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This work reports the simultaneous observation of converse magnetoelectric (CME) and direct magnetoelectric (DME) effects in LaYFe2O6. The structural, magnetic, and magnetoelectric properties of LaYFe2O6, prepared by the sol-gel auto-combustion method and sintered at various temperatures, have been studied. The x-ray powder diffraction study suggests the double perovskite structure with symmetries P21nm (∼90%) and Pbnm (∼10%). The alternate ordering of La and Y ions is confirmed by the neutron powder diffraction (ND) study, which also suggests the antiferromagnetic (AFM) ordering of spins. AFM behavior is also manifested by the magnetic field-dependent magnetization (M) measurement. A higher P21nm phase content is desirable in the context of magnetoelectricity. Magnetic transition (∼700 K) is asserted in the temperature-dependent M measurement. The isothermal magnetization study shows weak ferromagnetism probably due to gradually increasing spin canting with temperature until the transition temperature. The highest CME coefficient (∼2.26 mOe cm/V) as well as DME coefficient (∼0.45 mV/cm Oe) in this material are recorded. True magnetoelectricity for temperature as high as 400 K opens up a new avenue on the playground of magnetoelectric (ME)-based applications. [ABSTRACT FROM AUTHOR]

This work represents an effective approach to witness the true impedance profiles of the material. Here, a double-perovskite material LaYFe2O6 is prepared by the sol–gel auto-combustion method, which is characterized by the x-ray diffraction (XRD), field emission scanning electron microscope (FESEM), thermogravimetric analysis (TGA)–differential scanning calorimetry (DSC), and electrochemical impedance spectroscopy (EIS) technique. The XRD measurement confirms the successful synthesis of the said material with orthorhombic crystal structure having symmetry P21nm (~ 90%) and a slight contribution from Pbnm phase (~ 10%). The FESEM image suggests porous nature of the sample having grain size ~ 150 nm, sintered at 1473 K. TGA with simultaneous DSC measurement shows slight but gradual mass loss (related to adsorbed gases/vapors) above 400 K. The EIS shows influence of the adsorbed gases/vapors in the pores of the pellet on the impedance data. In this context, a homemade open-atmospheric impedance measurement setup is developed. The EIS measurement are done for (1) as-prepared sample, (2) sample preheated to 473 K before performing EIS, and (3) sample preheated to 400 K under vacuum. The process giving best result (having minimum effect of the adsorbed gases on the observed impedance spectra) is found by following the method (2). [ABSTRACT FROM AUTHOR]

La2NiMnO6 prepared under ambient conditions are analyzed for their crystal phase symmetry via powder x-ray diffraction in the laboratory as well as synchrotron sources and neutron powder diffraction. The room temperature symmetry is found to be R − 3 c for samples having a sintering temperature less than 800 °C and gradually increasing participation of P 2 1 / n symmetry is observed for higher sintering temperature samples. A crystallographic phase transition at ∼650 K from biphasic (R − 3 c + P 2 1 / n) to monophasic (R − 3) for all samples is observed. This transition is found to be endowed with a small amount of magnetic ordering at the transition temperature. The measured magnetoelectricity on these samples displayed their direct dependence on relative crystal phase symmetries, such that magnetoelectricity is highest for the equifraction content of R − 3 c and P 2 1 / n symmetries. The temperature variation of the first order magnetoelectric coefficient is observed to be proportional to T − 0.25 , which is analogous to the Mott variable range hopping conduction exhibited by these compounds. Corroboration of observed results suggests the interfacial origin of magnetoelectricity in these samples. [ABSTRACT FROM AUTHOR]

Multiferroic polymer composites of La2NiMnO6 and poly(vinylidene fluoride) (PVDF) in the form of disks and thick films were made via a two-step method and a solution casting method, respectively. These composite samples are studied via powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM). The XRD data revealed the biphasic (P21/n + R-3c) crystal symmetry of La2NiMnO6 nanoparticles in the disk samples but monophasic (R-3c) crystal symmetry in the film sample. The formation of an electroactive β-phase of PVDF is observed in the FTIR spectra of a composite film sample. Estimation (via FTIR data) revealed the maximum β-phase fraction of PVDF (∼37%) and zero porosity (in FESEM images) for the film sample. The magnetoelectric (ME) voltage measurement on these composite samples show significant ME voltage for temperatures as high as 400 K, which otherwise is zero for T > 277 K in La2NiMnO6. Among the three composites, the film sample exhibited the maximum value of a first-order ME coefficient of 9.6 mV/cm Oe, and this value is at least two orders higher than that of the La2NiMnO6 pellet. Such a high value of ME coefficient favors this sample for its utilization in device applications and thus makes it technologically viable for ME based applications. [ABSTRACT FROM AUTHOR]

