Symposium C
Recent Advances in Multiferroic and Magnetoelectric Materials and Applications

ABSTRACTS

C:KL  Coupling Magnetism to Electricity In Multiferroic Heterostructures
R. RAMESH, Department of Physics and Department of Materials Science and Engineering, University of California, Berkeley, CA, USA
 
Complex perovskite oxides exhibit a rich spectrum of functional responses, including magnetism, ferroelectricity, highly correlated electron behavior, superconductivity, etc. The basic materials physics of such materials provide the ideal playground for interdisciplinary scientific exploration. Among the large number of materials systems, there exists a small set of materials which exhibit multiple order parameters; these are known as multiferroics. Our work so far has clearly demonstrated the possibility of reversible, electric field switching and control of the state and direction of magnetization. I will present our results to date.


Session C-1 - Theory and Modeling of Single Phase and Composite Multiferroics

C-1:IL03  New Multiferroics at Interfaces of Conducting Oxides
J.M. RONDINELLI, D. PUGGIONI, Northwestern University, Evanston, Illinois, USA

The metallic features in materials, which provide low-resistance for electrical conduction, lead to effective screening of local electric dipole moments and frequently centric (inversion symmetric) crystal structures. Despite this contraindication, noncentrosymmetric metals (NCSM) lacking inversion were proposed more than fifty years ago with some examples discovered later. Here, I describe a design framework to alleviate such property disparities and accelerate NCSM discovery at the interfaces of conducting nonpolar oxides: The primary ingredient relies on the removal of inversion symmetry through displacements of atoms whose electronic degrees of freedom are decoupled from the states at the Fermi level. Density functional theory calculations validate the crystal-chemistry strategy, and predict a polar-NCS perovskite ruthenate superlattice to be metallic and robust to spin-orbit interactions. Then, I discuss how to design new multiferroics by interfacing the NCSM materials platform with “dull” dielectrics, using a LiOsO3/LiNbO3 superlattice as an example. It exhibits strong coupling between the magnetic and ferroelectric order. These results support a new route towards high-temperature multiferroics, i.e., driving nonmagnetic NCSM into correlated insulating magnetic states.


C-1:IL04  The Path Matters: The Key to Magnetization Reversal by Electric Field
J. INIGUEZ, Luxembourg Institute of Science and Technology, Esch-sur-Alzette, Luxembourg

Controlling (and hopefully reversing) the room-temperature magnetization of a material by application of an electric field remains a great challenge for workers on multiferroic oxides. In this talk I will summarize several recent works that illustrate a variety of alternative routes to achieve such a goal. I will describe theoretical predictions suggesting that it is possible to take advantage of novel couplings, between a variety of magnetic and structural order parameters, to achieve magnetization reversal in the so-called hybrid improper ferroelectric compounds, such as La2NiMnO6- and BiFeO3-based superlattices. I will also discuss in which particular conditions such a mgnetization reversal can be achieved in classic multiferroic BiFeO3. My talk will emphasize a feature that is commmon to all these cases, namely, the critical importance of controlling the switching path. Works done in collaboration with many colleagues, primarily from L. Bellaiche's (U Arkansas), P. Ghosez's (U Liege) and R. Ramesh's (UC Berkeley) groups.


C-1:IL05  Metallo-ferroelectricity, Multiferroicity and Magnetoelectricity in Layered Perovskites
V. FIORENTINI, A. FILIPPETTI, J. INIGUEZ*, F. RICCI, P. DELUGAS, M. SCARROZZA, M.B. MACCIONI, Dipartimento di Fisica, Università di Cagliari, and CNR-IOM, Cagliari, Italy ; *LIST, Esch-sur-Alzette, Luxembourg

Just as their standard counterpart, layered perovskites are emerging as a very interesting playground in the field of multiferroicity and related phenomena. Specifically I will discuss members of the family A(n)X(n)O(3n+2), with A trivalent and X tetravalent. Our main showcase is the first known native ferroelectric metal, Bi5Ti5O17 (n=5 in the family), which exhibits coexisting native ferroelectricity and metallicity, including a residual ferroelectricity-induced field in a finite system. Time permitting, I will address the n=4 insulating case: the highlights there are the weak ferromagnet La2Mn2O7 with its anomalously large linear magnetoeletric coupling, and V-doped La2Ti2O7, a ferroelectric ferromagnet exhibiting quintessential magnetoelectricity, i.e. magnetization inversion upon electrical inversion of the polarization.


C-1:IL06  Magnetoelectric Multipoles in Multiferroics and Complex Oxides
M. FECHNER, ETH Zürich, Switzerland

The linear magnetoelectric effect couples magnetic and electric excitations within a material. A consequence of this coupling is the formation of parity and time reversal odd magnetic multipolar order[1-3]. Magnetic hedgehogs, toroidal and magnetic quadrupole moments represent this order and the topic of this talk. First we present a scheme to calculate such multipole moments within the framework of first-principles calculations[3] and then discuss their manifestations in two cupper oxide materials. In CuO measurements revealed a toroidal order[4] within the antiferromagnetic phase. Our calculations revealed a spin asymmetry around Cu as the source of this order, which is created by a strong hybridization of neighboring Cu-d and O-p orbitals. In contrast in HgBa2CuO4, the multipolar order inferred from experimental measurements[5] originate from a ‘’dynamic’’ scenario. Here the coupling of spin and phononic system creates a quasi-static multipolar order in absence of static magnetic order.
[1] D. I. Khomskii, Nature Commun. 5, 1 (2014). [2] M. Fechner, et. al., Phys. Rev. B. 89, 184415 (2014). [3] N. A. Spaldin, et. al., Phys. Rev. B. 88, 094429 (2013). [4] V. Scagnoli, et. al., Science 332, 696 (2011). [5] S. W. Lovesey and D. D. Khalyavin, arXiv cond-mat.str-el, (2015).


C-1:IL07  Impact of Magnetic Configuration and Local Electric Dipoles on Electronic Properties of BiFeO3 with Spatial Bond Length Modulation
D. RICINSKI, Tokyo Institute of Technology, Yokohama, Japan

In this work, first-principles calculations under the Density Functional Theory are used to explore unconventional BiFeO3 (BFO) structures with spatial modulation of Bi-Bi bond lengths. The modulation was obtained by promoting formation of mixed large and small c/a ratio regions in quasi-tetragonal BFO supercells, through elastic constraints as well as by introduction of point and planar defects such as oxygen vacancies. The impact of the magnetic configuration (including multiple spin and oxidation state of Fe) coupled to local crystallographic features of supercells on their electronic properties are examined in view of emerging optoelectronic and energy applications of BFO.


C-1:L08  Composites for Novel Magnetic Properties
E.A. BURGESS, A.P. HIBBINS, J.R. SAMBLES, S. HORSLEY, C. GALLAGHER, C. McKEEVER, EPSRC Centre for Doctoral Training in Metamaterials (XM2), Dept.of Physics and Astronomy / Dept.of Engineering, University of Exeter, UK

Carbonyl iron powders (CIP), produced by thermal decomposition of iron pentacarbonyl, have been widely used in composite form to produce microwave materials for many decades. They are often utilised in preference to conventional ferrite powders because they offer a higher frequency response. Their properties are attributed to the electromagnetic resonances of their unique structure: “onion-like”, micron-sized particles, involving thin, concentric spherical shells of alternating magnetic (iron) and non-magnetic layers. However the mechanisms dictating their properties has not been widely discussed in the literature. It is the focus of this study to deepen the understanding of the physical properties, resonances, interactions and processes that govern the magnetic resonance within these structures. With this information, we are designing and fabricating simplified analogies to the CIP particles, which are then embedded in a polymer matrix to create novel materials, which are subsequently characterised.

