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## High-voltage electrophoretic deposition of preferentially oriented films from multiferroic YMn2O5 nanopowders

Brankovic, G.; Brankovic, Z.; Sequinel, T.; Zunic, M.; Vukovic, M.; Tasic, N.; Marinkovic, B. A.; Cilence, M.; Varela, José Arana; Longo, Elson
Tipo: Artigo de Revista Científica Formato: 2065-2068
ENG
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Processing of the YMn2O5 powder is very challenging, since it decomposes to YMnO3 and Mn3O4 at temperatures close to 1180 °C, while samples consolidation commonly demands high temperatures. The main goal of this work is to investigate a possibility to prepare thick films of YMn2O5, since their deposition generally requires significantly lower temperatures. Multiferroic YMn 2O5 was synthesized by the hydrothermal method from Y(CH3COO)3·xH2O, Mn(CH 3COO)2·4H2O and KMnO4 precursors. XRD, FE-SEM and TEM analysis showed that the obtained powder was monophasic, with orthorhombic crystal structure and columnar particle shape with mean diameter and length of around 20 and 50 nm, respectively. The obtained powder was suspended in isopropyl alcohol with addition of appropriate binder and deflocculant. This suspension was used for electrophoretic deposition of YMn2O5 thick films under the high-voltage conditions and electric fields ranging from 250 to 2125 V/cm. The films obtained at 1000 V/cm and higher electric fields showed good adhesion, particle packing, homogeneity and very low porosity. It was shown that the deposition in extremely high electric fields (KC=2125 V/cm) can influence the crystal orientation of the films, resulting in formation of preferentially oriented films. © 2012 Elsevier Ltd and Techna Group S.r.l.

## Mechanosynthesis of the multiferroic cubic spinel Co2MnO4: Influence of the calcination temperature

Santos, Maria Elenice dos; Castro, Alicia; Martinez, Inmaculada; Lisboa Filho, Paulo Noronha; Pena, Octavio
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 7185-7193
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Processo FAPESP: 07/08072-0; Multiferroic materials showing magnetoelectric coupling are required in various technological applications. Many synthetical approaches can be used to improve the magnetic and/or electrical properties, in particular when the materials exhibit cationic valence fluctuations, as in the Co2MnO4 cubic spinel. In this compound, Co and Mn ions are in competition at the tetrahedral and octahedral positions, depending on their various oxidation states. The Co2MnO4 was prepared following two techniques: by a soft chemical route based on a modified polymer precursor method, and by a mechanoactivation route. Both approaches yield polycrystalline powders, but their crystallites sizes and particles morphologies differ as a function of the calcination conditions. The magnetic characterization (ZFC/FC cycles, ordering temperatures, ferromagnetic coercive fields and saturation magnetizations) showed that the synthesis procedure influenced the physical properties of Co2MnO4 mainly through the size of the magnetic domains, which play an important role on the magnetic interactions between the Co/Mn cations. Crown Copyright (C) 2013 Published by Elsevier Ltd and Techna Group S.r.l. All rights reserved.

## Estudo da estrutura local da família RMn2O5 (R=Bi, Tb, Gd, Pr); Local structure study of the family RMn205 (R=Bi, Tb, Gd,Pr)

Gilberto Fernandes Lopes Fabbris
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
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## Study of multiferroic materials; Estudo de materiais multiferroicos

Figueiras, Fábio Gabriel Nazário
ENG
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The present PhD work aims the research and development of materials that exhibit multiferroic properties, in particular having a significant interaction between ferromagnetism and ferroelectricity; either directly within an intrinsic single phase or by combining extrinsic materials, achieving the coupling of properties through mechanic phenomena of the respective magnetostriction and piezoelectricity. These hybrid properties will allow the cross modification of magnetic and electric polarization states by the application of cross external magnetic and/or electric fields, giving way to a vast area for scientific investigation and potential technological applications in a new generation of electronic devices, such as computer memories, signal processing, transducers, sensors, etc. Initial experimental work consisted in chemical synthesis of nano powders oxides by urea pyrolysis method: A series of ceramic bulk composites with potential multiferroic properties comprised: of LuMnO3 with La0.7Sr0.3MnO3 and BaTiO3 with La0.7Ba0.3MnO3; and a series based on the intrinsic multiferroic LuMn1-zO3 phase modified with of Manganese vacancies. The acquisition of a new magnetron RF sputtering deposition system, in the Physics Department of Aveiro University...