The present work reports an enhanced magnetoelectric (ME) effect at room temperature (RT) and above in a nanocomposite of LaYFe2O6/poly-(vinylidene fluoride)–hexafluoropropylene [LaYFe2O6/P-(VDF-HFP)], which is prepared by the solution-casting method. Field-emission scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy reveal excellent phase-to-phase connectivity and an enhanced beta-phase fraction in the PVDF matrix by the incorporation of 10 wt % antiferromagnetic nanoparticles (NPs). This is also substantiated by the improved ferroelectric (electric-field-dependent polarization) response by a 10 wt % sample. At RT, this nanocomposite manifests a first-order ME coupling coefficient of ∼2.92 mV cm–1 Oe–1 and a second-order ME coupling coefficient of ∼0.051 μV cm–1 Oe–2 (significantly 1 order higher than that of pristine LaYFe2O6). The enhanced ME coefficient at RT and above makes it a viable candidate to address the challenges of ME-based device applications. A flexible, portable, lightweight, cost-effective magnetoelectric nanogenerator (MENG) fabricated from the nanocomposite film is able to harvest the wasted magnetic energy with an efficiency of 1.5%. As a demonstration, the harvested electric energy is stored in a capacitor, which, in turn, is used to power a light-emitting diode (LED). The present work hence suggests the deployment of this material for self-powered wearable devices. [ABSTRACT FROM AUTHOR]

In this study, manganese substituted strontium hexaferrite (SrFe12−xMnxO19; x = 0, 3, 5, and 7) prepared by the sol–gel auto-combustion method are studied. We observed that the substituted Mn preferentially goes to the 2a and 12k sites of Fe. Raman modes related to the 12k site suggest the stiffening of the lattice. The transformation of the grain's shape from hexagonal (x = 0 and 3) to rhombohedral (x = 7) was observed, as shown in the micrographs obtained from FESEM. The thermomagnetic curves show the shift of TC to lower temperatures with the increase in the Mn content. From x = 5 onwards, the growth of another magnetic phase (FiM2) of lower coercivity apart from the parent phase (FiM1) of higher coercivity is seen. The FiM2 phase was found to increase with the Mn content in the sample (16.4(3)% for x = 5 but 66.2(5)% for x = 7). Although the magnetization for both FiM1 and FiM2 decreases with the increase in temperature, both magnetic phases behave in contrast to each other for x = 5 and x = 7. The study suggests a transformation of the compound from high magnetic anisotropy (x = 0) to low magnetic anisotropy (x = 7). The x = 5 composition sample displays the highest value of the first-order ME coefficient (0.83(2) mV × cm−1 × Oe−1). The observed value for x = 5 composition is ∼2.5 times higher than that of the parent x = 0 composition sample (0.33(2) mV × cm−1 × Oe−1). The studies thus suggest that the x = 5 composition is one of the viable candidates for magnetoelectric applications. [ABSTRACT FROM AUTHOR]

A systematic study of near room temperature magnetoresistance (MR) behavior is carried out for magnetoelectric CoFe2O4-BiFeO3 core-shell nanoparticles. The analysis of MR data reveals that the MR is guided by the anisotropic magnetoresistance (AMR) and the giant magnetoresistance (GMR) effect. The GMR effect is predominant in the sample having a maximum shell thickness, whereas the AMR effect dominates the least shell thickness and bare CoFe2O4. Analysis of the MR data in conjunction with the resistivity suggests that the electrical conduction in these samples is due to (a) tunneling and (b) hopping of electrons across the domains. The impedance and modulus spectra analysis shows that the core-shell particles as a whole are participating in the relaxation process, thus indicating a strong coupling between the core and shell, which may be highly desirable while fetching their magnetoelectric based applications. [ABSTRACT FROM AUTHOR]