 
Session C-2 - Non-oxide, Organic-inorganic and 5-d Oxide Multiferroics

C-2:L01  Multiferroic Properties of Organic-inorganic Hybrid Compounds
T.M. PALSTRA, M. KAMMINGA, Zernike Institute for Advanced Materials, University of Groningen, The Netherlands

We have investigated organic-inorganic hybrids that combine electronic functionality of the perovskite structures and structural flexibility of metal-organic framework compounds. The chemistry of inorganic materials offers a wide range of band gaps or bandwidths with high carrier density and mobility, magnetic interactions, ferroelectric transitions and thermal stability. On the other hand, organic solids provide nearly unlimited flexibility in structural diversity, good polarizability and they can also be made conductive. The aim of investigating these hybrid materials is to utilize the chemical diversity of the organic moieties with the physical properties of the inorganic moieties to produce useful combinations or even completely new phenomena. We illustrate the opportunities by several examples: 1. Combining ferroelectricity and (anti-)ferromagnetism in Cu- and Mn-based hybrids, 2. The chemical diversity for the perovskite hybrids for solar cells, and 3. Modulating the 1-dimensional magnetism in NiCl3-based hybrids. We show that in all examples the properties of the inorganic block can be controlled by using different organic moieties, without the need for substitutions or dopants.


C-2:IL02  Multiferroic Behavior Triggered by a Spin-state Transition
V. ZAPF, S. CHIKARA, S. LIN, B. SCOTT, C. BATISTA, N. SMYTHE, Los Alamos National Lab., Los Alamos, NM, USA

Multiferroic behavior traditionally refers to the coexistence of magnetic and electric long range order. Here we describe how a spin-state transition, rather than ferromagnetism, can trigger ferroelectricity. Spin-state transitions are inherently strongly coupled to the lattice as they involve a rearrangement of the orbital occupancy, and therefore the ionic size and bonding. In metal-organics with dense magnetic ions, spin-state crossovers are not purely local ionic phenomena, but rather can induce structural phase transitions. Here we describe our observation of significant electric polarization induced at a magnetic field-induced phase transition from a low-spin to high-spin state in a Mn complex.


C-2:IL03  Multiferroics and Magnetoelectric Effects in Metal-organic Frameworks
YOUNG SUN, YING TIAN, WEI WANG, LIQIN YAN, YISHENG CHAI, Institute of Physics, Chinese Academy of Sciences, Beijing, China

The hybrid metal-organic frameworks (MOFs) that combine both merits of inorganic and organic materials represent a new family of multifunctional materials. In this talk, we report the multiferroics and magnetoelectric effects in a series of MOFs with a perovskite-like structure. Single-crystal samples of MOFs were prepared by solvothermal methods. These MOFs show a magnetic ordering at 5-20 K, depending on the magnetic ions (Cu2+, Mn2+, Co2+ or Fe2+). Meanwhile, they also exhibit a ferroelectric/antiferroelectric transition between 160-270 K. Both direct and converse ME effects have been observed in these MOFs. Especially, the Fe-based MOF exhibits the most interesting behaviors, such as resonant quantum tunneling of magnetization, electric control of magnetism, and resonant quantum ME effect. The possible origin of the multiferroics and ME effects in MOFs is discussed in terms of the role of hydrogen bonding and magnetoelastic coupling.


C-2:L04  Infrared Phonon Modes and Intrinsic Dielectric Response of Magnetodielectric La2CoMnO6
R.L. MOREIRA, R. PANIAGO, R.M. ALMEIDA, Belo Horizonte, MG, Brazil; R.X. SILVA, C.W.A. PASCHOAL, São Luís, MA, Brazil

Double perovskites of the chemical formula RE2MeMnO6 (RE = rare earth or Y; Me = Ni or Co) are attractive because their interesting physical properties such as multiferroicity and electrical-magnetic couplings. In particular, La2CoMnO6 (LCMO) shows a relatively high Curie temperature (Tc ̴ 230K), Colossal Dielectric Constant (CDC) and strong magnetodielectric effects. In this work, the infrared (IR) reflectivity spectra of LCMO ceramics obtained from a modified Pechini’s method were investigated aiming to elucidate the role of the synthesis conditions on the structural and dynamic behaviors of the materials. X-ray diffraction and XPS analyses confirmed that the samples synthesized from 700 to 1000 °C crystallized into a double perovskite structure of the P21/n space group, with ordered (Mn4+/Co2+) cations. Dispersion analysis by a four-parameter semi-quantum model revealed the most intense polar modes that describe the reflectivity spectra. The phonon modes are weakly coupled with low dielectric losses. The extrapolated low-frequency IR (10 GHz) dielectric constant and quality factor matched well with the relaxed radio-frequency values, demonstrating that the reported CDC effect in LCMO has pure extrinsic origin. (Work partially supported by CNPq, FAPEMA, FAPEMIG and CAPES.)


Session C-3 - Advances in Materials Synthesis and Processing

C-3:IL01  DNA-assisted Self-assembly of Multiferroic Nanocomposites and Studies on Magneto-electric Interactions
G. SRINIVASAN1, G. SREENIVASULU1, M. PANDA2, F.A. CHAVEZ2, 1Department of Physics, Oakland University, Rochester, MI, USA; 2Department of Chemistry, Oakland University, Rochester, MI, USA

Multiferroic composites with ferroelectric and ferromagnetic phases have attracted considerable attention in recent years for studies on strain mediated magneto-electric (ME) interactions. Nanocomposites are of interests due to a large surface-to-volume ratio. We recently synthesized core-shell nickel ferrite (NFO) and barium titanate (BTO) core-shell nanoparticulate composites by click-reaction aided chemical self-assembly by creating covalent attachments between the particles. This technique, however, created nanocomposites that are limited in size due to low coupling efficiency for the click reaction. Here we discuss DNA-assisted self-assembly, a process that is reversible and promising for synthesis of superstructures of the composite with nm-periodicity. We used NFO (10-200 nm) and BTO (50-600 nm) particles to synthesize core-shell structures. Mixing BTO and NFO particles, possessing complementary DNA sequences, resulted in formation of nanocomposites held together by DNA hybridization. The core-shell architecture was observed by SEM and scanning microwave microscopy. Magneto-dielectric measurements indicated strong ME coupling between NFO and BTO in the composites.- Research was supported by a grant from the Army Research office.


