Enhanced magneto-electric effect in manganite tricolor superlattice with artificially broken symmetry

The magneto-electric effect in magnetic materials has been widely investigated, but obtaining an enhanced magnetoelectric effect is challenging. In this study, tricolor superlattices composed of manganese oxides-Pr（0.9）Ca（0.1）MnO3,La（0.9）Sr（0.1）MnO3, and La（0.9）Sb（0.1）MnO3-on（001）-oriented Nb：SrTiO3 substrates with broken space-inversion and timereversal symmetries are designed. Regarding the electric polarization in the hysteresis loops of the superlattices at different external magnetic fields, both coercive electric field Ec and remnant polarization intensity Pr clearly show strong magneticfield dependences. At low temperatures（〈 120 K）, a considerable magneto-electric effect in the well-defined tricolor superlattice is observed that is absent in the single compounds. Both maxima of the magneto-electric coupling coefficients ？Ec and ？Pr appear at 30 K. The magnetic dependence of the dielectric constant further supports the magneto-electric effect. Moreover, a dependence of the magneto-electric effect on the periodicity of the superlattices with various structures is observed, which indicates the importance of interfaces. Our experimental results verify previous theoretical results regarding magneto-electric interactions, thereby paving the way for the design and development of novel magneto-electric devices based on manganite ferromagnets.

Dielectric relaxation and magneto-electric characteristics of lead-free double perovskite: Sm2NiMnO6

The polycrystalline sample of a double perovskite, Sm2NiMnO6 was synthesized by a solid-state reaction route. From the X-ray structural study, it is found that the structure of the material is monoclinic with lattice parameters: a = 4.1750(63) ?, b = 7.6113(63) ?, c = 5.9896(63) ?, and β = 112.70°. These parameters are very close to and consistent with those of such type of materials. The dielectric, impedance, AC conductivity, and electrical modulus properties of the sample were studied in the temperature range of 25–300℃ and the frequency range of 1 kHz–1 MHz. Typical relaxor behavior observed in the dielectric studies was confirmed by Vogel–Fulcher fitting. From the Nyquist plots, the temperature dependent contribution of grain and grain boundary effect was confirmed. The non-Debye type of relaxation was found using the complex impedance spectroscopy. The magnetic study revealed that the sample had paramagnetic behavior at room temperature. Magneto-electric(ME) coefficient was obtained by changing DC bias magnetic field. This type of lead-free relaxor ferroelectric compound may be useful for high-temperature applications.

What Connects Dark Matter and Black Holes?

Dark matter is a major component of the universe, about six times more abundant than ordinary visible matter. We measure the effects of its mass, but it escapes the telescopes. It has the particularity of emitting no radiation and interacting only by the action of gravity. The main purpose of this article is to try to answer what dark matter is: we conjecture that it is composed of magnetically charged neutrinos, true magnetic monopoles. But that requires a huge conceptual leap: Maxwell’s laws must be inverted and the electric charge becomes a magnetic charge. Asymmetric “reversed” Maxwell’s laws would provide the “dark” magnetic charge that would replace the electric charge. The very form of the Dirac equation, which imposed on ordinary matter that the particle carries an electric charge and obeys the principal properties of the electron, would impose in the dark matter that the “dark” particle obeys the main properties of a neutrino associated with a magnetic charge. The second aim of the article is to show that dark matter is derived from black holes, mainly from active supermassive black holes. This requires a second conceptual leap: the horizon of the black hole undergoes a high temperature and an intense pressure of magnetic fields which cause a blackout and a phase transition (or broken symmetry) when the matter crosses the horizon. The result is a reversal of Maxwell’s laws: a magnetic charge is substituted for the electric charge, and the electric current becomes a tributary of the magnetic current. A third important conceptual leap follows: sterile magnetic neutrinos created inside the black hole would cross the horizon to the outside to constitute dark matter.

Electromagneto-Optical Scanning of the Magnetic Domains Local Areas of Bismuth-Substituted Yttrium Iron Garnets

Magneto-electric properties of the magnetic domains local areas of bismuth-substituted yttrium iron garnet films are investigated. The electromagneto-optical (EMO) scanning method was used in our experiments when probing by laser beam various sites of separate magnetic domains of the film. Registered in our experiments the nonlinear and linear components of EMO effect does not remain to constants at optical scanning of various points of the magnetic domain. I.e. the local EMOE picture from the separate sites of the domain must be more informative than an averaged one in the multidomain case.

Frequency-Diversified Space-Efficient Radiating Surface Using Convolved Electric and Magnetic Currents for Highly Dense Multiband Antenna-Frontend Integration

We propose and investigate a methodology based on convolved electric and magnetic currents for the generation of multi-band responses over a space-shared radiating surface.First,a single wideband antenna operation principle based on inter-leaved dipole and slot modes is studied and analyzed using full-wave simulations followed by a qualitative time domain analysis.Subsequently,a 2×2 dual-band radiating unit is conceived and developed by closely arranging single wideband antennas.In this case,multimode resonances are generated in a lower frequency band by a proper convolving and coupling of the magnetic and electric currents realized in the gaps between the antennas and on the surface of the antennas,respectively.This methodology can be deployed repeatedly to build up a self-scalable topology by reusing the electromagnetically(EM)connected radiating surfaces and gaps be-tween the radiating units.Due to the efficient reuse of the electromagnetic region for the development of multiband radiation,a high aperture-reuse efficiency is achieved.Finally,as a proof of concept,a 2×4 dual-band array operating in Ku-and Ka-bands is devel-oped and fabricated by a linear arrangement of the two developed radiating units.Our measurement results show that the proposed antenna array provides impedance and gain bandwidths of 30%and 25.4%in the Ku-band and 10.65%and 8.52%in the Ka-band,respectively.

