Magnetodielectric Studies Research Articles

Strong magnetodielectric effect in Bi(La)Fe(Cr)O3 multiferroic nanomaterials

The Bi1-xLaxFe1-yCryO3 (x = 0.00, 0.06; y = 0.00, 0.03, 0.06, 0.09, 0.12) nanomaterials have been synthesized using the simple solvo-thermal technique. The Rietveld refinement of XRD analysis using FullProf Software confirms that all synthesized materials follow rhombohedral perovskite crystal structure of R3C space group. The dielectric and ac conductivity data are analyzed to understand the role of grain and grain boundary contributions. The enhancement of magnetic properties has been observed from SQUID measurement for the co-doped samples at room temperature. Also, a significant improvement in polarization has been observed for the doped nanocompounds from the ferroelectric hysteresis loop. The magneto-dielectric study reveals a large improvement in our co-doped BFO nanomaterials and the value is nearly three times of those reported earlier. The calculated energy storage efficiency for the co-doped samples are found to have as high as 51 %. The sample with x = 0.06 and y = 0.09 with a magneto dielectric coefficient of around 30 % and energy storage efficiency of 35 % is the most suitable for both spintronic and energy storage devices.

An additional simultaneous magnetic ordering and magneto-capacitive behavior with dielectric relaxation besides multiferroicity in FeTe x VO4

Here we report the evidence of an additional magnetic ordering and frequency dispersive magneto-dielectric (MD) permittivity besides multiferroic behavior in Te4+ (S = 0) doped FeVO4. Two antiferromagnetic transitions similar to FeVO4 at ∼21.86 K (T) and 16.03 K (T) were observed in all samples. An additional novel defect clusters based magnetic ordering at relatively higher temperature (T) ∼ 203 K is also observed from the magnetization. Evaluated magnetic moments show systematic decrease and the magnetic frustration factors show an increase with the increasing of Te4+ (S = 0) content. MD studies show stable ferroelectric ordering at spiral magnetic transition (T) and the multiferroic order persists to the largest doping of Te (x = 0.10). The MD studies also reveal a magneto-capacitive (MC) behavior at T (∼203 K) with a high dielectric constant and loss, and the possible reason for the magnetic ordering and MC behavior is ascribed to short range magnetic clustering arising out of defect based mechanisms. Mössbauer spectroscopic studies confirm local structural correlation with magnetic and ferroelectric ordering.

Direct magnetoelectric and magnetodielectric studies of electrospun Ba2Ni2Fe12O22–Pb(Zr0.52Ti0.48)O3 core–shell nanofibers

This article reports the synthesis of barium nickel hexaferrite-lead zirconium titanate (Ba2Ni2Fe12O22-Pb(Zr0.52Ti0.48)O3) core-shell nanofibers through sol-gel electrospinning method. Direct magnetoelectric and magnetodielectric coupling studies were performed on the synthesized electrospun core-shell nanofibers. The structure, functional, morphological, magnetic, dielectric, leakage current, and ferroelectric properties were also analyzed. X-ray diffraction studies revealed the hexagonal crystal structure of the core and the tetragonal structure of the shell. The Fourier transform infrared spectroscopy analysis showed the fundamental functional groups present in the nanofibers. Scanning electron microscopy studies showed that the diameter of the nanofibers was 404 nm, and elemental analysis by energy-dispersive X-ray spectroscopy showed the stoichiometric formation of Ba2Ni2Fe12O22 and Pb(Zr0.52Ti0.48)O3 in the composite. Microstructure studies using a transmission electron microscope revealed the formation of core-shell nanofibers with a clear interface between the magnetic Ba2Ni2Fe12O22 (BNFO) core and the ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) shell. Selected-area electron diffraction analysis showed the Ba2Ni2Fe12O22 and Pb(Zr0.52Ti0.48)O3 phases to be highly crystalline. At room temperature, the synthesized nanofibers exhibited well-defined ferroelectric and magnetic hysteresis loops. Dielectric and leakage current studies were performed. Direct magnetoelectric and magnetodielectric studies were also performed to study the cross-coupling between the ferroic orders of the nanofiber. Moreover, using Landau’s energy expression, the type of magnetoelectric coupling was proved to be biquadratic. The enhanced magnetoelectric behavior of the Ba2Ni2Fe12O22–Pb(Zr0.52Ti0.48)O3 core–shell nanofiber confirms that the nanofiber is a potential candidate for high-performing magnetic field sensors, magnetically tuned capacitors, multimedia transducers, and spintronic devices.

