xFe_3−xO₄) materials were synthesized via the 1,2-epoxypropane assisted sol-gel method by varying the molar concentration of Ni from x=0.2 to 1. Sol-gel derived Ni_xFe_3−xO₄ gels were dried and the dried powder was further calcined upto 600 °C in air for 90 min. Obtained calcined Ni_xFe_3−xO₄ powders were further analyzed to determine the phase composition, crystallite size, specific surface area, pore volume, and morphology via powder X-ray diffraction (PXRD), BET surface area analysis (BET), as well as scanning and transmission electron microscopy (SEM and TEM). The obtained results in the synthesis and characterization section indicate formation of Ni_xFe_3−xO₄ nanoparticles with high specific surface area. Thermal reduction and re-oxidation of the sol-gel synthesized Ni_xFe_3−xO₄ materials were determined by using the high temperature thermogravimetry. Obtained results indicate that the amount of O₂ released during the thermal reduction step (at 1400 °C) and quantity of CO produced during the CO₂ splitting step (at 1000 °C) increases as the concentration of Ni inside the iron oxide crystal structure increases. The highest amounts of O₂ released (221.88 μmol/g) and CO produced (375.01 μmol/g) in case of NiFe₂O₄ (NF10 material).     

Effects of Bi2O3 and Li2OB2O3Bi2O3SiO2 glass on electromagnetic properties of NiCuZn/BaTiO3 composite material at low sintering temperature

Bi₂O₃ and Li₂OB₂O₃Bi₂O₃SiO₂ (LBBS) glass were introduced into Ni_0.15Cu_0.24Zn_0.61Fe₂O₄BaTiO₃ ((NCZF-BTO) composite materials as sintering aids and sintered at 920?°C. Effects of Bi₂O₃ and LBBS glass on phases, microstructures, magnetic and dielectric properties of these composites were comparatively studied. In contrast to undoped composites, the addition of Bi₂O₃ or LBBS glass to samples enhances performance. Hence, when Bi₂O₃ content reached 1.5?wt%, saturation magnetization (4πM_s) increased from 3825.4 to 4912.5 Gs, static permeability (μ₀) increased from 53.2 to 197, and dielectric constant (ε′) increased from 18.3 to 23.4. When LBBS glass content reached 1.5?wt%, 4πM_s increased to 4145.6 Gs, μ₀ increased to 79.3, ε′ increased to 25.4. However, both coercivity (H_c) and dielectric loss (tan?δ) were reduced. In short, Bi₂O₃ promoted magnetic properties, whereas LBBS glass promotes dielectric properties more effectively.     

Spinel ferrites NiFe2O4 NCs enhanced Mössbauer spectra,magnetization and Faraday rotation of diamagnetic tellurite glasses

Glass containing magnetic nanocrystals are attractive for obtaining high magnetic and magneto-optical properties. In this study, for the first time, 10 nm cubic NiFe₂O₄ (NFO) nanocrystals doped heavy metal oxide glasses were fabricated and the influence of NFO to glass structure, chemical bonds, Mössbauer spectra, magnetization and Faraday rotation was studied. X-ray diffraction, Raman and X-ray photoelectron spectra revealed the existence of multi-valence states of Fe/Ni ions, oxygen vacancies in cubic lattice and modifications on glass structure, which in turn adjusted the polarizability, oxygen packing density, Mössbauer spectra, magnetic property and magneto-optical behaviors. Through Mössbauer study, the increase of NFO amount enhanced the hyperfine field intensity of tetrahedral Fe³⁺ ions at the expense of octahedral ones. NFO doped glasses exhibited ferromagnetic behavior whose M_s and H_c increased with the NFO amount due to the NCs size effect. Verdet constant and Faraday rotation angle were studied as function of wavelength, magnetic field, polarizer angle and NFO amount. 3%NFO glass exhibited significant enhancement in magnetization and Verdet constant of 91 rad/T.m at 633 nm which is 5-fold of host glass and superior than literatures. In addition, due to the nanoscale NCs, the thermal stability of obtained NFO glasses remained higher than 100 °C which is promising for photonics devices fabrication.     

