Symposium FD
Recent Achievements in Multiferroic and Magnetoelectric Materials


FD-1:L03  HP/HT Synthesis and Characterization of Bi2CuMnO6, a RT Longe-range Ordered Magnetic Perovskite
C. COPPI, D. Delmonte, R. Cabassi, E. Gilioli, Institute of Materials for Electronics and Magnetism (IMEM), CNR, Parma, Italy; F. Mezzadri, Department of Chemical Sciences, Life and Environmental Sustainability, University of Parma, Parma, Italy; F. Cugini, M. Solzi, Department of Mathematical, Physical and Computer Sciences, University of Parma, Parma, Italy

Multiferroic materials (MF) exhibit the coexistence of at least magnetic (M) and ferroelectric (FE) orders in a single phase. Strong constraints are necessary to stabilize both FE and M behaviour i.e. specific symmetry rules and electrical/magnetic properties. Most of the proper MF materials, in which magnetism and FE are induced by cations at different crystallographic sites, own perovskite structure. Thanks to its excellent tolerance to chemical and structural distortions, it is possible to explore several ionic substitutions, thus tuning the MF properties. Particularly, the insertion of Bi(III) or Pb(II) ion at the A site, due to 6s2 lone pair, can polarize bonds with neighbouring oxygens and determine space-symmetry breaking, while transition metals with partially filled d-shells at the B sites can induce M order. High Pressure/High Temperature (HP/HT) techniques demonstrate to be a powerful tool to metastabilize complex MF perovskites like Bi2FeMnO6, Pb2FeMoO6 or Bi2FeCrO6. This work reports successful HP/HT syntheses of Bi2CuMnO6, a promising ferrimagnetic MF at RT. By exploring different HP/HT synthesis conditions we find the stability region of the perovskite. Then, we report electrical and magnetic characterizations, highlighting mutual properties like magnetoresistance.

FD-1:IL04  Magneto-ionics in Transition Metal Nitrides and its Potential for Artificial Synapses
Z. Tan1, J. de Rojas1, S. Martins1, A. Nicolenco1, J.L. Costa-Krämer2, A. Quintana3, E. Menéndez1, J. Sort1, 4, 1Departament de Física, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain; 2IMN-Instituto de Micro y Nanotecnología (CNM-CSIC), Tres Cantos, Madrid, Spain; 3Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Barcelona, Spain; 4Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain

Magneto-ionics refers to voltage-driven changes in the magnetic properties of materials as a result of electric-field-induced ion transport. In most systems, magneto-ionics relies on controlled migration of oxygen, hydrogen or lithium ions. Here, I will show that voltage-driven transport of nitrogen ions (i.e., nitrogen magneto-ionics) can be triggered at room temperature in transition metal nitride (CoN, FeN) films via liquid electrolyte gating [1,2]. Nitrogen magneto-ionics can induce reversible ON-OFF transitions of ferromagnetic states at faster rates and lower threshold voltages than oxygen magneto-ionics. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. Remarkably, in contrast to oxygen magneto-ionics, nitrogen transport occurs uniformly creating a plane-wave-like migration front, without assistance of diffusion channels, which is interesting for the implementation of multi-stack memory devices. Furthermore, I will show that nitrogen magneto-ionics can be used to emulate some important neuromorphic functionalities. In particular, by cumulative effects of DC and pulsed voltage actuation (at frequencies in the range 1 – 100 Hz), learning, memory retention, forgetting and self-learning by maturity (with zero energy consumption) can be mimicked by proper adjustment of the CoN film thickness and the pulse frequency. Sub-1s nitrogen magneto-ionics can be achieved by decreasing the CoN film thickness down to 25 nm. The interplay between the high ion speeds in thin CoN films and the pulse frequency results in a trade-off between generation (voltage ON) and partial depletion or recovery (voltage OFF) of ferromagnetism, giving rise to a controllable ion accumulation effect at the interface between the films and the electrolyte [3]. From a hardware viewpoint, this effect can serve as a logical function for the device to decide between self-learning or forgetting emulation, at will, without any additional electric voltage input (i.e., with no power consumption). This constitutes a novel approach to emulate some specific neural functionalities (e.g., learning under deep sleep), not easily achievable using other classes materials currently employed for neuromorphic computing applications.
[1] J. de Rojas, A. Quintana, A. Lopeandía, J. Salguero, B. Muñiz, F. Ibrahim, M. Chshiev, A. Nicolenco, M. O. Liedke, M. Butterling, A. Wagner, V. Sireus, L. Abad, C. J. Jensen, K. Liu, J. Nogués, J. L. Costa-Krämer, E. Menéndez, J. Sort, Nat. Commun. 11 (2020) 5871.
[2] J. de Rojas, J. Salguero, F. Ibrahim, M. Chshiev, A. Quintana, A. Lopeandia, M. O. Liedke, M. Butterling, E. Hirschmann, A. Wagner, L. Abad, J. L. Costa-Krämer, E. Menéndez, J. Sort, ACS Appl. Mater. Interfaces 13 (2021) 30826–30834.
[3] Z. Tan, J. de Rojas, S. Martins, A. Lopeandía, L. Abad, A. Quintana, J. Salguero, M. Cialone, J. Herrero-Martín, J. Meersschaut, A. Vantomme, J. L. Costa-Krämer, J. Sort, E. Menéndez, submitted (2021).