Evaluation of dielectric, energy storage and multiferroic properties of PrFeO3-PbTiO3 solid solutions

This work promotes the room temperature energy storage properties of the multiferroics. In this approach, impacts of PrFeO3 doping on PT-based solid solutions (Pb[Formula: see text][Formula: see text]Pr[Formula: see text]Ti[Formula: see text][Formula: see text]Fe[Formula: see text]O3, [Formula: see text] = 0.21, 0.22, 0.23, 0.24, 0.25 and 0.26) have been explored. X-ray diffraction (XRD) patterns were used to estimate the crystallographic parameters, confirming the single phase tetragonal structure. The ferroelectric Curie temperature ([Formula: see text][Formula: see text]) is observed to drop from 410 K to below room temperature as the Pr concentration increases. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The sample [Formula: see text] = 0.24 achieved the maximum value of energy storage density of 362.25 mJ/cm3 with the efficiency of 40.5%. The ferroelectric P-E loops were used to determine the energy storage values at room temperature. The validity of magnetoelectric coupling in all samples was confirmed by magneto-dielectric studies and found that the sample [Formula: see text] = 0.24 shows the maximum response with the coupling coefficient ([Formula: see text]) = 15.54 g2/emu2.

Enhanced magnetic and magnetodielectric behavior in morphologically distinct BTFO and LSMO composites

In this work, sol–gel modified technique is used to synthesize the (1-x)BTFO-(x)LSMO composites (x = 0, 0.1, 0.2, 0.3, and 0.4). The composite's dual (BTFO and LSMO) phases are verified using X-ray diffraction analysis. A scanning and transmission electron microscope is used to analyze the distinct morphology of the two phases that demonstrated the plate-like grains and quasi-spherical particles of BTFO and LSMO phases in the composites, respectively. The magnetic studies reveal that the saturation magnetization (Ms ∼ 7.0 emu/g) and coercive field (Hc ∼ 1660 Oe) increased by nearly-three and 66 times for 40 % LSMO contained composite. The enhanced magnetic behavior is due to the interaction between the multiple magnetic ordering (AFM/FM) present in the prepared composites. The estimated values of squareness ratio (Mr/Ms) are lower than 0.5, illustrating the multi-domain nature of the composites. The switching field distribution (SFD) plot indicates that strong exchange coupling exists in the x = 0.4 composite compared to others. The change in dielectric permittivity at different magnetic fields is due to the magnetodielectric (MD) coupling in the composites. The field-dependent MD studies reveal that maximum MD strength (∼0.34 %) and minimum magnetoloss (ML) (∼0.02 %) are observed in x = 0.2 and 0.1 composites at 100 kHz, respectively. It is due to the non-collinear alignment of magnetic Mn ions at RT, which leads to the inverse Dzyalonskii-Moriya interaction. Additionally, the maximum MD coupling strength γ (-16.87 (emu/g)2) is observed in the x = 0.2 composite. The observed MD response in the composites is due to the dominating grain capacitive effect rather than the resistive effect, which is ascertained by the frequency-dependent magnetoresistance measurement. Hence, the composite's enhanced magnetic and magnetodielectric behavior makes it a suitable candidate for multifunctional device applications.