## Dielectric study at microwave frequencies of phase transitions in multiferroic ceramics

Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
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Multiferroic ceramic solid solutions between the ferroelectric relaxor Pb(Fe2/3W1/3)O3 (PFW) and "normal" ferroelectric PbTiO3 (PT) - PFW-PT have been synthesized by a modified B-site precursor method and characterized by microwave dielectric measurements. A dielectric dispersion occurring in the frequency range of 100MHz-3GHz and in a broad range of temperatures showed to be a powerful tool to detect electrostrictive and magnetostrictive effects. Anomalies in the temperature dependence of the dielectric parameters (fR (characteristic frequency) and the dielectric strength Δε (characteristic of the dispersion)) have been observed at T N and T C for all samples, indicating that the coupling between the ferroelectric and antiferromagnetic orders occurs "via strain" and confirming the high sensitivity of microwave dielectric measurements to probe weak transitions in bulk ceramics.

## Effect of magnetic ion doping on structural, electric and relaxor properties of Pb (Fe2/3W1/3) O3 multiferroic ceramics

Fraygola,Bárbara; Eiras,José Antônio
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
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Single-phase Pb(Fe2/3W1/3)O3 (PFW) multiferroic ceramics doped with magnetic ions were fabricated using a modified B-site precursor method. Dielectric response was investigated over a wide range of temperature and frequency. Doping did not modify the characteristic temperatures (T C, T N) and the order at ferroelectric phase transition, keeping the relaxor properties. However, the leakage current and resistivity of PFW have been improved with the substitutions: 1 mol% MnO2 addition caused a significant increase in the electric resistivity of PFW ceramics, around 7 orders of magnitude.

## Voltage control of magnetism in multiferroic heterostructures

Liu, Ming; Sun, Nian X.
Fonte: The Royal Society Publishing Publicador: The Royal Society Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Electrical tuning of magnetism is of great fundamental and technical importance for fast, compact and ultra-low power electronic devices. Multiferroics, simultaneously exhibiting ferroelectricity and ferromagnetism, have attracted much interest owing to the capability of controlling magnetism by an electric field through magnetoelectric (ME) coupling. In particular, strong strain-mediated ME interaction observed in layered multiferroic heterostructures makes it practically possible for realizing electrically reconfigurable microwave devices, ultra-low power electronics and magnetoelectric random access memories (MERAMs). In this review, we demonstrate this remarkable E-field manipulation of magnetism in various multiferroic composite systems, aiming at the creation of novel compact, lightweight, energy-efficient and tunable electronic and microwave devices. First of all, tunable microwave devices are demonstrated based on ferrite/ferroelectric and magnetic-metal/ferroelectric composites, showing giant ferromagnetic resonance (FMR) tunability with narrow FMR linewidth. Then, E-field manipulation of magnetoresistance in multiferroic anisotropic magnetoresistance and giant magnetoresistance devices for achieving low-power electronic devices is discussed. Finally...

## Ultra-low-energy straintronics using multiferroic composites

Roy, Kuntal
Tipo: Artigo de Revista Científica
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This paper reviews the recent developments on building nanoelectronics for our future information processing paradigm using multiferroic composites. With appropriate choice of materials, when a tiny voltage of few tens of millivolts is applied across a multiferroic composite, i.e. a piezoelectric layer stain-coupled with a magnetostrictive layer, the piezoelectric layer gets strained and the generated stress in the magnetostrictive layer switches the magnetization direction between its two stable states. We particularly review the switching dynamics of magnetization and calculation of associated metrics like switching delay and energy dissipation. Such voltage-induced magnetization switching mechanism dissipates a minuscule amount of energy of only ~1 attojoule in sub-nanosecond switching delay at room-temperature. The performance metrics for such non-volatile straintronic devices make them very attractive for building not only memory devices but also building logic, so that they can be deemed suitable for computational purposes. Hence, multiferroic straintronics has profound promise of contributing to Beyond Moore's law technology, i.e. of being possible replacement of conventional charge-based electronics, which is reaching its performance limit specifically due to excessive energy dissipation.; Comment: arXiv admin note: text overlap with arXiv:1111.6129