C-3:IL02  Epitaxial Growth of BiFeO3 Thin Films by RF and Dual Ion Beam Sputtering
S. NAKASHIMA, M. SHIMIZU, H. FUJISAWA, University of Hyogo, Himeji, Hyogo, Japan

Recently, new functionalities of BiFeO3 (BFO) such as photovoltaic effect and resistive switching including switching of diode characteristics induced by polarization switching, in which BFO acted as a semiconductor, have been reported. However, BFO deposition by conventional sputtering process has been very difficult except for off-axis sputtering. In this study, we overcame some difficulties and successfully prepared epitaxial BFO thin films by the dual-ion-beam sputtering (Dual-IBS) and the conventional rf planar magnetron processes (RFSPT). High quality epitaxial BFO thin films with various film thicknesses were successfully grown on SrTiO3 (001) and SrRuO3-buffered SrTiO3 (001) by Dual-IBS and RFSPT. The domain structure can be controlled by vicinal direction of STO substrates, and the single-domain structured BFO thin films were grown on vicinal STO (001) along <110>. The single-domain BFO thin films with thicknesses from 100 to 1000 nm showed well-saturated square-shaped ferroelectric D-E hysteresis loops with a remanent polarization (Pr) of 60 µC/cm2 at R.T. At the conference, we will discuss details of structural, ferroelectric and electrical properties of the BFO thin films, and epitaxial growth of tetragonal-like BFO thin films on LaAlO3 substrates.


C-3:IL05  Spray Pyrolysis to Process Thin Films of Multiferroic Materials
A.E. LÓPEZ-LÓPEZ, L. ROLDÁN, J. ORTIZ-LANDEROS, C. GOMEZ-YANEZ, Department of Metallurgical and Materials Eng., ESIQIE, National Polytechnic Institute, Zacatenco, Mexico city, Mexico

Great efforts have been done to test cheap synthesis methods to produce thin films with enough quality to gain the interest of the electronic industry. Currently in the industrial world, expensive methods such as sputtering, molecular beam epitaxy or pulsed laser deposition are used to produce microdevices. The smallest devices are composed by films thinner than 100 nanometers which are dense, epitaxial and defect free. Then, methods such as spray pyrolysis have to be able to produce films with these characteristics. Moreover, in the case of multiferroic films, the ferroelectric performance should be good enough to show values of remnant polarization as well as magnetic properties similar to those accomplished using physical deposition methods. Spray pyrolysis can be seen as an atmospheric-pressure version of CVD, therefore, avoiding vacuum pumps and expensive mass flow controllers, the cost can be reduced greatly. Spray pyrolysis is a promising technic because it involves as many variables to play with as CVD does, except pressure, in order to produce the films with the required characteristics. In the present work, the progress in multiferroic films, mainly BiFeO3 based-systems, produced by spray pyrolysis will be discussed as well as their relevant properties.


C-3:L09  Correlation of Magnetoelectric Coupling in Multiferroic BaTiO3-BiFeO3 Superlattices and Composite Thin Films with Ordering of Oxygen-related Defects
M. LORENZ1, V. LAZENKA2, G. WAGNER3, P. SCHWINKENDORF1, M.J. VAN BEAL4, A. VANTOMME2, K. TEMST2, O. OECKLER3, M. GRUNDMANN1, 1Institut für Experimentelle Physik II, Universität Leipzig, Leipzig, Germany; 2Instituut voor Kern- en Stralingsfysica, KU Leuven, Leuven, Belgium; 3Institut für Mineralogie, Kristallographie und Materialwissenschaft, Universität Leipzig, Leipzig, Germany; 4Laboratorium voor Vaste-Stoffysica en Magnetisme, KU Leuven, Leuven, Belgium 

In comparison to single-phase multiferroics, composites are promising to show high magnetoelectric coupling. We have conducted systematic investigations of multiferroic composite thin films and multilayers built from BaTiO3 and BiFeO3 [1,2,3]. A direct longitudinal AC method yields very high magnetoelectric voltage coefficients up to 43 and 49 V/cmOe at 300 K, for chemically homogeneous 67% BaTiO3 - 33% BiFeO3 composite films and (BaTiO3-BiFeO3)×15 multilayers, respectively. These values are close to the highest reported and exceed that of a BiFeO3 reference film (4.2 V/cmOe) remarkably [2,3]. We found clear correlation of ME coefficients to the density of oxygen vacancies as controlled by the oxygen partial pressure during PLD growth, and related structural defects such as strain and mosaizity [2]. Detailed STEM and SAED microstructural investigations revealed antiphase rotations of the oxygen octahedra and an oxygen vacancy superstructure in the superlattices and composite films, respectively, which are additional correlated defect structures of multiferroic magnetoelectrics.
[1] M. Lorenz et al., J. Phys. D: Appl. Phys. 47, 135303 (2014); [2] M. Lorenz et al., Appl. Phys. Lett. 106, 012905 (2015); [3] V. Lazenka et al., Appl. Phys. Lett. 106, 082904 (2015).


C-3:L10  Heterostructured Ceramic Materials Based on PZTN-CFO Compounds
P. GALIZIA, C. CAPIANI, C. GALASSI, CNR-ISTEC, Faenza, Italy

Solid state process has been used to control the microstructure and to improve the densification and the interphase boundaries cohesion of heterostructured ceramics. In this work, synthesis, milling and sintering of the powders mixture, were optimized to achieve a proper dispersion of the magnetic phase (CoFe2O4) in highly densified ferroelectric matrix (Nb-doped PZT). The aim is that to increase the mechanical coupling and the percolation threshold by increasing the densification and reducing the magnetic grain size. The optimized microstructure showed a fully dense microstructure characterized by a bi-modal cobalt ferrite grain size distribution in the nanoscale. SEM-EDXS and XRD analysis have been used to study the microstructure after heat treatment and a simple equation – to quantify the PbO losses – has been deducted from the XRD analysis.


Session C-4 - Magnetoelectric Characterization and Electric Field Control of Magnetization

C-4:IL01  Voltage Control of Magnetic Vortex States in Ni Discs Using Ferroelectric Substrates
M. GHIDINI1, 2, R. MANSELL3, X. MOYA1, B. NAIR1, S. FAROKHIPOOR1, D. PESQUERA1, F. MACCHEROZZI4, C.H.W. BARNES3, R.P. COWBURN3, S.S. DHESI4, N.D. MATHUR1, 1Department of Materials Science, University of Cambridge, Cambridge, UK; 2DiFeST, University of Parma, Parma, Italy; 3Cavendish Laboratory, University of Cambridge, Cambridge, UK; 4Diamond Light Source, Chilton, Didcot, Oxfordshire, UK

We investigate manipulation of magnetic vortex states in Ni dots (diameter 0.5-2 microns) via voltage-induced strain from ferroelectric substrates of BTO and PMN-PT. Vortex chirality is monitored using XMCD-PEEM (photoemission electron microscopy, with contrast from X ray magnetic circular dichroism) to construct vector maps of in-plane magnetization. Vortex polarity is monitored using MFM (magnetic force microscopy) to obtain maps representing out-of-plane magnetization. Independent electrical switching of polarity and chirality is explored.