Synthesis of x[La0.67Sr0.33MnO3] – (1-x)[0.5Ba0.7Ca0.3TiO3-0.5BaZr0.2Ti0.8O3] multiferroic composite with its dielectric, magnetodielectric, magnetic and electrical conductivity studies

The present paper studies the synthesis and characterization of x[La0.67Sr0.33MnO3] – (1-x)[0.5Ba0.7Ca0.3TiO3-0.5BaZr0.2Ti0.8O3] multiferroic composite for x = 0.1 and 0.175. Parent materials of ferroelectrics Ba0.7Ca0.3TiO3 (BCT) and BaZr0.2Ti0.8O3 (BZT) and ferrite La0.67Sr0.33MnO3 (LSMO) have been prepared via hydroxide co-precipitation method while its composite x[LSMO] – (1-x)[0.5 BCT -0.5 BZT] was synthesized by ceramic route. The presence of ferroelectric and ferrite phases were confirmed by structural studies of composites. Microstructure shows the dense and closely packed LSMO particles over BCT-BZT ferroelectric phase. The dielectric properties of composites were studied in frequency range of 1KHz-1MHz and from room temperature to 500OC. P-E hysteresis loops of composites shows noticeable values of saturation polarization (Ps) and remnant polarization (Pr). Significant value of magnetoelectric (ME) coupling coefficient (α) of 2.15mV/cmOe was observed for the composite 0.175LSMO – 0.825(0.5BCT-0.5BZT) at 1 KHz frequency. Magnetodielectric (MD) properties of the composites were investigated by measuring the magnetocapacitance up to 1 T magnetic field. MD effect can be explained on the basis of contribution of dielectric constant due to interfacial polarization which depends on magnetic field and changes due to induced stress. Frequency dependent ac conductivity was confirmed by Jonscher's Universal Power law. Temperature dependent dc conductivity of the materials shows the Arrhenius behavior. As the ferrite content of LSMO increases in the composite saturation magnetization increases which can be studied by the hysteresis plot.

Electrochemical performance and large positive–negative magnetodielectric coupling in iron chromite spinels

• Current work is one of its kind study suggesting a material that can be used to fabricate a device that can simultaneously store memory and energy. • Low cost sol–gel method is used to synthesize iron chromite nanocrystals by varying Fe/Cr ratio. • Spinel phase i.e. FeCr 2 O 4 is observed at Fe/Cr ratios of 0.45, 0.6 and 0.65. • Magneto dielectric (MD) studies confirm positive MD constant at 0.45, 0.6 & 0.65 Fe/Cr ratios. • The galvanostatic charging/discharging behavior shows capacitive behavior of FeCr 2 O 4 samples. • The electrochemical results suggest that synthesized nanocrystals have potential for energy storage system. Spinel ferrites with remarkable electrochemical performance and magnetodielectric (MD) coupling are promising candidates for energy storage and spintronic devices. This study focuses on structural phases, dielectric and magnetic polarization along with magnetodielectric (MD) coupling and electrochemical response of Fe-Cr spinels. Low cost sol–gel method is used to synthesize iron chromite nanopowders. Iron to chromium (Fe/Cr) ratio is varied in the range of 0.2–0.65 (with interval of 0.05). XRD patterns confirm the formation of phase pure FeCr 2 O 4 at Fe/Cr ratios of 0.45, 0.6 & 0.65. Amorphous behavior is observed at Fe/Cr ratios of 0.2, 0.25, 0.5 & 0.55. Mixed phases are observed at 0.3, 0.35 & 0.4 Fe/Cr ratios. Formation of pure spinel phase at Fe/Cr ratio of 0.45 results in high saturation magnetization of 9.2 emu/g. High grain boundary resistance (189.62kΩ) and high dielectric constant (∼83.38 at log f = 5.0) along with low tangent loss (0.00423 at log f = 5) are observed at Fe/Cr ratio of 0.45. Magneto dielectric studies confirm positive magneto dielectric constant (MDC) of synthesized nanopowders at 0.45, 0.6 & 0.65 Fe/Cr ratios. Cyclic voltammetry is performed at constant potential window. Oxidation/reduction process leads to the pseudo-capacitive response of the material. The cyclic voltammetry curves show specific capacitance of 156 Fg −1 , 144 Fg −1 and 152 Fg −1 at scan rate of 25 mV/s at Fe/Cr ratios of 0.45, 0.6 & 0.65 of FeCr 2 O 4 nanopowders, respectively. The galvanostatic charging/discharging behavior shows capacitive behavior of FeCr 2 O 4 nanopowders. The electrochemical results suggest that synthesized nanopowders have potential for energy storage system.