Improved magnetic performance of Co-doped La2NiMnO6 ceramics prepared at low temperature

Co-doped La₂NiMnO₆ (La₂Co_xNi_1-xMnO₆, LC_xNMO, x = 0.1-0.5) ceramics were fabricated at relatively low temperature of 700 °C, to obtain double-perovskite with remarkable magnetic performance. It was found that the LC_xNMO ceramics in P2₁/n and R-3 phases could be well densified, with high relative density (>99 %) and fine grain size (0.5−1 μm). An increasement in cell volume was observed with the doping of Co, and the valence state changed from (Mn³⁺ + Ni³⁺/Co³⁺) to (Mn⁴⁺ + Ni²⁺/Co²⁺), revealing the improvement of B-site cations ordering. Moreover, the smaller grains resulted from the lower sintering temperature also decreased the level of antisite disordering. Consequently, the value of M_S/M_theo was significantly improved from 75.49% to 88.36 % by optimizing Co-doping concentration while the Curie temperature was still rather high (>250 K). The LC_0.5NMO ceramic was found to have the maximum M_S (4.86 μ_B/f.u.), attributing to the large B-site ordering because of higher Mn⁴⁺ and Ni²⁺/Co²⁺ content.     

Room temperature multiferroicity in Aurivillius compounds Bi6Fe2−xNixTi3O18 (0≤x≤1)

We investigate the structural, magnetic, ferroelectric, and dielectric properties of Bi₆Fe_2−xNi_xTi₃O₁₈ (0≤x≤1). The coexistence of ferroelectricity and ferromagnetism were observed at room temperature for the Ni-doped samples. The ferromagnetism in Bi₆Fe_2−xNi_xTi₃O₁₈ can be understood in terms of spin canting of the antiferromagnetic coupling of the Fe-based and Ni-based sublattices via Dzyaloshinsky-Moriya interaction. Moreover, the substitution of Ni for Fe was effective for the enhancement of ferroelectric properties. The x=0.6 sample exhibits a maximum remnant polarization P_r of 37.8 μC/cm² because of a lower leakage current. The rather large activation energy in the x=0 and 0.2 samples implies that the relaxation process may be not associated with the thermal motion of oxygen vacancies inside the bulk.     

Effect of La and Ni substitution on structure,dielectric and ferroelectric properties of BiFeO3 ceramics

In this communication, we present the results on Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples processed by solid-state reaction route in order to study crystalline and electronic structure, dielectric and ferroelectric properties. The best refinement was achieved by choosing rhombohedral structure (R3c) for BiFeO₃ and Bi_0.9La_0.1FeO₃ samples. Whereas, the XRD pattern of BiFe_0.95Ni_0.05O₃ and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ samples were refined by choosing rhombohedral (R3c) and cubic (I23) structure. Raman scattering measurement infers nine Raman active phonon modes for all the as prepared samples. The substitution of Ni ion at Fe-site in BiFeO₃ essentially changes the modes position i.e. all the modes are observed to shift to lower wave number. Dielectric constant (ε′) and dielectric loss (tan δ) as a function of frequency have been investigated and they decreases with increasing frequency of the applied alternating field and become constant at high frequencies. This feature is a characteristic of Maxwell Wagner type of interfacial polarization. The remnant polarization (P_r) for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.08, 0.11, 0.69 μC/cm², respectively and the value of coercive field for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.53, 0.67, 0.68 kV/cm, respectively. X-ray absorption spectroscopy (XAS) experiments at Fe L₂,₃ and O K-edges are performed to investigate the electronic structure of well-characterized Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples. The presence of reasonable ferroelectric polarization at room temperature in Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ ceramics makes it suitable for technological applications.     

Effect of Nb substitution on magnetic,ferroelectric and photocatalytic properties of Bi0.95Sm0.05Fe1-xNbxO3 (0 ≤ x ≤ 0.1) nanoparticles

The single phase Bi_0.95Sm_0.05Fe_1-xNb_xO₃ (0 ≤ x ≤ 0.1) nanoparticles were synthesized by the sol-gel route, and the effect of Nb substitution on their magnetic, ferroelectric and photocatalytic properties were studied. X-ray diffractometry confirms a phase transformation from rhombohedral to orthorhombic with an increase in Nb substitution. The grain size decreases significantly, and the morphology of grains becomes homogeneous with the increase of Nb concentration. The maximum remnant magnetization (0.014 emu/g), coercivity (565 Oe) and polarization (0.592 μC/cm²) are observed in Bi_0.95Sm_0.05Fe_0.9Nb_0.1O₃. It has been observed that the energy band gap has been slightly reduced from 2.14 to 2.03 eV with Nb substitution, indicating an improvement of photocatalytic activity. The methylene blue degradation is used to represent the photocatalytic ability of Bi_0.95Sm_0.05Fe_1-xNb_xO₃ nanoparticles. The highest degradation efficiency (~74%) of methylene blue is obtained in Bi_0.95Sm_0.05Fe_0.93Nb_0.07O₃, which is much higher than that of Bi_0.95Sm_0.05FeO₃ (~51%) and can be attributed to the optimum particle size and the smallest energy band gap.     