## Dynamics of Multiferroic Domain Wall in Spin-Cycloidal Ferroelectric DyMnO$_{3}$

Kagawa, F.; Mochizuki, M.; Onose, Y.; Murakawa, H.; Kaneko, Y.; Furukawa, N.; Tokura, Y.
Tipo: Artigo de Revista Científica
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We report the dielectric dispersion of the giant magnetocapacitance (GMC) in multiferroic DyMnO$_{3}$ over a wide frequency range. The GMC is found to be attributable not to the softened electromagnon but to the electric-field-driven motion of multiferroic domain wall (DW). In contrast to conventional ferroelectric DWs, the present multiferroic DW motion holds extremely high relaxation rate of $\sim$$10^{7}$ s$^{-1}$ even at low temperatures. This mobile nature as well as the model simulation suggests that the multiferroic DW is not atomically thin as in ferroelectrics but thick, reflecting its magnetic origin.; Comment: 4 pages, 4 figures

## Impurity effects in multiferroic compounds

Datta, Trinanjan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We investigate the effect of impurities in multiferroic materials using an equation of motion approach for the spin dynamics of the host multiferroic compound. We model the impurities as a two-level system and focus on the regime where the impurity spins relax slowly. When the impurity strength is weak the host spins oscillate with no decay and the electric polarization is not affected. However as the impurity strength is increased the host spin components get damped and the electrion polarization is suppressed. Since polarization in multiferroic materials is driven by magnetic ordering we conclude that the presence of impurities is detrimental to multiferroicity.; Comment: 4 pages, 1 figure

## Robust Ferroelectric State in Multiferroic Mn$_{1-x}$Zn$_x$WO$_4$

Chaudhury, R. P.; Ye, F.; Fernandez-Baca, J. A.; Lorenz, B.; Wang, Y. Q.; Sun, Y. Y.; Mook, H. A.; Chu, C. W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We report the remarkably robust ferroelectric state in the multiferroic compound Mn$_{1-x}$Zn$_x$WO$_4$. The substitution of the magnetic Mn$^{2+}$ with nonmagnetic Zn$^{2+}$ reduces the magnetic exchange and provides control of the various magnetic and multiferroic states of MnWO$_4$. Only 5 % of Zn substitution results in a complete suppression of the frustrated collinear (paraelectric) low temperature phase. The helical magnetic and ferroelectric phase develops as the ground state. The multiferroic state is stable up to a high level of substitution of more than 50 %. The magnetic, thermodynamic, and dielectric properties as well as the ferroelectric polarization of single crystals of Mn$_{1-x}$Zn$_x$WO$_4$ are studied for different substitutions up to x=0.5. The magnetic phases have been identified in single crystal neutron scattering experiments. The ferroelectric polarization scales with the neutron intensity of the incommensurate peak of the helical phase.; Comment: 6 pages, 8 figures

## Dynamical magnetoelectric phenomena of multiferroic skyrmions

Mochizuki, Masahito; Seki, Shinichiro
Tipo: Artigo de Revista Científica
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Magnetic skyrmions, vortex-like swirling spin textures characterized by a quantized topological invariant, realized in chiral-lattice magnets are currently attracting intense research interest. In particular, their dynamics under external fields is an issue of vital importance both for fundamental science and for technical application. Whereas observations of magnetic skyrmions had been limited to metallic magnets so far, their realization was discovered also in a chiral-lattice insulating magnet Cu2OSeO3 in 2012. Skyrmions in the insulator turned out to exhibit multiferroic nature with spin-induced ferroelectricity. Strong magnetoelectric coupling between noncollinear skyrmion spins and electric polarizations mediated by relativistic spin-orbit interaction enables us to drive motion and oscillation of magnetic skyrmions by application of electric fields instead of injection of electric currents. Insulating materials also provide an environment suitable for detection of pure spin dynamics through spectroscopic measurements owing to absence of appreciable charge excitations. In this article, we review recent theoretical and experimental studies on multiferroic properties and dynamical magnetoelectric phenomena of magnetic skyrmions in insulators. We argue that multiferroic skyrmions show unique coupled oscillation modes of magnetizations and polarizations...

## Giant Magnetoelastic Effects in BaTiO3-based Extrinsic Multiferroic Hybrids

Gepraegs, Stephan; Opel, Matthias; Goennenwein, Sebastian T. B.; Gross, Rudolf
Tipo: Artigo de Revista Científica
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Extrinsic multiferroic hybrid structures consisting of ferromagnetic and ferroelectric layers elastically coupled to each other are promising due to their robust magnetoelectric effects even at room temperature. For a quantitative analysis of these magnetoelectric effects, a detailed knowledge of the piezoelectric and magnetoelastic behavior of both constituents as well as their mutual elastic coupling is mandatory. We here report on a theoretical and experimental study of the magnetic behavior of BaTiO3-based extrinsic multiferroic structures. An excellent agreement between molecular dynamics simulations and the experiments was found for Fe50Co50/BaTiO3 and Ni/BaTiO3 hybrid structures. This demonstrates that the magnetic behavior of extrinsic multiferroic hybrid structures can be determined by means of ab-initio calculations, allowing for the design of novel multiferroic hybrids.