C-4:IL02  Spintronics with Ferroelectrics
E.Y. TSYMBAL, Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, USA

Ferroelectric materials are characterized by a spontaneous electric polarization switchable by an applied electric field. If such a ferroelectric is interfaced with a metal it modifies the electronic properties of the metal near the interface through effects of charge screening and interface bonding. For thin metallic ferromagnets the effects of polarization from an adjacent ferroelectric may be sizable and involve not only electronic but also spin degrees of freedom. Thus, ferroelectric materials may be employed in spintronics to control the spin-dependent properties including the interface magnetization, the interface magnetic order, the interface magnetic anisotropy, and the spin-dependent transmission across the interface. Furthermore, ferroelectric films can now be made thin enough to allow measurable electron tunneling while maintaining a stable and switchable polarization. Modeling and experiments show that ferroelectric tunnel junctions allow the control of the spin-polarization of the tunneling current. This talk will overview our recent research efforts in this field and discuss underlying physical principles associated the effects of ferroelectricity on magnetism and spin transport.


C-4:IL03  Electrical Control of Large Magnetization Reversal in a Helimagnet
KEE HOON KIM, CeNSCMR, Department of Physics and Astronomy, Seoul National University, Seoul, Korea

Despite its technical and fundamental importance, reversal of macroscopic magnetization by an electric field (E) has rarely been achieved and remains a considerable challenge. Here, we report the strong modulation and large reversal of magnetization (M) by E in a multiferroic Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 crystal at zero magnetic field, in which a transverse conical spin state exhibits a remanent M and electric polarization below ~150 K. Upon sweeping E through the range of ±2 MV m-1, M varied quasi-linearly in the range of ±2 μB per f.u., resulting in the reversal of M. Moreover, the remanent M exhibited non-volatile changes of ±0.15 μB per f.u., depending on the history of the applied electric fields. The strong modulation and non-volatile two-states of M at zero magnetic field were observable up to ~150 K. Nuclear magnetic resonance measurements provided microscopic evidence that the electric field and the magnetic field play equivalent roles in modulating the volume of magnetic domains. Our results suggest that soft ferrimagnetism with small magnetic anisotropy and the related transverse conical state are key ingredients to achieve the giant converse magnetoelectric effect, indicating a novel pathway toward achieving large magnetization reversal by electric fields at fairly high temperatures [1].
[1] Y. S. Chai et al., Nature comm. 5, 4208 (2014); Sae Hwan Chun et al., Phys. Rev. Lett. 108, 177201 (2012); ibid, 104, 037204 (2010);


C-4:IL04  Mesoscale Interfacial Dynamics in Magnetoelectric Nanocomposites
D. VIEHLAND, J.F. LI, Dept. Materials Science and Engineering, Virginia Tech, Blacksburg, VA, USA 

Both heterostructural and vertically integrated two phase ME epitaxial thin layers have been fabricated by various deposition methods. With regards to vertically integrated nanostructures, our investigations have shown various phase architectures of self-assembled BiFeO3-CoFe2O4 (BFO-CFO) thin films on differently oriented SrTiO3 (STO) and Pb(Mg1/3Nb2/3)O3-xat%PbTiO3 (PMN-x%PT) substrates [40]. CFO forms segregated square, stripe, and triangular nanopillars embedded in a coherent BFO matrix on (001)-, (110)- and (111)-oriented substrates, respectively. The results suggest a way to effectively control the magnetic anisotropy in patterned ferromagnetic oxide arrays with tunable shape, aspect ratio, and elastic strain conditions of the nanostructures. These two phase layers, and of CFO heterostructures, on PMN-x%PT have pronounced magnetoelectric effects. In particular, large E-field tunable magnetic anisotropies were found. For PMN-x%PT substrate compositions near a morphotropic phase boundary (MPB), both volatile and non-volatile effects have been reported, which can be tuned with substrate composition. This opens up the unique possibility to develop giant ME materials with unique multi-state reconfigurable properties, with and without memory.


C-4:IL05  Observation and Control of Spin Chirality in Room-temperature Magnetoelectric Hexaferrites
T. KIMURA1, H. UEDA1, H. NAKAJIMA1, T. USUI1, Y. HIRAOKA1, Y. WAKABAYASHI1, Y. TANAKA2, 1Osaka University, Toyonaka, Osaka, Japan; 2RIKEN SPring-8 Center, Japan

Resonant x-ray scattering is known as powerful technique to study symmetry breakings by orderings of various multipole moments, such as spin and orbital. This technique is recently applied to verify symmetry breakings by the development of the chirality which is determined as an asymmetry of the object upon its mirroring in crystallography and magnetism, and which plays a crucial role in various materials’ functionality such as piezoelectricity and multiferroicity. With the help of the resonant x-ray scattering technique using circularly-polarized and highly-focused x-ray beam, we investigated the observation and the control of spin chirality in magnetoelectrics such as hexaferrite systems showing a room-temperature magnetoelectric effect.


C-4:IL06  Room Temperature Magnetoelectric Effect in Novel Oxides
J.A. EIRAS, Federal University of São Carlos, São Carlos, SP, Brazil

In the last decades, innumerous experimental and theoretical studies have been devoted to predict and describe mechanisms involved in the magnetoelectric effect (ME) and to improve its magnitude, to enable an electric field control of ferromagnetism or a magnetic field control of the electric polarization. Large scale applications requires materials with enhanced ME coupling at room temperature. One direction to investigate multiferroic magnetoelectrics is to explore polar (FE and pyroelectric) crystals hosting magnetic elements, responsible for the establishment of ferromagnetic or AF orders. Advances in processing methods of complex multiferroic oxides have attracted increasing attention in recent years due to the possibilities to improve the ME coupling at room temperature and to get a depth inside in new and fundamental physics of the involved mechanisms. In this presentation will be presented and discussed recent experimental results (dielectric, pyroelectric, magnetic and elastic results) from complex oxides (lead based and lead free), which present room temperature ME coupling. The origin of the ferroelectricity, and magnetic ordering and ME coupling in these materials will be highlighted.


C-4:L07  Enhanced Magnetoelectric Coupling in Multiferroics from First-principles
S. LISENKOV, University of South Florida, Tampa, FL, USA

Multiferroics have attracted an unprecedented attention in the recent years owing to their potential to exhibit magnetoelectric coupling. Such coupling could open the ways to innovative applications such as four-state logic in a single device, magnetoelectric random access memories, electrically controlled exchange bias applications. We propose an unusual route to a robust enhancement of magnetoelectric coupling via thermally mediated mechanism. Such mechanism couples magnetization to the electric field (polarization to the magnetic induction) indirectly by taking advantage of pyromagnetic and electrocaloric (pyroelectric and magnetocaloric) properties of the material. This approach was tested in both direct and indirect first-principles-based simulations and revealed that a significant enhancement of magnetoelectric coupling could be achieved. In particular, we predict a four order of magnitude enhancement of magnetoelectric coupling in the most celebrated multiferroic BiFeO3. From thermodynamics point of view, the thermally mediated magnetoelectric effect is quantified by an isentropic rather than isothermal magnetoelectric response.