FD-1:IL05  Structural Transitions between Metastable Phases in Bismuth-containing Perovskite Multiferroics
A.N. Salak1, J.P. Cardoso1, D. Delmonte2, E. Gilioli2, V.V. Shvartsman3, D.D. Khalyavin4, 1Department of Materials and Ceramics Engineering and CICECO - Aveiro Institute of Materials, University of Aveiro, Aveiro, Portugal; 2Institute of Materials for Electronics and Magnetism, Parma, Italy; 3Institute for Materials Science and CENIDE - Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Essen, Germany; 4ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, UK

Perovskite multiferroics derived from bismuth ferrite attract great attention in respect to both fundamental research and practical application. While the conventional preparation methods are generally applicable to obtain bulk polycrystalline samples with the entire range of the Bi-site substitutions, wide ranges of Fe-site substitutions are possible under high pressure synthesis only. The phenomenon of annealing-stimulated irreversible transformations of the high-pressure stabilized phases (conversion polymorphism) has recently been recognized as a new and promising approach to produce novel multiferroic materials. It has been shown that conversion is the only way to stabilize some of the polymorphs in a bulk form and these polymorphs exhibit unique properties. There are strong indications that conversion polymorphism is a general phenomenon, which has been overlooked in many metastable oxygen octahedral compositions obtained so far. We report on reversible and irreversible transformations between metastable phases of the Bi-containing perovskite solid solutions BiFeO3-BiScO3, BiFeO3- BiZn0.5Ti0.5O3 and BiMg0.5Ti0.5O3-BiZn0.5Ti0.5O3 below their decomposition temperature. New perovskite polymorphs with interesting combinations of ferroic orders are compared and discussed.

FD-2:IL02  Switchable Spin Springs at Oxide Interfaces
K. Dörr, M.M. Koch, L. Bergmann, A.D. Rata, A. Herklotz, Institute of Physics, MLU Halle-Wittenberg, Halle, Germany

In complex transition metal oxides, magnetic anisotropy and magnetic interactions (exchange, Dzyaloshinskii Moriya (DM)) are often strongly related to the lattice structure. Thus, oxides offer tools for structural tuning of spin textures which are not available in metals. In this talk, approaches for creating non-collinear spin textures at coherent interfaces between magnetic oxides will be discussed. These spin textures resemble the spin spirals in some bulk multiferroics (type II) where ferroelectricity is a consequence of the magnetic order. Examples of ferromagnetic La0.7Sr0.3MnO3 films coupled to another 3d, 4d or 5d transition metal oxide at a coherent interface grown by pulsed laser deposition will be addressed. A yet little explored pathway to non-collinear spin textures is to utilize interfaces forming an exchange spring due to strong exchange coupling across the interface. In a moderate magnetic field, such magnetic springs may be twisted on demand. Additionally, interfacial exchange springs can be topologically non-trivial, i. e., neighboring spins are non-coplanar. The design of topological interfacial spin textures which can be switched magnetically as well as electrically may be in reach and promises yet unexplored electronic functionalities.

FD-2:L03  Nanostructured Multiferroic Pb(Zr,Ti)O3-NiFe2O4 Thin-film Composites
A. Matavž, P. Koželj, V. Bobnar, Condensed Matter Physics Dept., Jožef Stefan Institute, Ljubljana, Slovenia; M. Winkler, K. Geirhos, P. Lunkenheimer, Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, Augsburg, Germany

In composites of spinel ferrites and ferroelectric ceramics the magnetoelectric effect arises from direct stress coupling between magnetostrictive (ferromagnetic) and piezoelectric (ferroelectric) grains. We present multiferroic thin-film composites with a novel morphology that provides an extensive connectivity between constituents. They were fabricated by embedding the ferromagnetic NiFe2O4 into self-assembled highly-porous ferroelectric PZT thin films (the latter themselves exhibit extremely interesting functional properties - the porosity-mediated release of the substrate’s mechanical constraints namely boosts their piezoelectric response to the level of bulk ceramics). Detailed structural investigations revealed a two phase pure system, without any chemical reaction between both constituents during synthesis. The multiferroicity is clearly evidenced by detecting both ferroelectric and ferromagnetic hysteresis loops at room temperature. Detected magnetic field-induced changes of the dielectric constant, not only at low frequencies but also above the characteristic frequency of the Maxwell-Wagner behavior, reveal a direct stress coupling between NiFe2O4 and PZT grains and imply a great potential utility of the developed material in magnetocapacitive applications.