La2NiMnO6 is prepared for two different sintering time durations: 4 hour (4H) and 24 hour (24H). The magnetization data suggest a double ferromagnetic (FM) transition for 24H, whereas a single FM transition for 4H sample. The 4H sample was found to possess several microscopic pores compared with the 24H sample, and thus, these pores are vacuum impregnated with polyvinylidene fluoride (PVDF). The PVDF in the impregnated sample is found to crystallize in beta phase. The first and second order magnetoelectric coefficients are extracted from the measured data and plotted as a function of temperature. The room temperature region is found to be dominated by the magnetoconductivity/magnetoloss and thus resulting low ME voltage. With lowering of temperature, the situation improves, and for T < 200 K, the loss component becomes negligible so that the true magnetoelectricity is observed. A comparative study on all the three samples (4H, 24H, and 4H + PVDF) shows a significant enhancement in the magnetoelectricity in the 4H + PVDF sample. The highlight of this report is the unique way to arrest the porosity by PVDF impregnation into the pores of La2NiMnO6 so that leakage is minimized. [ABSTRACT FROM AUTHOR]

This work provides an effective approach to increase the magnetoelectric (ME) operating temperature of primordial sesqui oxide Cr2O3. The CoFe2O4 (core)/Cr2O3 (shell) nanoparticles with varying molar fractions are prepared via the sol-gel auto-combustion method. The phase-purity and coating induced micro-strains in core as well as shell have been validated from the Rietveld refinement of x-ray diffraction data, and are complementary to the Fourier transform infrared spectroscopy and Raman spectroscopy studies. Transmission electron microscopy measurement confirms the core/shell configuration of the nanoparticles. The magnetization measurements suggest screening of ferromagnetic interaction of CoFe2O4 (core) due to Cr2O3 shell over it, such that core/shell nanoparticles respond like single domain particles. A careful inspection of the impedance and modulus data suggest single relaxation in the studied frequency/temperature range for all the compositions. Both, the relaxation and the conduction processes are found to be polaronic obeying Mott variable range hopping mechanism. Direct ME measurements on these samples manifests the presence of linear magnetoelectricity for temperature as high as 400 K―a hallmark of enhancement in ME operating temperature of parental Cr2O3 phase and therefore widen its scope to meet the necessity of ME based potential applications. [ABSTRACT FROM AUTHOR]

CoFe2O4 (core)/BiFeO3 (shell) nanoparticles are prepared by varying the relative molar concentration of core and shell materials (40%CoFe2O4-60%BiFeO3, 50%CoFe2O4-50%BiFeO3, and 60%CoFe2O4-40%BiFeO3). The core-shell nature is confirmed from transmission electron microscopy on these samples. A plot of ΔM (=MFC-MZFC) vs temperature suggests the presence of two types of spin dynamics: (a) particle size dependent spin blocking and (b) spin-disorder. These two spin dynamic processes are found to contribute independently to the generation of magnetoelectric voltage. Very clear first order and second order magnetoelectric voltages are recorded. The resemblance of the first order magnetoelectric coefficient vs temperature plot to that of building up of order parameters in the mean field theory suggests that spin disorder can act like one of the essential ingredients in building the magnetoelectric coupling. The best result is obtained for the 50-50 composition sample, which may be due to better coupling of magnetostrictive CoFe2O4, and piezoelectric BiFeO3, because of the optimum thickness of shell and core. [ABSTRACT FROM AUTHOR]

This work reports the simultaneous observation of converse magnetoelectric (CME) and direct magnetoelectric (DME) effects in LaYFe2O6. The structural, magnetic, and magnetoelectric properties of LaYFe2O6, prepared by the sol-gel auto-combustion method and sintered at various temperatures, have been studied. The x-ray powder diffraction study suggests the double perovskite structure with symmetries P21nm (∼90%) and Pbnm (∼10%). The alternate ordering of La and Y ions is confirmed by the neutron powder diffraction (ND) study, which also suggests the antiferromagnetic (AFM) ordering of spins. AFM behavior is also manifested by the magnetic field-dependent magnetization (M) measurement. A higher P21nm phase content is desirable in the context of magnetoelectricity. Magnetic transition (∼700 K) is asserted in the temperature-dependent M measurement. The isothermal magnetization study shows weak ferromagnetism probably due to gradually increasing spin canting with temperature until the transition temperature. The highest CME coefficient (∼2.26 mOe cm/V) as well as DME coefficient (∼0.45 mV/cm Oe) in this material are recorded. True magnetoelectricity for temperature as high as 400 K opens up a new avenue on the playground of magnetoelectric (ME)-based applications. [ABSTRACT FROM AUTHOR]