Anisotropic and nonlinear magnetodielectric effects in orthoferrite ErFeO3 single crystals.
ABSTRACT: In rare-earth orthoferrites, strongly correlated order parameters have been thoroughly investigated, which aims to find multiple functionalities such as multiferroic or magnetoelectric properties. We have discovered highly anisotropic and nonlinear magnetodielectric effects from detailed measurements of magnetoelectric properties in single-crystalline orthoferrite, ErFeO3. Isothermal dielectric constant varies in shapes and signs depending on the relative orientations between the external electric and magnetic fields, which may be ascribed to the spin-phonon couplings. In addition, a dielectric constant with both electric and magnetic fields along the c axis exhibits two symmetric sharp anomalies, which are closely relevant to the spin-flop transition, below the ordering temperature of Er3+ spins, TEr?=?3.4 K. We speculate that the magnetostriction from the exchange couplings between Er3+ and Fe3+ magnetic moments would be responsible for this relationship between electric and magnetic properties. Our results present significant characteristics of the orthoferrite compounds and offer a crucial guide for exploring suitable materials for magnetoelectric functional applications.
Project description:The manipulation of antiferromagnetic order in magnetoelectric Cr<sub>2</sub>O<sub>3</sub> using electric field has been of great interest due to its potential in low-power electronics. The substantial leakage and low dielectric breakdown observed in twinned Cr<sub>2</sub>O<sub>3</sub> thin films, however, hinders its development in energy efficient spintronics. To compensate, large film thicknesses (250 nm or greater) have been employed at the expense of device scalability. Recently, epitaxial V<sub>2</sub>O<sub>3</sub> thin film electrodes have been used to eliminate twin boundaries and significantly reduce the leakage of 300 nm thick single crystal films. Here we report the electrical endurance and magnetic properties of thin (less than 100 nm) single crystal Cr<sub>2</sub>O<sub>3</sub> films on epitaxial V<sub>2</sub>O<sub>3</sub> buffered Al<sub>2</sub>O<sub>3</sub> (0001) single crystal substrates. The growth of Cr<sub>2</sub>O<sub>3</sub> on isostructural V<sub>2</sub>O<sub>3</sub> thin film electrodes helps eliminate the existence of twin domains in Cr<sub>2</sub>O<sub>3</sub> films, therefore significantly reducing leakage current and increasing dielectric breakdown. 60 nm thick Cr<sub>2</sub>O<sub>3</sub> films show bulk-like resistivity (~?10<sup>12</sup> ? cm) with a breakdown voltage in the range of 150-300 MV/m. Exchange bias measurements of 30 nm thick Cr<sub>2</sub>O<sub>3</sub> display a blocking temperature of?~?285 K while room temperature optical second harmonic generation measurements possess the symmetry consistent with bulk magnetic order.
Project description:Multiferroic composites are promising candidates for magnetic field sensors, next-generation low power memory and spintronic devices, as they exhibit much higher magnetoelectric (ME) coupling and coupled ordering parameters compared to the single-phase multiferroics. Hence, the 3-0 type particulate multiferroic composites having general formula (1 - ?)[PbFe<sub>0.5</sub>Nb<sub>0.5</sub>O<sub>3</sub>]-?[Co<sub>0.6</sub>Zn<sub>0.4</sub>Fe<sub>1.7</sub>Mn<sub>0.3</sub>O<sub>4</sub>] (??=?0.0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, (1 - ?) PFN-?CZFMO) were prepared using a hybrid synthesis technique. Preliminary structural and microstructural analysis were carried out using XRD and FESEM techniques, which suggest the formation of 3-0 type particulate composite without the presence of any impurity phases. The multiferroic behaviour of the composites is studied with polarization versus electric field (P-E) and magnetization versus magnetic field (M-H) characteristics at room temperature. The nature of ME coupling was investigated elaborately by employing the Landau free energy equation along with the magneto-capacitance measurement. This investigation suggests the existence of biquadratic nature of ME coupling (P<sup>2</sup>M<sup>2</sup>). The magneto-electric coupling measurement also suggests that strain mediated domain coupling between the ferroelectric and magnetic ordering is responsible for the magneto-electric behaviour. The obtained value of direct ME coefficient 26.78 mV/cm-Oe for ??=?0.3, found to be higher than the well-known single-phase materials and polycrystalline composites.