C-4:L08  Observation of Magnetoelectric Effect in Organic Ferromagnetic and Ferroelectric Liquid Crystals
RUI TAMURA, K. SUZUKI, Kyoto University, Kyoto, Japan; Y. UCHIDA, Osaka University, Osaka, Japan

Since 2004 we have reported the preparation and magnetic properties of chiral rod-like all-organic liquid crystalline (LC) radical compounds with a stable chiral cyclic nitroxide unit in the mesogen core, which can show a variety of chiral and achiral LC phases over a wide temperature range [1]. Consequently, we could discover a unique magnetic phenomenon, referred to as "positive magneto-LC effects", a generation of spin glass-like inhomogeneous ferromagnetic interactions (the average spin-spin interaction constant, J > 0) induced by low magnetic fields in the various LC phases [2].
Here I talk about the following electric and magnetic properties which these chiral nitroxide radical compounds exhibited in the chiral smectic C (SmC*) phase; 1) ferroelectricity, 2) positive magneto-LC effects and 3) magnetoelectric effect in the ferromagnetic and ferroelectric LC phase at high temperatures [3].
[1] N. Ikuma et al, Angew. Chem. Int. Ed., 2004, 43, 3677; N. Ikuma et al, Adv. Mater., 2006, 18, 477.
[2] Y. Uchida et al, J. Am. Chem. Soc., 2010, 132, 9746; K. Suzuki et al, J. Mater. Chem., 2012, 22, 6799.
[3] K. Suzuki et al, Soft Matter, 2013, 4687; R. Tamura et al, Advances in Organic Crystal Chemistry: Comprehensive Review 2015, Springer, chap. 35, p 689.



C-4:L09  Anomalous Magnetoresistivity in Co-doped ZnO with Varying Bottom Gate Voltage
MIYEON CHEON1, YONG CHAN CHO2, CHUL-HONG PARK3, SE YOUNG JEONG4,5, 1Crystal Bank Research Institute, Pusan National University, Miryang, Korea; 2Korea Research Institute of Standards and Science, Daejeon, Korea; 3Dept. of Physics Education, Pusan National University, Busan, Korea; 4Dept. of Cogno-Mechatronics Engineering, Pusan National University, Miryang, Korea; 5Dept. of Optics and Mechatronics Engineering, Pusan National University, Miryang, Korea

The dependence of the magnetoresistivity in Co-doped ZnO on gate voltages at 5, 7 and 10 K was investigated. The Co-doped ZnO sample was hydrogenated weakly in short time, so the Co-H-Co complexes are expected to be formed independently as magnetic unit. The magnetoresistivity at 5, 7 and 10 K showed very different behaviors. With deceasing gate voltage from 20.0 V to -20.0 V, the resistivity increased and then decreased at 5 K, while it increased monotonically at 7 K and 10 K. At 7 K, the resistivity oscillates between two curves with the positive gate voltage near the zero magnetic field. At 10 K, the resistivity oscillates between two curves within the whole range of the magnetic field and the region where the resistivity oscillates increases as the magnetic field increases. The magnetoresistivity changed discontinuously and oscillated between two curves at particular magnetic fields and at the particular gate voltages. These behaviors are evidences that the Co-H-Co complexes exist independently and give quantized resistance depending on gate voltages. In this study, we intend to prove that individual Co-H-Co complex is the magnetic unit in molecular form.

 
Session C-5 - Domain Walls and Dynamics of Multiferroics

C-5:IL01  Domain Walls and Magnetism in BiFeO3 – Redux
L.W. MARTIN, Department of Materials Science and Engineering, University of California, Berkeley and Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

We revisit our understanding of BiFeO3 with attention to new insights about the role of domain walls and strain in the evolution of magnetism. We demonstrate pathways to achieve ordered arrays of 180° stripe nanodomains in (110)-oriented BiFeO3 films. Such 180° stripe domains with {11-2} domain walls are observed in films < 32 nm thick to compensate for large depolarization fields, but relax to 71° ferroelastic domains as the thickness increases and elastic energy builds. Additional studies of Co0.9Fe0.1/BiFeO3 heterostructures reveal exchange bias and exchange enhancement in heterostructures based-on BiFeO3 with 180° domain walls and an absence of exchange bias in heterostructures based-on BiFeO3 with 71° domain walls; suggesting that the 180° domain walls could be the possible source for pinned uncompensated spins that give rise to exchange bias. X-ray magnetic circular dichroism studies of samples controlled to have each type of domain wall variant find that films with 109° and 180° domain walls have larger magnetization than those with primarily 71° domain walls. Finally we explore the role of strain on the evolution of the antiferromagnetic axis in BiFeO3 and demonstrate the potential to tune this direction across as wide angular space.


C-5:IL02  Spiral Magnets in Thin Film Form
B. NOHEDA, J.A. HEUVER, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands; S. FAROKHIPOOR, Device Materials group, University of Cambridge, Cambridge, UK; C.J.M. DAUMONT, University of Tours, Tours cedex, France

TbMnO3 and CoCr2O4 are two very different materials but they both show low temperature ferroelectricity induced by spiral magnetic ordering and, thus, both show strong magnetoelectric coupling.  TbMnO3 is an orthorhombic perovskite with a collinear antiferromagnetic transition at 43K and the spin spiral (ferroelectric) transition at 28K. CoCr2O4 is a normal cubic spinel showing net magnetic moment (an antiferrimagnetic phase) below 93K and a conical spin spiral (ferrielectric) transition below 26 K.  In this talk we will discuss the effects of strain and epitaxy in these two materials when grown by pulsed laser deposition with atomic control. 


C-5:IL03  Scrutinizing Electronic Excitations of Multiferroics by Resonant Raman Scattering
M.C. WEBER, M. GUENNOU, J. KREISEL, Luxembourg Institute of Science and Technology (LIST), Department Materials Research and Technology, Belvaux, Luxembourg

Solid knowledge of the electronic band structure of materials is a cornerstone of modern technology. In functional dielectrics and multiferroics, traditionally seen and used as insulating materials, electronic structures have been much less explored than in semiconductors. However, today, they gain importance with the growing interest for interactions of ferroic materials with light, in the context of unique photovoltaic or photoelectric properties. In this study, we demonstrate how resonance Raman spectroscopy enables to probe electronic levels of the model multiferroic BiFeO3. Using twelve different excitation wavelengths ranging from the blue (442 nm = 2.8 eV) to the near infrared (785 nm = 1.6 eV), we show that both the first- and second-order Raman signatures of the crystals show resonance phenomena that can be assigned to the direct and indirect band-gaps, and oxygen electronic defect levels. Temperature-dependent measurements provide the first experimental indication that the reported strong variation of the optical band-gap in BFO originates from a shrinking of the indirect electronic gap. More generally, our study suggests that Raman scattering at various wavelengths offers a powerful tool for the investigation of electronic excitations in multiferroic functional oxides.


C-5:L04  Broadband Dielectric Studies of Cobalt Ferrite and Nb-doped Lead Zirconium Titanate Multiferroic Composites
R. GRIGALAITIS1, A. SAKANAS1, J. BANYS1, C.E. CIOMAGA2, L. MITOSERIU2, 1Department of Radiophysics, Faculty of Physics, Vilnius University, Vilnius, Lithuania; 2Faculty of Physics, University “Al. I. Cuza” Iasi, Romania

The most interesting multiferroic materials at the moment are so-called two-phase multiferroic composites due to the possibility to realize the “product property” referring to effects present in the composites but not in the individual phases. Lead zirconate titanate PbZr xTi1−xO3 is the well known ferroelectric perovskite with excellent electromechanical properties while cobalt ferrite CoFe2O4 exhibit good ferromagnetic and magnetostrictive properties. CF-PZTN composite ceramics with CF ratio of 10%, 20 % and 30% were prepared were prepared in situ by citrate–nitrate combustion by using PZTN-based template powders as described in [2]. Various devices and broadband dielectric spectroscopy methods were used in experiments to cover the wide range of temperatures and frequencies, spanning from 100 K to 500 K and from 20 Hz up to 50 GHz. The obtained results show the slight shift of the peak of dielectric permittivity toward higher temperatures with the increase of CF amount. At room temperature the dielectric behaviour for all compositions satisfies the “sum property” indicating the decrease of the dielectric permittivity with the increase of CF ratio. The types of dielectric dispersions and their main properties will be analyzed in the presentation.