Novel Bi4O5Br2/MnxZn1-xFe2O4 magnetic composite with an enhanced photodegradation activity and excellent recyclability

Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ nanocomposites with impressive photocatalytic and recyclability properties were synthesised using a microemulsion method. In addition to the photocatalytic effect, the crystal structure and morphology, photoelectrochemical characteristics, magnetic effect and photocatalytic mechanism of Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ were also investigated. As the best sample, the removal rate of the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ photocatalyst with 7.5 wt% Mn_xZn_1-xFe₂O₄ to rhodamine B (RhB) reached up to 99.4% within 60 min. The enhanced photocatalyst activity was mainly attributed to the type-II heterojunction formed between Bi₄O₅Br₂ and Mn_xZn_1-xFe₂O₄, which not only optimised the energy band structure, but also led to the building of an interior electromagnetic field within the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ heterojunction. Meanwhile, the constantly producing and migrating h⁺ and ·O₂^? were the main active components. In particular, the results of the saturation magnetization tests and magnetic recovery experiments revealed that the magnetic composite photocatalyst can be recovered effectively. The results of the removal rate of RhB remaining at 85.2% after five uses reflected the advantages of the stability of the Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ photocatalyst. In brief, this paper presented an original idea to develop a novel composite magnetic photocatalyst and research the enhancement mechanism of photocatalysis.     

Copper substituted nickel ferrite nanoparticles anchored onto the graphene sheets as electrode materials for supercapacitors fabrication

Nickel ferrites with high theoretical capacitance value as compared to the other metal oxides have been applied as electrode material for energy storage devices i.e. batteries and supercapacitors. High tendency towards aggregation and less specific surface area make the metal oxides poor candidate for electrochemical applications. Therefore, the improvements in the electrochemical properties of nickel ferrites (NiFe₂O₄) are required. Here, we report the synthesis of graphene nano-sheets decorated with spherical copper substituted nickel ferrite nanoparticles for supercapacitors electrode fabrication. The copper substituted and unsubstituted NiFe₂O₄ nanoparticles were prepared via wet chemical co-precipitation route. Reduced graphene oxide (rGO) was prepared via well-known Hummer's method. After structural characterization of both ferrite (Ni_1-xCu_xFe₂O₄) nanoparticles and rGO, the ferrite particles were decorated onto the graphene sheets to obtain Ni_1-xCu_xFe₂O₄@rGO nanocomposites. The confirmation of preparation of these nanocomposites was confirmed by scanning electron microscopy (SEM). The electrochemical measurements of nanoparticles and their nanocomposites (Ni_0.9Cu_0.1Fe₂O₄@rGO) confirmed that the nanocomposites due to highly conductive nature and relatively high surface area showed better capacitive behavior as compared to bare nanoparticles. This enhanced electrochemical energy storage properties of nanocomposites were attributed to the graphene and also supported by electrical (I-V) measurements. The cyclic stability experiments results showed ~65% capacitance retention after 1000 cycles. However this retention was enhanced from 65% to 75% for the copper substituted nanoparticles (Ni_0.9Cu_0.1Fe₂O₄) and 65–85% for graphene based composites. All this data suggest that these nanoparticles and their composites can be utilized for supercapacitors electrodes fabrication.     

Effect of Ni2+ substitution on structural,magnetic, dielectric and optical properties of mixed spinel CoFe2O4 nanoparticles

Nanoparticles of Co_1−xNi_xFe₂O₄ with x=0.0, 0.10, 0.20, 0.30, 0.40 and 0.50 were synthesized by co-precipitation method. The structural analysis reveals the formation of single phase cubic spinel structure with a narrow size distribution between 13–17 nm. Transmission electron microscope images are in agreement with size of nanoparticles calculated from XRD. The field emission scanning electron microscope images confirmed the presence of nano-sized grains with porous morphology. The X-ray photoelectron spectroscopy analysis confirmed the presence of Fe²⁺ ions with Fe³⁺. Room temperature magnetic measurements showed the strong influence of Ni²⁺ doping on saturation magnetization and coercivity. The saturation magnetization decreases from 91 emu/gm to 44 emu/gm for x=0.0–0.50 samples. Lower magnetic moment of Ni²⁺ (2 µ_B) ions in comparison to that of Co²⁺ (3 µ_B) ions is responsible for this reduction. Similarly, overall coercivity decreased from 1010 Oe to 832 Oe for x=0.0–0.50 samples and depends on crystallite size. Cation distribution has been proposed from XRD analysis and magnetization data. Electron spin resonance spectra suggested the dominancy of superexchange interactions in Co_1−xNi_xFe₂O₄ samples. The optical analysis indicates that Co_1−xNi_xFe₂O₄ is an indirect band gap material and band gap increases with increasing Ni²⁺ concentration. Dispersion behavior with increasing frequency is observed for both dielectric constant and loss tangent. The conduction process predominantly takes place through grain boundary volume. Grain boundary resistance increases with Ni²⁺ ion concentration.     