Project description:Laminated magnetoelectric composites of Li<sub>0.058</sub>(Na<sub>0.535</sub>K<sub>0.48</sub>)<sub>0.942</sub>NbO<sub>3</sub> (LKNN)/Co<sub>0.6</sub>Zn<sub>0.4</sub>Fe<sub>1.7</sub>Mn<sub>0.3</sub>O<sub>4</sub> (CZFM) prepared by the conventional solid-state sintering method were investigated for their dielectric, magnetic, and magnetoelectric properties. The microstructure of the laminated composites indicates that the LKNN phase and CZFM phase can coexist in the composites. Compared with the particulate magnetoelectric composites, the laminated composites have better piezoelectric and magnetoelectric properties due to their higher resistances and lower leakage currents. The magnetoelectric behaviors lie on the relative mass ratio of LKNN phase and CZFM phase. The laminated composites possess a high Curie temperature (T<sub>C</sub>) of 463?°C, and the largest ME coefficient of 285?mV/cm Oe, which is the highest value for the lead-free bulk ceramic magnetoelectric composites so far.
Project description:The low dielectric constant of the nonpolar polymer poly(1-butene) (PB-1) limits its application as a diaphragm element in energy storage capacitors. In this work, Ba(Zr<sub>0.2</sub>Ti<sub>0.8</sub>)O<sub>3</sub>-coated multiwalled carbon nanotubes (BZT@MWCNTs) were first prepared by using the sol-gel hydrothermal method and then modified with polydopamine (PDA) via noncovalent polymerization. Finally, PB-1 matrix composite films filled with PDA-modified BZT@MWCNTs nanoparticles were fabricated through a solution-casting method. Results indicated that the PDA-modified BZT@MWCNTs had good dispersion and binding force in the PB-1 matrix. These characteristics improved the dielectric and energy storage performances of the films. Specifically, the PDA-modified 10 vol% BZT@ 0.5 vol% MWCNTs/PB-1 composite film exhibited the best dielectric performance. At 1 kHz, the dielectric constant of this film was 25.43, which was 12.7 times that of pure PB-1 films. Moreover, its dielectric loss was 0.0077. Furthermore, under the weak electric field of 210 MV·m<sup>-1</sup>, the highest energy density of the PDA-modified 10 vol% BZT@ 0.5 vol% MWCNTs/PB-1 composite film was 4.57 J·cm<sup>-3</sup>, which was over 3.5 times that of PB-1 film (?1.3 J·cm<sup>-3</sup> at 388 MV·m<sup>-1</sup>).
Project description:In vortex-like spin arrangements, multiple spins can combine into emergent multipole moments. Such multipole moments have broken space-inversion and time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME) activity. Three types of such multipole moments are known: toroidal; monopole; and quadrupole moments. So far, however, the ME activity of these multipole moments has only been established experimentally for the toroidal moment. Here we propose a magnetic square cupola cluster, in which four corner-sharing square-coordinated metal-ligand fragments form a noncoplanar buckled structure, as a promising structural unit that carries an ME-active multipole moment. We substantiate this idea by observing clear magnetodielectric signals associated with an antiferroic ME-active magnetic quadrupole order in the real material Ba(TiO)Cu<sub>4</sub>(PO<sub>4</sub>)<sub>4</sub>. The present result serves as a useful guide for exploring and designing new ME-active materials based on vortex-like spin arrangements.
Project description:A multiferroic composite consisting of single phases of 30 vol.% magnetostrictive ferrite and 70 vol.% relaxor ferroelectric has been synthesized. The ferrite exhibits a diffuse dielectric phase transition (DPT)with the transition temperature varying from 450?K to 600?K and an activation energy of 0.29?eV. Magnetically, it has a soft behavior with 70 emug-1 saturation magnetization and a Curie transition at ~620?K. The relaxor ferroelectric phase on the other hand exhibits two clear DPTs at 390?K-400?K and 150?K-300?K. The composite of these two shows a soft ferromagnetic behavior reminiscent of the ferrite along with 3 DPTs. There is strong coupling between the two orders - magnetostrictive and piezoelectric in the composite. The capacitance decreases by 45% in the presence of magnetic field corresponding to a sensitivity of 0.9% kOe-1, an extremely large value. The magnetoelectric coupling constant is found to be 20.6 mVcm-1Oe-1, a large value for a bulk composite. Microwave band stop filters of different thicknesses made from the composite have resonant frequencies which upshift in the presence of magnetic field indicating a multiferroic behavior with possibility for electric field tuning of resonant frequency.