 
Session C-6 - New Effects

C-6:IL01  Room-temperature Ferroelectricity in Atomically Thin 2D CuInP2S6
LU YOU1, FUCAI LIU1, KYLE L. SEYLER2, XIAODONG XU2, ZHENG LIU1, JUNLING WANG1, 1School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore; 2Department of Physics, University of Washington, Seattle, Washington, USA

Ferroelectricity has been extensively studied in three-dimensional (3D) perovskite oxides, such as PbTiO3 and BiFeO3, for applications in electronic and optoelectronic devices. However, epitaxial growth of high-quality films requires the careful selection of substrates with small lattice mismatch. In addition, dangling bonds and defects at the interface drastically deteriorate the electronic coupling between ferroelectric and graphene like 2D materials, due to the complex interface reconstruction and defect chemistry. The groundbreaking work on graphene has triggered an intense search for other 2D materials with intriguing physical properties. However, ferroelectricity has so far remained elusive in the 2D material library. Currently the reported critical thickness for ferroelectricity in layered materials is relatively large, far from the ultrathin limit. We report here the experimental observation of room-temperature ferroelectricity in 2D CuInP2S6 (CIPS) with a transition temperature of ~320 K. Switchable polarization is observed in atomically thin CIPS of ~4 nm, while piezoelectricity is demonstrated in flakes only two atomic layers thick. To demonstrate the potential of this 2D ferroelectric material, we prepare a van der Waals (vdW) ferroelectric diode formed by CIPS/Si heterostructure, which shows good memory behavior with on/off ratio of ~100. The addition of ferroelectricity to the 2D family opens up possibilities for numerous novel applications, including sensors, actuators, non-volatile memory devices, and various vdW heterostructures based on 2D ferroelectricity.


C-6:L03  Temperature Dependent Polarization Reversal Mechanism in (Bi1/2Na1/2)TiO3-based Relaxor Ceramics
J. GLAUM, J. DANIELS, M. HOFFMAN, School of Materials Science and Engineering, UNSW Australia, NSW, Australia; H. SIMONS, Department of Physics, Technical University of Denmark, Kgs. Lyngby, Denmark; M. ACOSTA, Institute of Materials Science, Ceramics Group, Technische Universität Darmstadt, Germany

The (Bi,Na)TiO3-xBaTiO3 piezoceramics is close to the morphotropic phase boundary and exhibits a pseudo-cubic structure in the unpoled state. However, if an electric field is applied it shows strong hysteretic behavior, as expected for polar materials. Electric field application can induce a ferroelectric phase which, depending on composition and temperature, remains or vanishes after electric field is removed. The characteristics of these ceramics are described as relaxor-like and are explained by the formation and disappearance of the domain structure. With increasing temperature, the ferroelectric phase becomes unstable and polarization reversal occurs through a depoling – re-poling process. Depoling can be triggered by small electric fields of reverse polarity for temperatures below the ferroelectric-relaxor transition temperature, TF-R. For T > TF-R the ferroelectric phase vanishes before zero electric field is reached and the phase transition becomes reversible. This transitional behavior has been studied using dielectric and piezoelectric characterization techniques as well as neutron and synchrotron diffraction. The relationship between macroscopic properties and structure will be discussed.


Session C-7 - Devices and Applications

C-7:IL02  Multiferroic and Magnetoelectric Nanocomposites for Data Processing
W. KLEEMANN, H. WENDE, Universität Duisburg-Essen, Duisburg, Germany; P. BORISOV, West Virginia University, Morgantown, USA; C. SCHMITZ-ANTONIAK, FZ Jülich, Germany; L. HENRICHS, University of Leeds, UK

Switching of magnetism with electric fields and magnetic control of electric polarization are challenging tasks for magnetoelectric materials. Layered composite realizations for data storage have been considered. First, we discuss 2-2 composites based on magnetoelectric chromia films (Cr2O3), which allow electric switching of the magnetization of epitaxially grown ultrathin ferromagnetic Co/Pt/Co trilayers via interfacial exchange coupling. Our patented [1] magneto-electric random access memory (MERAM) concept will be presented. Second, PLD grown 1-2 composites of cobalt ferrite (CoFe2O4) nanopillars are shown to yield a shear stress-induced polarization pattern of its BaTiO3 embedding material in a transverse magnetic field [2]. Data storage applications will be discussed. Third, ceramic 0-2 composites of ferrimagnetic-ferroelectric Bi(Fe,Co)O3 nanoclusters embedded in K_0.5Bi_0.5TiO_3 films reveal giant linear magneto-electric response, M = αE with α ≈ 10-5 s/m [3]. They are candidates for electrically addressable nanodot mass memory devices.
[1] A. Hochstrat, X. Chen, P. Borisov, W. Kleemann, US Pat.7,719,883 B2 (2010); [2] C. Schmitz-Antoniak et al, Nat. Comm. 4, 2051 (2013); [3] L.F. Henrichs et al, Advan. Funct. Mater. (subm.)


C-7:L04  Permanent Ferroelectric Retention in BiFeO3 Mesocrystal
YING-HUI HSIEH1, FEI XUE2, TIANNAN YANG2, YEN-CHIN HUANG3, YI-CHUN CHEN3, CHUN-GANG DUAN4, LONG-QING CHEN2, QING HE5, YING-HAO CHU1,6, 1Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan; 2Department of Materials and Engineering, Pennsylvania State University, University Park, PA, USA; 3Department of Physics, National Cheng Kung University, Tainan, Taiwan; 4Key Lab of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai, China; 5Department of Physics, Durham University, Durham, UK; 6Institute of Physics, Academia Sinica, Taipei, Taiwan

Non-volatile electronic devices based on multiferroic have triggered new possibilities to outperform other devices for practical applications. However, the ferroelectric reliability issues, such as imprint, retention, and fatigue, have yet be solved prior to realizing a practical device. In this study, the ferroelectric retention failure has been solved with a new approach. Everlasting ferroelectric retention in heteroepitaxially constrained multiferroic mesocrystals is reported. Studied by scanning probe microscopy and supported via phase field simulation, the key to this success is to prevent the crystal structure from ferroelastic deformation, which is strongly related to the spontaneous polarization switching.