## Multiferroic materials and magnetoelectric physics: symmetry, entanglement, excitation, and topology

Dong, Shuai; Liu, Jun-Ming; Cheong, Sang-Wook; Ren, Zhifeng
Tipo: Artigo de Revista Científica
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Multiferroics are those materials with more than one ferroic order, and magnetoelectricity refers to the mutual coupling between magnetism and electricity. The discipline of multiferroicity has never been so highly active as that in the first decade of the twenty-first century, and it has become one of the hottest disciplines of condensed matter physics and materials science. A series of milestones and steady progress in the past decade have enabled our understanding of multiferroic physics substantially comprehensive and profound, which is further pushing forward the research frontier of this exciting area. The availability of more multiferroic materials and improved magnetoelectric performance are approaching to make the applications within reach. While seminal review articles covering the major progress before 2010 are available, an updated review addressing the new achievements since that time becomes imperative. In this review, following a concise outline of the basic knowledge of multiferroicity and magnetoelectricity, we summarize the important research activities on multiferroics, especially magnetoelectricity and related physics in the last six years. We consider not only single-phase multiferroics but also multiferroic heterostructures. We address the physical mechanisms regarding magnetoelectric coupling so that the backbone of this divergent discipline can be highlighted. A series of issues on lattice symmetry...

## Interfacial Coupling in Multiferroic-Ferromagnet Heterostructures

Trassin, M.; Clarkson, J. D.; Bowden, S. R.; Liu, Jian; Heron, J. T.; Paull, R. J.; Arenholz, E.; Pierce, D. T.; Unguris, J.
Tipo: Artigo de Revista Científica
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We report local probe investigations of the magnetic interaction between BiFeO3 films and a ferromagnetic Co0.9Fe0.1 layer. Within the constraints of intralayer exchange coupling in the Co0.9Fe0.1, the multiferroic imprint in the ferromagnet results in a collinear arrangement of the local magnetization and the in-plane BiFeO3 ferroelectric polarization. The magnetic anisotropy is uniaxial, and an in-plane effective coupling field of order 10 mT is derived. Measurements as a function of multiferroic layer thickness show that the influence of the multiferroic layer on the magnetic layer becomes negligible for 3 nm thick BiFeO3 films. We ascribe this breakdown in the exchange coupling to a weakening of the antiferromagnetic order in the ultrathin BiFeO3 film based on our X-ray linear dichroism measurements. These observations are consistent with an interfacial exchange coupling between the CoFe moments and a canted antiferromagnetic moment in the BiFeO3.

## Magnetodielectric effect without multiferroic coupling

Catalan, G.
Tipo: Artigo de Revista Científica
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The existence of a magnetodielectric (magnetocapacitance) effect is often used as a test for multiferroic behavior in new material systems. However, strong magnetodielectric effects can also be achieved through a combination of magnetoresistance and the Maxwell-Wagner effect, unrelated to multiferroic coupling. The fact that this resistive magnetocapacitance does not require multiferroic materials may be advantageous for some practical applications. Conversely, it also implies that magnetocapacitance per se is not sufficient to establish multiferroic coupling.; Comment: Submitted to Applied Physics Letters; 13 pages, 3 figures