Construction of Co_(2)NiO_(4)@MnCo_(2)O_(4.5)nanoparticles with multiple hetero-interfaces for enhanced electromagnetic wave absorption

Nanocomposites with heterogeneous structures and magneto-electric synergistic losses have broad prospects for improving electromagnetic wave(EMW)absorption performance.In this study,we synthesized Co_(2)NiO_(4)@MnCo_(2)O_(4.5)nanoparticles with abundant hetero-interfaces and multiple magnetoelectric loss mechanisms by a facile hydrothermal method.The excess 0.5 oxygen atoms in MnCo_(2)O_(4.5) produce more vacancies and contribute to the enhancement of electrical conductivity.Sequential nanoneedle clusters facilitate multiple reflections and absorption of EMW in the materials,which are accompanied by an abundance of heterogeneous interfaces to improve the dielectric loss.The Co_(2)NiO_(4)@MnCo_(2)O_(4.5)composites showed a minimum reflection loss(RLmin)of30.01 dB and a superior effective absorption bandwidth(EAB)of 6.12 GHz(11.88 GHze18 GHz)at a thickness of 2.00 mm.Computer Simulation Technology(CST)revealed that the obtained particles show very low radar crosssection(RCS)values and almost full coverage angles.The maximum reduction of RCS at vertical incidence reaches 19.98 dB m2.The Co_(2)NiO_(4)@MnCo_(2)O_(4.5)nanoparticles exhibit outstanding radar attenuation properties,which can effectively inhibit the reflection and scattering of EMW.Therefore,the prepared Co_(2)NiO_(4)@MnCo_(2)O_(4.5)absorbers have great application potential in the field of EMW absorption.

Magnetic field-induced strategy for synergistic CI/Ti_(3)C_(2)T_(x)/PVDF multilayer structured composite films with excellent electromagnetic interference shielding performance

Lightweight,scalable,mechanically flexible conductive polymer composite was always desirable for electromagnetic interference(EMI)shielding applications.In this work,we showcased a novel approach to the superior EMI shielding composite materials by orchestrating the multilayered structure and synergistic system.The asymmetric structure with the carbonyl irons(CI)-rich Ti_(3)C_(2)T_(x)/poly(vinylidene fluoride)(PVDF)magneto-electric layer jointly behind the Ti_(3)C_(2)T_(x) nanosheets filled PVDF layer was designed and fabricated with the aid of a facile but efficient magnetic field-induced method and was then hotpressed into a multilayer structured film.Ti_(3)C_(2)T_(x) nanosheets were excluded by CI agglomeration layer in the asymmetric film to form the complete 3D electrical conductive skeletons.Based on this strategy,EMI shielding properties of the asymmetric multilayer structured composite was superior to the homogeneous blend and sandwiched or alternating layered composites.In addition,an increase in CI content in the composite referred to the thickening of CI-rich layers,making it gain the most powerful EMI SE values,i.e.42.8 d B for DCMP20–10 film(20 wt%CI,10 wt%Ti_(3)C_(2)T_(x))at a thickness of 0.4 mm.More importantly,the composite transformed from a reflection type to an absorption dominating EMI shielding material due to the multireflections and magneto-electric synergism in the CI-rich Ti_(3)C_(2)T_(x)/PVDF layers.Meanwhile,the EMI SE of the composites can be adjusted by increase of either theoverall thickness,or the layer numbers of m-DCMP sheets.The thickness specific EMI SE was calculated as 165.25 d B mm^(-1)for 4-sheet composite film,a record high value among the high efficiency polymer-based EMI shielding materials.This method offered an alternative protocol for preferential integration of excellent EMI shielding performance with high mechanical performance in CPC materials.

Study of multiferroic properties of Bi_(2)Fe_(2)WO_(9) ceramic for devices application

The Bi_(2)Fe_(2)WO_(9) ceramic was prepared using a standard solid-state reaction technique.Preliminary analysis of X-ray diffraction pattern revealed the formation of single-phase compound with orthorhombic crystal symmetry.The surface morphology of the material captured using scanning electron microscope(SEM)exhibits formation of a densely packed microstructure.Comprehensive study of dielectric properties showed two anomalies at 200℃and 450℃:first one may be related to magnetic whereas second one may be related to ferroelectric phase transition.The field dependent magnetic study of the material shows the existence of small remnant magnetization(M_(r))of 0.052 emμ/g at room temperature.The existence of magneto-electric(ME)coupling coefficient along with above properties confirms multi-ferroic characteristics of the compound.Selected range temperature and frequency dependent electrical parameters(impedance,modulus,conductivity)of the compound shows that electric properties are correlated to its microstructure.Detailed studies of frequency dependence of ac conductivity suggest that the material obeys Jonscher's universal power law.