C-7:IL06  Voltage-controlled Exchange Bias in Lithographically Patterned Heterostructures
C. BINEK, W. ECHTENKAMP, X. HE, M. STREET, A. MAHMOOD, J. WANG, K. BELASHCHENKO, P. DOWBEN, Department of Physics & Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, USA

Voltage-controlled exchange bias (EB) enables dissipationless control of interface magnetic states with major implications for spintronic applications such as ultra-low power non-volatile memory and logic devices. Controlling magnetism at thin-film interfaces in the absence of electric currents is a key challenge. A promising route utilizes voltage-switchable interface or boundary magnetization of antiferromagnetic (AF) magnetoelectrics. Quantum mechanical exchange coupling between a ferromagnetic thin film and the boundary magnetization of a magnetoelectric antiferromagnet enables voltage-controlled EB. Voltage-controlled thermally assisted and isothermal switching of perpendicular EB has been demonstrated in heterostructures of the bulk AF magnetoelectric Cr2O3 (chromia) and perpendicular anisotropic ferromagnetic CoPt and CoPd films. Recently, transfer of these pioneering results to the rather challenging all thin film geometry made promising progress. I will present our latest results on voltage-controlled EB in all thin film geometry and lithographically patterned devices.
We acknowledge financial support from C-SPIN, one of the six SRC STARnet Centers, sponsored by MARCO, DARPA and SRC and CNFD an SRC-NRI Center, and by the NSF through the Nebraska MRSEC (DMR-1420645).


C-7:IL07  Multiferroic Technology for Advanced Magnetic Data Storage
M.M. VOPSON, University of Portsmouth, Faculty of Science, SEES, Portsmouth, UK; S. LEPADATU, T. MERCER, University of Central Lancashire, School of Computing, Engineering and Physical Sciences, Preston, UK; M. SPREITZER, Institute Jožef Stefan, Ljubljana, Slovenia

Ultra high-density magnetic data storage of 1Tb per square inch requires magnetic grains typically < 5 nm diameter. To avoid entering super-paramagnetic phase, thermal stability of such magnetic nano-grain demands materials with very large magneto-crystalline anisotropy, which makes the data write process almost impossible, even when Heat Assisted Magnetic Recording (HAMR) technology is deployed. We propose an alternative method of strengthening the thermal stability of the magnetic nano-grains via magneto-electric coupling between the magnetic medium and a piezo-ferroelectric substrate. Using Stoner-Wohlfarth single domain model applied to a magnetic nano-grain we show that the correct tuning of the multiferroic coupling can increase the effective magneto-crystalline anisotropy of the magnetic grains making them stable beyond the super-paramagnetic limit. However, the effective magnetic anisotropy can also be lowered or even switched off during the write process by simply altering the applied voltage to the substrate. Based on these effects, we propose two magnetic data storage protocols, one of which could potentially replace HAMR technology, with both schemes promising unprecedented increases in the data storage areal density beyond the super-paramagnetic size limit.

 
Poster Presentations

C:P05  Technology and Properties of PMN–PT–ferrite Multiferroic Ceramic Composite Materials
R. SKULSKI, D. BOCHENEK, P. NIEMIEC, A. CHROBAK, University of Silesia, Faculty of Computer Science and Materials Science, Institute of Technology and Mechatronics, Sosnowiec, Poland

Investigated by us multiferroic ceramic composite materials consist of two components i.e. ferroelecttric/relaxor one and ferrimagnetic one. The solid solution PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) was used as a ferroelectric/relaxor component while the nickel-zinc ferrite Ni0.64Zn0.36Fe2O4 was used as the magnetic component. PbMg1/3Nb2/3O3 (PMN) is known as a model ferroelectric relaxor with perovskite-type structure but for practical applications solid solution PMN-PT is used more frequently. For x<0.25 PMN-PT has a rhombohedral structure while compositions with x>0.34 have tetragonal structure. For 0.25


C:P08  Ferromagnetic and Ferroelectric Properties of Bi0.95La0.05Fe0.99Ti0.01O3 Nano Ceramics Sintered by the Two-step Method
Y.H. TIAN, Q.Y. FU, D.X. ZHOU, Z.P. ZHENG, W. LUO, YUNXIANG HU, School of optical and electronic information, Huazhong University of Science and Technology, Wuhan, China

To study the effect of grain size on the ferromagnetic, dielectric and structure properties of BiFeO3-based ceramic, Bi0.95La0.05Fe0.99Ti0.01O3 ceramic were successfully synthesized by a modified two step sintering (TSS) method. In the Rietveld refinement, good agreement between the observed and calculated pattern was observed. The grain size of a high-density (>94%) Bi0.95La0.05Fe0.99Ti0.01O3 ceramic produced by the TSS was ~ 350 nm, while the grain size of those formed by conventional sintering method was ~1um. The dielectric response of these samples was analyzed in the frequency range of 100 Hz–10 MHz, and it was found that the dielectric properties were improved by TSS method. Moreover, ferromagnetization of nano ceramic increased by 20 percentages.


C:P09  A Two-step Method Preparation of Core-shell CoFe2O4@ BaTiO3 Multiferroic Composites
L. ZHOU, DONGXIANG ZHOU, Q.Y. FU, Y.X. HU, Z.P. ZHENG, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, PR China

The CoFe2O4@BaTiO3 core-shell multiferroic composites were successfully prepared using a two-step hydrolysis-hydrothermal method with an amount of cationic surfactant added during the hydrolysis procedure. Compared to the particulated samples, the leakage intensity of the core-shell sample reduced two orders of magnitude and the percolation threshold of ferromagnetic phase increased to 0.38. The core-shell sample exhibited strong magnetic-electric (ME) coupling and magnetic-dielectric (MD) effects which induced by the interface of negative magnetostrictive and piezoelectric phase. The further research indicated that the ME and MD effects were originated from the enhancements of rough interface scattering and acoustic phonon scattering when the external magnetic field was applied.


C:P11  The Basic Properties of the Ferroelectromagnetic Composites Based on the Ferrite and PZT-type Powders 
D. BOCHENEK, P. NIEMIEC, R. SKULSKI, University of Silesia, Faculty of Computer Science and Material Science, Institute of Technology and Mechatronics, Sosnowiec, Poland

In this paper a ferroelectric–ferromagnetic composites based on a doped PZT-type and ferrite powders were presented. Ferroelectric powder (in amount of 85.0 wt-%) was based on multicomponent PZT-type materials:
i) Pb(Zr0.51Ti0.49)O3+0.2%at.Bi2O3+0.03%at.Nb2O5+0.06%at.MnO2, 
ii) Pb0.84Ba0.16(Zr0.54Ti0.46)O3+1.0%at.Nb2O5,
while nickel–zinc ferrite Ni1–xZnxFe2O4 (in amount of 15.0 wt-%) served as the magnetic component of the composite samples. The synthesis of the ferroelectric–ferromagnetic composite’s powders was performed by solid state method, while final densification of the synthesized powders was achieved using free sintering method. Conducted basic tests indicate that obtained ferroelectromagnetic ceramic composites (PZT-ferrite type) exhibit good properties giving the possibility to use them to construct magnetoelectric transducers.


C:P13  Effect of Complexing Agent Content on the Formation of Magnesium Ferrite Nanoparticles via Wet Chemical Method
L. SRISOMBAT, J. NONKUMWONG, S. ANANTA, Department of Chemistry, and Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand

Magnesium ferrite (MgFe2O4) compound is an important member of the spinel magnetic materials which can offer the possibility to modify the magnetoelectric coupling phenomena in multiferroic composites. It has been known that complexing agent is one of the important factors for the formation of MgFe2O4 via wet chemical method. Thus, in this work, the effect of complexing agent (ethanolamine) content on the formation of MgFe2O4 nanoparticles was investigated. Magnetic inducibility by permanent magnet was first examined and phase formation of magnetic inducible products was then characterized by X-ray diffraction technique. Morphological evolution, chemical composition and magnetic properties of these nanoparticles were characterized by employing a combination of scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy and vibrating sample magnetometry techniques. The results showed that pure phase of stoichiometric MgFe2O4 nanoparticles with cluster size around 150 nm was obtained after using 120 and 240 mmol of ethanolamine. The maximum magnetization was detected at 120 mmol ethanolamine.