Multilayer Gradient Perforated Radar Absorbing Structure for Stealth Applications

In the exploration of broadband radar absorbing structure (RAS), a new kind of multilayer gradient perforated RAS constituted of magnetic iron metal (Fe) and silicon carbide (SiC) is examined utilizing a top-down fabrication technique and metaheuristic grey wolf optimization (GWO) algorithm. The investigation of proposed structures and magneto-dielectric study of samples is carried out in 8.2 to 12.4 GHz (i.e., X-band). Distinct single and multilayered RASs are optimized using the GWO algorithm under certain restrictive conditions. In addition, the GWO algorithm is reinforced with a fitness function to acquire maximum bandwidth below -10dB threshold (RC≤-10 dB) in various oblique angles of incidence with a minimum coating thickness (t≤2.0 mm). Among all investigated RASs, triple-layer gradient perforated structure (TLGPS) is found to be effective which fulfills the lightweight, broadband, and angular stable behavior of an efficient absorber. TLGPS has considerably exhibited the concept of impedance gradient which assists in triumph broadband radar absorbing materials (RAMs) for low observable applications.

Investigation of the Phase Transitions and Magneto-Electric Response in the 0.9(PbFe0.5Nb0.5)O3-0.1Co0.6Zn0.4Fe1.7Mn0.3O4 Particulate Composite

Multiferroic composites with enhanced magneto-electric coefficient are suitable candidates for various multifunctional devices. Here, we chose a particulate composite, which is the combination of multiferroic (PbFe0.5Nb0.5O3, PFN) as matrix and magnetostrictive (Co0.6Zn0.4Fe1.7Mn0.3O4, CZFMO) material as the dispersive phase. The X-ray diffraction analysis confirmed the formation of the composite having both perovskite PFN and magnetostrictive CZFMO phases. The scanning electron micrograph (SEM) showed dispersion of the CZFMO phase in the matrix of the PFN phase. The temperature-dependent magnetization curves suggested the transition arising due to PFN and CZFMO phase. The temperature-dependent dielectric study revealed a second-order ferroelectric to the paraelectric phase transition of the PFN phase in the composite with a small change in the transition temperature as compared to pure PFN. The magnetocapacitance (MC%) and magnetoimpedance (MI%) values (obtained from the magneto-dielectric study at room temperature (RT)) at 10 kHz were found to be 0.18% and 0.17% respectively. The intrinsic magneto-electric coupling value for this composite was calculated to be 0.14 mVcm−1Oe−1, which is comparable to other typical multiferroic composites in bulk form. The composite PFN-CZFMO exhibited a converse magneto-electric effect with a change in remanent magnetization value of −58.34% after electrical poling of the material. The obtained outcomes from the present study may be utilized in the understanding and development of new technologies of this composite for spintronics applications.

Coexistence of large negative and positive magnetodielectric response in Bi1−xCaxFe1−yTiyO3−δ nanoparticle ceramics