Lead-free BLTO/NMFO magnetoelectric composite films prepared by the sol-gel method

The lead-free ferroelectric films of Bi_4?xLa_xTi₃O₁₂(BLTO) and ferromagnetic films of Ni_1?xMn_xFe₂O₄(NMFO) were prepared on Pt/Ti/SiO₂/Si substrate by means of the sol-gel and spin-coating method. The lead-free magnetoelectric composite films with the structure of Bi_3.4La_0.6Ti₃O₁₂/Ni_0.7Mn_0.3Fe₂O₄/substrate (BN) and Ni_0.7Mn_0.3Fe₂O₄/Bi_3.4La_0.6Ti₃O₁₂/ substrate (NB) were also deposited on Pt/Ti/SiO₂/Si substrate. The X-ray diffraction results show that two composite films possess BLTO and NMFO phases without any intermediate phase. The SEM images show that two composite films exhibit layered structure, clear interface and no transition layer between BLTO and NMFO films. Two composite films exhibit both good ferromagnetic and ferroelectric properties, as well as magnetoelectric coupling effect. The deposition sequence of ferroelectric and ferromagnetic films in the composite films has significant influence on the ferroelectric, ferromagnetic and magnetoelectric coupling properties of the composite films. The values of magnetoelectric voltage coefficient of the BN composite films are higher than those of the NB composite films at any fixed H_bias.     

Preparation and properties of sol–gel synthesized Mg-substituted Ni2Y hexagonal ferrites

A series of single phased Y-type hexagonal ferrites Sr₂Ni_2?xMg_xFe₁₂O₂₂ (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by the sol–gel auto combustion method. The effects on structural, magnetic and electrical properties have been investigated by substituting Mg²⁺ at Ni²⁺ sites. The X-ray diffraction (XRD) patterns confirm single phase Y-type hexaferrite and various parameters such as lattice constants, cell volume, X-ray density, bulk density and porosity have been calculated from XRD data. The Fourier transform infrared (FTIR) spectra show the characteristics absorption ferrite peaks of the sintered sample. The microstructure was studied by scanning electron microscopy (SEM). All the ferrites show a hexagonal platelet-like shape which is a most suitable shape for microwave absorption. The dielectric constant followed the Maxwell–Wagner interfacial polarization and relaxation peaks were observed in the dielectric loss properties. The room temperature dc electrical resistivity and activation energy were found to decrease for samples x=0.1, 0.2 and increase for the rest of samples hence making these materials suitable for multilayer chip inductors (MLCIs). A soft magnetic behavior was revealed by M–H loops. Saturation magnetization (M_s), retentivity (M_r), coercivity (H_c) and magnetic moment (n_B) were found to decrease as the Mg²⁺ contents increased.     

Synthesis,structural, electrical and magnetic properties of Bi2Fe4-xGaxO9 (0 ≤ x ≤ 1.6)

We investigate the electrical and magnetic properties of the Bi₂Fe_4-xGa_xO₉ (0?≤?x?≤?1.6) polycrystalline samples synthesized via solid-state reaction technique. Magnetic susceptibility measurements reveal that lightly doped samples (x?<?0.8) undergo successive transitions, from high-temperature paramagnetic to antiferromagnetic phase followed by a low-temperature spin-glass state while the samples with heavy doping (x?>?0.8) demonstrate paramagnetic to spin-glass (SG) transition. The variation of irreversible temperature obtained from zero field cooling (ZFC) and field cooling (FC) susceptibilities versus measured magnetic field and low-temperature magnetic hysteresis (M-H) loops support the existence of spin-glass phase. The dielectric constant (?_r) of Bi₂Fe_4-xGa_xO₉ with Ga-dilution reveals a weak-temperature sensitivity in high-temperature range (300?K?≤?T?≤?550?K), which is advantageous for high temperature capacitor applications and electronic devices.