C:P14  Synthesis and Characterization of Soft Magnetic Nanocomposite in Fe2O3-Al System by Solid State Reaction
CHUNGHYO LEE, Mokpo National University, Muan, South Korea

Mechanical alloying (MA) based on solid state reaction at room temperature has been recognized as one of the noble techniques in synthesizing metastable crystalline, amorphous phases and nano-structured alloys. Recently, metal oxide/metal nanocomposites have been received increased attention because of their unique mechanical, electrical and magnetic properties. As is well known, oxide magnetic materials are not only commercial permanent magnets, but are also used for soft magnets in high frequency applications. However, the magnetic properties of oxide materials are far below those obtained in metallic alloys because of their low saturation magnetization. In this work, we studied the magnetic nanocomposite formation by MA a mixture of Fe2O3-Al powders. The change in magnetization and coercivity also reflects the details of the solid‐state reduction process of hematite by pure metal of Al during MA. Also, we report the results of a study of the structure and magnetic properties of nanocomposite compacts prepared by spark plasma sintering (SPS).
Acknowledgements: This work is financially supported by the Ministry of Knowledge Economy (MKE) of Korea.


C:P16  Electromagnetic Interference Shielding Response and Photocatalytic Activity of Polyaniline Coated Fe3O4@TiO2 Core-shell Particles
SO-YONG PARK, JIN-SEUNG JUNG, Department of Chemistry, Gangneung-Wonju National University, Gangneung, South Korea

The increased development and use of electronic devices have led to a new kind of pollution known as electromagnetic interference(EMI). The interference effect leads to not only malfunction of electronic devices but also serious issues such as the human diseases like leukemia, miscarriages, and breast cancer. Many researchers have investigated efficient shieding methods to reduce EMI. In this study, a facile and efficient approach for the fabrication of polyaniline coated Fe3O4@TiO2 particles possessing a good core-shell structure has been demonstrated. EMI shieding effectiveness of the nanocomposite with different weight ratio between Fe3O4@TiO2 nanoparticles and polyaniline were investigated at room temperature and the measurement of EMI shielding effectiveness was carried out in a frequency range of 1-12GHz. The photocatalytic experiment is demonstrated by utilizing the oxidation reaction of famous organic dyes with the core-shell Fe3O4@Tio2 nanostructure.


C:P17  Influence of Mg:Fe Ratio on Chemical Composition of MgFe2O4 Nanoparticles Synthesized by Hydrothermal Method
J. NONKUMWONG, L. SRISOMBAT, S. ANANTA, Department of Chemistry, and Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand

Spinel magnesium ferrite (MgFe2O4) is one of the soft magnetic materials which can be utilized as ferro/ferrimagnetic phase in multiferroic composites for sensors and memory devices. It is well-documented that stoichiometric MgFe2O4 is difficult to achieve via typical solid-state reaction approach. To overcome this problem, several techniques including hydrothermal have been introduced for the preparation of stoichiometric MgFe2O4. However, so far, no reports on the role of Mg:Fe ratio on chemical compositions of MgFe2O4 nanoparticles derived from hydrothermal are available. Thus, in this work, the precursors with various Mg:Fe ratios were employed for the production of MgFe2O4 nanoparticles by hydrothermal method. The chemical compositions of final products were investigated by energy-dispersive X-ray spectroscopy along with phase, morphology and magnetic properties by X-ray diffraction, scanning electron spectroscopy and vibrating sample magnetometry, respectively. The results showed that stoichiometric spinel MgFe2O4 nanoparticles with particle size around 160 nm were successfully obtained by using the precursors with Mg:Fe ratio as 1.5:1. Ferromagnetic and ferroelectric loop observations indicate the simultaneity of ferromagnetic and ferroelectric properties of the materials.


C:P21  Enhanced Photon Absorption and Photocurrent Generation by Implementing a Hexagonal LuMnO3-LuFeO3 Multiferroic Bi-layer Structure
HYEON HAN, HYUN M. JANG, Department of Materials Science and Engineering, and Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea

Ferroelectric photovoltaics (FPVs) are being extensively studied owing to their anomalous high photo-voltages, coupled with reversibly switchable photocurrents. However, FPVs suffer from their extremely low photocurrents, which is primarily due to their wide bandgaps. Herein, we present a bi-layer ferroelectric photovoltaic device that is composed of hexagonal LuMnO3 (h-LMO) and LuFeO3 (h-LFO) thin films having narrow bandgaps for remarkably improved FPV responses. A small lattice mismatch (~0.5%) between h-LMO and h-LFO layers enables us to implement an advantageous multi-layer structure, and the band structure of the hexagonal bi-layer device exhibits favorable energy alignment for the charge migration, especially hole extraction. Moreover, the broadened absorption spectrum caused by two different narrow band gaps (1.5 eV for h-LMO, 2.0 eV for h-LFO) leads to enhanced photon absorption and photocurrent generation over a wide photon-energy range. We will show that the power conversion efficiency of this bi-layer solar cell is a few orders higher than those of classical ferroelectric photovoltaics such as pure BiFeO3 and PZT. The present work demonstrates the feasibility of a new method to design optimal ferroelectric solar cells and other functional-device applications.


C:HP22 Electromechanical Properties of Sr and Nb Co-doped Bi0.5Na0.5TiO3-BaZrO3 Ceramics
ALI HUSSAIN, RIZWAN AHMED MALIK, ADNAN MAQBOOL JAE HONG LEE, MYONG HO KIM, School of Advanced Materials Engineering, Changwon National University, Gyeongnam 641-773, Republic of Korea

Lead-free Sr and Nb co-doped Bi0.5Na0.5TiO3-BaZrO3 ceramics of chemical compositions [0.95Bi0.5Na0.5Ti1-xNbxO3-0.05Ba1-ySryZrO3] abbreviated as BNTN-BSZ were prepared by a conventional solid state reaction method and their structural and electromechanical were studied as function of different Sr and Nb content. A single phase perovskite structure without any evidence of secondary phase was observed for all BNTN-BSZ ceramics. The dielectric response of the both poled and unpoled samples show that the maximum dielectric constant decreased and the dielectric maximum temperature (Tm) shifted towards lower temperature with increasing amount of Sr and Nb content. In addition, inclusion of Sr and Nb into BNT-BZ ceramic decreased both remnant and maximum polarization and changed the loop shape from square to a slim type similar to that of the relaxor ferroelectrics. The field induced strain response of BNTN-BSZ ceramics increases from 0.10% for x, y = 0 to 0.25% for x, y = 0.01, at an applied field of 7 kV/mm. The corresponding dynamic piezoelectric coefficient (Smax/Emax = 357 pm/V) was observed for the x, y = 0.01 composition.
 

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