Magnetodielectric (MD) properties of as-prepared (AP) and air-annealed ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Fe}}_{1\ensuremath{-}y}{\mathrm{Ti}}_{y}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ nanoparticle ceramics made by spark plasma sintering process are investigated as a function of temperature. Aliovalent ${\mathrm{Ca}}^{2+}$ substitution at ${\mathrm{Bi}}^{3+}$ site creates oxygen vacancies (${\mathrm{V}}_{\mathrm{O}}$) in the lattice disrupting the intrinsic spin cycloid of ${\mathrm{BiFeO}}_{3}$, which are suppressed when the charge compensating ${\mathrm{Ti}}^{4+}$ is co-substituted. In addition, cation substitution reduces the grain size and increases surface oxygen vacancies. These lattice and surface ${\mathrm{V}}_{\mathrm{O}}$ defects play a significant role in enhancing the magnetic properties. Zero-field-cooled magnetization curves of all AP samples show a sharp Verwey-like transition at \ensuremath{\sim}120 K, which weakens on air-annealing. A coexistence of positive and negative MD [MD = $\frac{\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}(H)}{\ensuremath{\varepsilon}(H=0)}$; $\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}(H)=\ensuremath{\varepsilon}(H)\ensuremath{-}\ensuremath{\varepsilon}(H=0)$] response is observed, with the former dominating at 300 K and the latter at 10 K. As-prepared 5 at.% (10 at.%) Ca and Ca-Ti substituted ${\mathrm{BiFeO}}_{3}$ ceramics exhibit a maximum MD response of --10% (\ensuremath{\sim}+3%) at 10 K (300 K). Negative MD response diminishes for air-annealed ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Fe}}_{1\ensuremath{-}y}{\mathrm{Ti}}_{y}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ ceramics due to the reduction in ${\mathrm{V}}_{\mathrm{O}}$ concentration. Samples exhibiting dominant positive MD response show a similar trend for MD $vs$ H and ${M}^{2}$ vs H plots. This agreement between ${M}^{2}$ and $\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}(H)$ demonstrates a strong inherent MD coupling. On the contrary, negative MD does not follow this trend yet shows a linear relationship of MD vs ${M}^{2}$, suggesting a strong coupling between the magnetic and dielectric properties. Temperature-dependent MD studies carried out at 5 T show a gradual change from negative to positive values. Negative MD at low temperatures could be activated by the spin-lattice coupling, which dominates even at high frequency (1 MHz) under the applied field. Other contributions, including Verwey-like transition, magnetoresistance, and Maxwell-Wagner effects, do not influence the observed MD response. A prominent role of oxygen vacancies in altering the MD behavior of ${\mathrm{BiFeO}}_{3}$ is discussed in detail.

Magnetodielectric study of BiFeO3 synthesized by assisted high-energy ball milling

A magnetodielectric study of multiferroic bismuth ferrite (BiFeO3) was conducted to provide new insights into the interactions between the dielectric and magnetic properties. BiFeO3 was synthesized by high-energy ball milling for 5 h, followed by annealing at 600 °C. X-ray diffraction showed the presence of the bismuth ferrite phase together with small amounts of the secondary phase, mullite (Bi2Fe4O9). Vibration sample magnetometry (VSM) confirmed the antiferromagnetic behavior ascribed to the bismuth ferrite. LCR (Inductance, capacitance and resistance) analysis demonstrated space charge polarization behavior, and a magnetodielectric study revealed magnetically induced changes in the interfacial polarization's relaxation frequency in a frequency range of 100 Hz to 5· × 106 Hz that were attributed to the switching of the ferroelectric domains in the bismuth ferrite. The detection and mechanism of these frequency dispersion changes are discussed in detail.

Studies on structural, dielectric, impedance spectroscopy and magneto-dielectric properties of La0.7Ba0.3MnO3/P(VDF-TrFE) multiferroic (0–3) nanocomposite films

La0.7Ba0.3MnO3(LBMO)/poly(vinylidenefluoride-co-trifluoroethylene) [P(VDF-TrFE)] nano-composite films (0–3) of thickness 30 µm were casted with different volume percentage of LBMO nano particles in P(VDF-TrFE) polymer matrix. The dielectric, conductivity, impedance and magneto-dielectric studies of these films are presented here. The permittivity of composite film with 0.5% LBMO filler percentage increases compared to pure P(VDF-TrFE) film however, it decreases on further increase in LBMO filler percentage. The permittivity of these films is quite stable with increase in temperature up to 100 °C i. e. there is small increase in the high frequency permittivity from ~ 3 to ~ 4.5 with increase in temperature from 30 °C to 100 °C. The conductivity of the nanocomposite films obeys Johnscher’s law and the magnitude of conductivities are of order of 10−12 S cm−1 at 30 °C which indicates highly insulating nature of these films. Magneto-dielectric (MD) study of these composite films in 0–7000 Oe range for different volume percentage of LBMO are showing negative MD effect and a maximum of − 0.71% MD is observed at 7000 Oe for the 2% LBMO/P(VDF-TrFE) nanocomposite (0–3) films.