Project description:The quasi-one-dimensional, chiral crystal structure of Selenium has fascinating implications: we report simultaneous magnetic and ferroelectric order in single crystalline Se microtubes below ≈40 K. This is accompanied by a structural transition involving a partial fragmentation of the infinite chains without losing overall crystalline order. Raman spectral data indicate a coupling of magnons with phonons and electric field, while the dielectric constant shows a strong dependence on magnetic field. Our first-principles theoretical analysis reveals that this unexpected multiferroic behavior originates from Selenium being a weak topological insulator. It thus exhibits stable electronic states at its surface, and magnetism emerges from their spin polarization. Consequently, the broken two-fold rotational symmetry permits switchable polarization along its helical axis. We explain the observed magnetoelectric couplings using a Landau theory based on the coupling of phonons with spin and electric field. Our work opens up a new class of topological surface-multiferroics with chiral bulk structure.
Project description:The mutual control of the electric and magnetic properties of a multiferroic solid is of fundamental and great technological importance. In this article, the synthesis procedure of La<sub>0.2</sub>Pb<sub>0.7</sub>Fe<sub>12</sub>O<sub>19</sub> ceramics was briefly described and the data acquired for the materials characterization is presented. This data article is related to the research article-Acta Mater. 2016, 121, 144 (j.actamat.2016.08.083). Electric polarization hysteresis loop and I-V curve, which help to confirm the ferroelectricity of La<sub>0.2</sub>Pb<sub>0.7</sub>Fe<sub>12</sub>O<sub>19</sub> ceramics, were presented. Strong magnetic polarization data was also presented. The great variation of the dielectric constants along with the magnetic field has been presented which helped to demonstrat the giant magnetocapacitance of La<sub>0.2</sub>Pb<sub>0.7</sub>Fe<sub>12</sub>O<sub>19</sub>. All the datasets were collected at room temperature. Large ferroelectricity, strong magnetism and colossal magneto-capacitance effect have been all realized in one single phase La<sub>0.2</sub>Pb<sub>0.7</sub>Fe<sub>12</sub>O<sub>19</sub> at room temperature.
Project description:Pure cubic phase ultra-small ?-NaYF<sub>4</sub>:4 % Eu<sup>3+</sup> colloidal nanoparticles were synthesized by thermal decomposition reaction using three various capping ligands, i.e., oleic acid, trioctylphosphine oxide, and hexadecylamine. To expose as many Eu<sup>3+</sup> ions as possible to interactions with the surface-bounded ligands, the nanoparticles were fabricated to have the diameters below 10 nm. The geometrical structure and properties of surface ligands needed for qualitative estimation of their influence on spectroscopic features of the investigated Eu<sup>3+</sup> doped nanoparticles were obtained from DFT quantum-chemical calculations. Significant changes of luminescence spectra shapes and luminescence lifetime values were observed upon changes in the local chemical environment. We show that the ratio <i>R</i> = <sup>5</sup><i>D</i><sub>0</sub> ? <sup>7</sup><i>F</i><sub>1</sub>/<sup>5</sup><i>D</i><sub>0</sub> ? <sup>7</sup><i>F</i><sub>2</sub> of the intensities of the forced electric dipole (<i>J</i> = 2) and magnetic dipole (<i>J</i> = 1) transitions in the synthesized Eu<sup>3+</sup> doped nanoparticles is highly sensitive to the type of ligand present on the nanoparticle surface. Similarly, <sup>5</sup><i>D</i><sub>0</sub> luminescence lifetimes are found to be sensitive to the refractive index, and also to the dielectric constant of ligands used during the synthesis to coat nanoparticles surface. We argue that the photophysical and electro-optical properties of colloidal Eu<sup>3+</sup> doped inorganic nanoparticles show hyper-sensitive response to the chemical surroundings in the close vicinity of the nanoparticle itself. The behavior of both steady-state luminescence and its kinetics demonstrates the potential suitability of the studied nanoparticles for constructing self-referencing optical nano-sensors.
Project description:In magnetoelectric materials, magnetic and dielectric/ferroelectric properties couple to each other. This coupling could enable lower power consumption and new functionalities in devices such as sensors, memories and transducers, since voltages instead of electric currents are sensing and controlling the magnetic state. We explore a different approach to magnetoelectric coupling in which we use the magnetic spin state instead of the more traditional ferro or antiferromagnetic order to couple to electric properties. In our molecular compound, magnetic field induces a spin crossover from the S?=?1 to the S?=?2 state of Mn3+, which in turn generates molecular distortions and electric dipoles. These dipoles couple to the magnetic easy axis, and form different polar, antipolar and paraelectric phases vs magnetic field and temperature. Spin crossover compounds are a large class of materials where the spin state can modify the structure, and here we demonstrate that this is a route to magnetoelectric coupling.