## Multiferroic properties and magnetic structure of Sm1-xYxMnO3

O'Flynn, D.; Tomy, C. V.; Lees, M. R.; Daoud-Aladine, A.; Balakrishnan, G.
Tipo: Artigo de Revista Científica
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We have successfully induced multiferroic behavior in the A-type antiferromagnet SmMnO3 by the substitution of Y at the Sm site. A magnetic transition develops at 24 K for Sm1-xYxMnO3 (x=0.4,0.5) which is not present in the parent compound. This transition coincides with the onset of electric order, with an electric polarization measured along the c axis. It is proposed that the effect of Y doping is to bring about a subtle distortion of the MnO6 octahedra, causing a magnetic ordering of the Mn3+ moments similar to that reported for the well studied multiferroic TbMnO3. Following on from our previous study on polycrystalline samples, we present measurements of the magnetic and electric properties of single crystal Sm0.6Y0.4MnO3 and Sm0.5Y0.5MnO3. The data are summarized in a phase diagram for each of the principal crystallographic axes for the x=0.5 compound. Powder neutron diffraction experiments on SmMnO3 and Sm0.6Y0.4MnO3 show that the Y substitution causes a change in the Mn-O-Mn bond angle towards the value found for TbMnO3. The magnetic structure of Sm0.6Y0.4MnO3 has been shown to consist of two phases: a sinusoidal ordering of the Mn3+ moments below 50 K and a cycloidal ordering below 27 K. The cycloidal ordering occurs at the same temperature as the previously observed ferroelectric polarization...

## High-pressure cupric oxide: a room-temperature multiferroic

Rocquefelte, Xavier; Schwarz, Karlheinz; Blaha, Peter; Kumar, Sanjeev; Brink, Jeroen van den
Tipo: Artigo de Revista Científica
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Multiferroic materials, in which ferroelectric and magnetic ordering coexist, are of fundamental interest for the development of multi-state memory devices that allow for electrical writing and non-destructive magnetic read-out operation. The great challenge is to create multiferroic materials that operate at room-temperature and have a large ferroelectric polarization P. Cupric oxide, CuO, is promising because of its large P ~ 10^{2} {\mu}C.m^{-2}, but is unfortunately only multiferroic in a temperature range of 20 K, from 210 to 230 K. Here, using a combination of density functional theory and Monte Carlo calculations, we establish that pressure-driven phase competition induces a giant stabilization of the multiferroic phase of CuO, which at 20-40 GPa becomes stable in a domain larger than 300 K, from 0 to T > 300 K. Thus, under high-pressure, CuO is predicted to be a room-temperature multiferroic with large polarization.; Comment: 18 pages, 9 figures

## Recent Progress of Multiferroic Perovskite Manganites

Dong, Shuai; Liu, Jun-Ming
Tipo: Artigo de Revista Científica
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Many multiferroic materials, with various chemical compositions and crystal structures, have been discovered in the past years. Among these multiferroics, some perovskite manganites with ferroelectricity driven by magnetic orders are of particular interest. In these multiferroic perovskite manganites, not only their multiferroic properties are quite prominent, but also the involved physical mechanisms are very plenty and representative. In this Brief Review, we will introduce some recent theoretical and experimental progress on multiferroic manganites.; Comment: 24 pages, 17 figures. A brief review

## Elastic and magnetoelastic relaxation behaviour of multiferroic (ferromagnetic + ferroelectric + ferroelastic) Pb(Fe_0.5Nb_0.5)O_3 perovskite

Carpenter, M. A.; Schiemer, J. A.; Lascu, I.; Harrison, R. J.; Kumar, A.; Katiyar, R. S.; Ortega, N.; Sanchez, D. A.; Salazar Mejia, C.; Schnelle, W.; Echizen, M.; Shinohara, H..; Heap, A. J. F.; Nagaratnam, R.; Dutton, S. E.; Scott, J. F.
Fonte: IOP Science Publicador: IOP Science
Tipo: Article; published version
EN
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This is the final version of the article. It first appeared from IOP Science via http://dx.doi.org/10.1088/0953-8984/27/28/285901; Resonant Ultrasound Spectroscopy has been used to characterise elastic and anelastic anomalies in a polycrystalline sample of multiferroic Pb(Fe_0.5Nb_0.5)O_3 (PFN). Elastic softening begins at ~550 K, which is close to the Burns temperature marking the development of dynamical polar nanoregions. A small increase in acoustic loss at ~425 K coincides with the value of T* reported for polar nanoregions starting to acquire a static or quasistatic component. Softening of the shear modulus by ~30-35% through ~395-320 K, together with a peak in acoustic loss, is due to classical strain/order parameter coupling through the cubic ? tetragonal ? monoclinic transition sequence of ferroelectric/ferroelastic transitions. A plateau of high acoustic loss below ~320 K is due to the mobility under stress of a ferroelastic microstructure but, instead of the typical effects of freezing of twin wall motion at some low temperature, there is a steady decrease in loss and increase in elastic stiffness below ~85 K. This is attributed to freezing of a succession of strain-coupled defects with a range of relaxation times and is consistent with a report in the literature that PFN develops a tweed microstructure over a wide temperature interval. No overt anomaly was observed near the expected N?el point...