Citrate coated magnetite: A complete magneto dielectric, electrochemical and DFT study for detection and removal of heavy metal ions

The super paramagnetic iron oxide nanoparticles (SPIONs) such as magnetite (Fe3O4) appear as an emerging class of materials in the field of environmental remediation owing to its biocompatibility, high surface area, super paramagnetic properties and ease of reuse and recovery. However, susceptibility of bare Fe3O4 to oxidation and agglomeration limits its use as an adsorbent material in aqueous medium, which demands the surface capping of these Fe3O4 nanoparticles for effective adsorption performance. We have successfully capped Fe3O4 with sodium citrate with a purpose to develop a felicitous magnetic sorbent material containing abundant metal trap centers at its surface. The successful surface modification of Fe3O4 with citrate is noticeable from FT-IR, TGA, XRD, Zeta potential (DLS), SEM, EDX,TEM, DR-UV, and contact angle measurements. For the first time, we report electrical impedance spectroscopic studies on this capped magnetic nanoparticle to understand the capacitive behavior of super paramagnetic Fe3O4 and citrate@Fe3O4 nanoparticles. The cyclic voltammograms manifested the excellent electrochemical response of citrate@Fe3O4 modified glassy carbon electrode to mM concentrations of Pb2+, Cd2+ and Zn2+ ions with response in order Pb2+> Cd2+> Zn2+. Differential Pulse Voltammetry confirms the descent sensitivity towards Pb2+ ions at different concentration with a 0.3 µM detection limit. The adsorption of Pb2+ ions followed Langmuir isotherm model with maximum monolayer adsorption capacity of 58.93 mg g−1. To further validate the experimental adsorption results and the mode of interaction between Pb2+and citrate@Fe3O4, quantum calculations using density functional theory were performed which indicate a good coherence between experimental and theoretical data. The presence of abundant carboxyl and hydroxyl metal trap centers at the surface of citrate@Fe3O4 is responsible for its promising adsorption capacity for Pb2+ ions removal. Both experimental as well as theoretical results suggest that surface functionalization has a positive impact for detection of heavy metal ions and should be given prime importance while designing absorbent materials. The citrate@Fe3O4 nanoparticles exhibit outstanding stability and regeneration over various cycles of sorption.

Structural and magnetodielectric properties of BiFeO3-GdMnO3 multiferroics

We report on structural, microstructural, spectroscopic, dielectric, electrical, ferroelectric, ferromagnetic, and magnetodielectric coupling studies of BiFeO3–GdMnO3[(BFO)1–x –(GMO) x ], where x is the concentration of GdMnO3 (x = 0.0, 0.025, 0.05, 0.075, 0.1, 0.15, and 0.2), nanocrystalline ceramic solid solutions by auto-combustion method. The analysis of structural property by Rietveld refinement shows the existence of morphotropic phase boundary (MPB) at x = 0.10, which is in agreement with the Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) studies. The average crystallite size obtained from the transmission electron microscopy (TEM) and x-ray line profile analysis was found to be 20–30 nm. The scanning electron micrographs show the uniform distribution of grains throughout the surface of the sample. The dielectric dispersion behavior fits very well with the Maxwell-Wagner model. The frequency dependent phase angle (θ) study shows the resistive nature of solid solutions at low frequency, whereas it shows capacitive behavior at higher frequencies. The temperature variation of dielectric permittivity shows dielectric anomaly at the magnetic phase transition temperature and shifting of the phase transition towards the lower temperature with increasing GMO concentration. The Nyquist plot showed the conduction mechanism is mostly dominated by grains and grain boundary resistances. The ac conductivity of all the samples follows the modified Jonscher model. The impedance and modulus spectroscopy show a non-Debye type relaxation mechanism which can be modeled using a constant phase element (CPE) in the equivalent circuit. The solid-solutions of BFO-GMO show enhanced ferromagnetic-like behavior at room temperature. The ferroelectric polarization measurement shows lossy ferroelectric behavior. The frequency dependent magnetocapacitance and magnetoimpedance clearly show the existence of intrinsic magnetodielectric coupling. The (BFO)1–x –(GMO) x solid solutions with x = 0.025–0.075 show significantly higher magnetocapacitance and magnetoimpedance compared to the pure BFO.

Grain to Grain Epitaxy-Like Nano Structures of (Ba,Ca)(ZrTi)O3/ CoFe2O4 for Magneto–Electric Based Devices

Multiferroic nanocomposites with grain to grain epitaxy-like feature comprising of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT)/CoFe2O4 (CFO)/BCZT layers were deposited on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. To enhance strain coupling between the phases, vertically ordered continuous nanostructures with grain to grain epitaxy-like feature was achieved by careful choice of material and optimized growth conditions. The columnar grains between the BCZT/CFO and CFO/BCZT interface were optimized such that every column grew in an epitaxy-like growth with grain-over grain crystallographic relation even at nanoscale. Grain to grain epitaxy was evident from TEM analysis (inverse FFT analysis). Elastic strain coupling present between various vibrational modes of BCZT and CFO was confirmed by cross-sectional Raman studies. Ferroelectric polarization of 10 μC/cm2 and out-of-plane remnant magnetization (40emu/cc) was observed in the columnar structure. The morphologically coherent columnar structure of both the phases and the epitaxial registry at the interface of the composite significantly enhanced the strain coupling between the ferroelectric/ferromagnetic phases, which is evident from the magneto-dielectric studies with a 21% change in dielectric constant and the magneto-electric(ME) coefficients (620-840 mV/cm·Oe). The ME values indicate the existence of high elastic strain coupling in continuous columnar structures compared with granular structures with an incoherent interface. Enhanced magneto-electric coupling in these types of nanostructures can be of great potential in realizing devices like actuators and sensors.

Composition-dependent structural, electrical, magnetic and magnetoelectric properties of (1 − x)BaTiO3−xCoFe2O4 particulate composites

Multiferroic composite with the general formula (1 − x)BaTiO3−xCoFe2O4 (x = 0.05, 0.15, 0.25, 0.35 and 0.45) has been synthesized by a standard solid-state reaction route. Powder X-ray diffraction analysis confirms the existence of ferrite (spinel CoFe2O4) and ferroelectric (tetragonal BaTiO3) biphase without any impurity phases in the sintered composites. Microstructure of the composite displays two different grain sizes and shapes studied from SEM analysis. The composites show both ferroelectric and ferromagnetic ordering: the saturation magnetization (Ms) and retentivity (Mr) of the composite are improved with the increase in ferrite phase, while leakage current, ferroelectric and dielectric properties of the composites show a drop. Existence of coupling between ferroelectric and ferromagnetic ordering measured through magnetodielectric (MD) and magnetoelectric (ME) studies reveal an increase in % MD and ME coefficients with an increase in ferrite content. An enhanced ME coupling coefficient of 17 mV cm−1 Oe−1 has been realized at a dc magnetic field of 5 kOe with a ac frequency of 50 Hz in (1 − x)BaTiO3−xCoFe2O4 (x = 0.45) composite.

Evidence of magneto-electric coupling and electrical study of CFO modified BNT/BT composites

(1-x)(0.93Bi0.5Na0.5TiO3/0.07BaTiO3)-xCoFe2O4 ((1-x)BNT/BT-xCFO, where x = 0.1, 0.2, 0.3, 0.4 and 0.5) composite samples were synthesized by microwave assisted solid state reaction route and sintered at 1050 °C. X-ray diffraction study showed the presence of ferroelectric/ferromagnetic (FE/FM) phases without any peak of secondary phase. This was further confirmed by SEM study showing the presence of both FE/FM grains distinctly. Frequency dependent dielectric study showed maximum dielectric constant ("r) for the composite sample with x = 0.4. Polarization versus electric field (P-E) loop study revealed that maximum remnant polarization (2Pr = 1.75 μC/cm2) was found also for the 0.6BNT/BT-0.4CFO sample. Remnant magnetization (Mr) of the composite sample with x = 0.4 was found to be ∼7.81 emu/g. Magnetodielectric (MD) study of the 0.6BNT/BT-0.4CFO composite sample showed decrease in "r with the application of magnetic field and a MD effect of ∼2.4% (at 10 kHz) was found. Low leakage current value (∼10−4 A) was obtained in the 0.6BNT/BT- 0.4CFO composite sample. Change in piezoresponse force microscopy contrast after poling indicated on the changes in polarization of the ferroelectric domains. Reduction in Mr, observed in magnetic force microscopy contrast gave a clear evidence of presence of electric field induced magneto-electric (ME) coupling in the 0.6BNT/BT-0.4CFO composite sample.

Room temperature ferrimagnetism in Yb-doped relaxor ferroelectric PbFe2/3W1/3O3

We report ferrimagnetism and reentrant relaxor ferroelectricity near room temperature in a Yb-doped PbFe2/3W1/3O3 cubic perovskite. Structural analysis reveals the presence of a single cubic perovskite phase, with the Fm3¯m space group [lattice parameter: a = 8.0112(3) Å], and partial B-site ordering. The B-site ordering yields uncompensated magnetic moments in the antiferromagnetic structure of PbFe2/3W1/3O3 and ferrimagnetism near room temperature. An excess moment of ∼0.6 μB/B-site may be estimated from magnetic hysteresis curves recorded up to 50 kOe at 5 K. The temperature dependent magnetodielectric study reveals a sequential phase transition from a long-range ferroelectric state (across 280 K) to a short-range relaxor ferroelectric state (across 190 K). The long-range ferroelectric ordering is found to be more affected by the application of external magnetic fields than the relaxor phase.

Enhanced magneto dielectric effect on oxygen annealed geometrically frustrated spin-chain compound: Ca3Co2O6

In the present work we report on the magneto dielectric studies of oxygen annealed, one dimensional compound Ca3Co2O6. The magnetic and electrical properties were studied on the polycrystalline samples prepared by conventional solid state reaction method and annealed in oxygen atmosphere. The magnetization versus temperature curve shows paramagnetic behavior up to 30 K and interesting magnetic transitions below that temperature. A dielectric anomaly around 15 K was observed. The change in dielectric constant between 75 K and 100 K is not intrinsic and is due to the grain boundary contributions in the polycrystalline sample. Our results predict that annealing at oxygen atmosphere improve the physical properties of calcium cobaltates which are promising materials for magnetoelectric applications.

Magnetodielectric effect in rare earth doped BaTiO3-CoFe2O4 multiferroic composites

Magnetically switchable dielectric properties in functional multiferroic composites at room temperature is considered to be a great challenge in order to fabricate magnetoelectric devices. High magnetoelectric effect in such materials is possible provided ferroelectric phase is highly coupled to the magnetic phase. In this report, an attempt has been made to fabricate multiferroic composites (1-x) Ba0.95Ho0.05TiO3 – x CoDy0.1Fe1.9O4 (x = 0.03, 0.06 and 0.09) by solid state route, with tunable magnetodielectric properties. From XRD studies, a decrease in cell volume of CoDy0.1Fe1.9O4 phase is observed with the increase in Ba0.95Ho0.05TiO3 phase, which is responsible for higher magnetodielectric effect. In composites, an appreciable decrease in grain size is one of the main factor that drives the coupling between two ferroic phases. By the incorporation of Ho3+ ions in the BaTiO3 lattice, an increase in ε′ is observed, which resulted in improved magnetodielectric effect in composites. In composites, decrease in hopping length with the increase in ferrite phase, resulted in enhancement in dielectric constant. For all composites, the unsaturated ferroelectric hysteresis loops were observed due to the conducting nature of ferrite phase. The incorporation of Dy3+ ions in the CoFe2O4 expanded its lattice, resulting in strain, which highly affected the magnetic properties. The magnetocrystalline anisotropy of composites with multidomain structure was calculated by using Law of approach to saturation, which is directly related to coupling between two ferroic phases. Magnetodielectric studies revealed that the magnetic ordering of CoDy0.1Fe1.9O4 phase results in increase in number of polar domains of Ba0.95Ho0.05TiO3 phase and thereby improves the magnetodielectric effect. The overall results of this work established the unification of Ba0.95Ho0.05TiO3 and CoDy0.1Fe1.9O4 phases in multiferroic composites, with improved coupling, making them potential candidates for magnetoelectric devices.