FD-2:IL04  Ferroelectric Two-dimensional Electron Gases
J. Bréhin1, F. Trier1, L. M. Vincente-Arche1, P. Hemme2, Y. Chen3, P. Noël7, M. Cosset-Chéneau7, M. D’Antuono3,4, J.P. Attané7, L. Vila7, D. Stornaiuolo3,4, C. Piamonteze5, J. Varignon6, B. Dkhil8, V. Garcia1, S. Fusil1, A. Barthélémy1, M. Cazayous2, M. Salluzzo3, M. Bibes1, 1Unité Mixte de Physique, CNRS, Thales, Université Paris Saclay, Palaiseau, France; 2Laboratoire Matériaux et Phénomènes Quantiques, Université de Paris, France; 3CNR-SPIN, Complesso Monte S. Angelo, Napoli, Italy; 4University of Naples "Federico II", Complesso Monte S. Angelo, Napoli, Italy; 5Swiss Light Source, Paul Scherrer Institut, Villigen PSI, Switzerland; 6CRISMAT, CNRS UMR 6508, ENSICAEN, Normandie Université, Caen Cedex, France; 7Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, Spintec, France; 8Laboratoire Structures, Propriétés et Modélisation des Solides, CentraleSupélec, Université Paris Saclay, CNRS, France

Just as the apparent incompatibility between ferroelectricity and magnetism prompted the renaissance of multiferroics1, the research on « ferroelectric » metals – conjectured in the 1960s by Anderson and Blount2 – was recently revitalized. Yet, their experimental demonstration remains very challenging due to the contra-indication between the presence of free charge carriers and switchable electric dipoles. In this talk we will report on two-dimensional electron gases (2DEGs) formed on Ca-substituted SrTiO3 (STO). Signatures of the ferroelectric phase transition near 30 K are visible in the temperature dependence of the sheet resistance RS and in a strong, reproducible hysteresis of RS with gate voltage3. In addition, spectroscopic explorations of the 2DEG region indicate the presence of switchable ionic displacements. Beyond their fundamental interest in materials physics, ferroelectric 2DEGs offer opportunities in spin-orbitronics: we will show how their spin-charge conversion properties, caused by the inverse Rashba-Edelstein effect, can be electrically tuned in amplitude and sign in a non-volatile way4. These results open the way to a whole new class of ultralow-power spin-orbitronic devices operating without the need for magnetization switching.
1 N.A. Hill, J. Phys. Chem. B 104, 6694 (2000).
2 P.W. Anderson and E.I. Blount, Physical Review Letters 14, 217 (1965).
3 J. Bréhin et al, Phys. Rev. Materials 4, 041002 (2020).
4 P. Noël et al, Nature 580, 483 (2020).

FD-3:IL01  Nanomagnetism of Magnetoelectric Granular Thin-film Antiferromagnets
D. Makarov, Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Ion Beam Physics and Materials Research, Dresden, Germany

Thin film magnetoelectric antiferromagnets (AF) have potential to revolutionize spintronics due to their inherently magnetic-field stable magnetic order and high-frequency operation. To explore their application potential, it is necessary to understand modifications of the magnetic properties of AF thin films with respect to their bulk counterparts. We will outline our developments of zero-offset anomalous Hall magnetometry [1] applied to study the physics of insulating magnetoelectric Cr2O3 antiferromagnets. The analysis of the transport data is backed up by the real space imaging of AF domain patterns using NV microscopy [2,3]. Considering grainy morphology of thin films, we address questions regarding the change of the intergranular exchange [3], criticality behavior and switching of the order parameter [1] and physics of the readout signal in α-Cr2O3 interfaced with Pt [4]. The possibility to read-out the antiferromagnetic order parameter all-electrically enabled a new recording concept of antiferromagnetic magnetoelectric random access memory (AF-MERAM) [2].
[1] T. Kosub et al., Phys. Rev. Lett. 115, 097201 (2015). [2] T. Kosub et al., Nat. Commun. 8, 13985 (2017). [3] P. Appel et al., Nano Lett. 19, 1682 (2019) [4] R. Schlitz et al., Appl. Phys. Lett. 112, 132401 (2018).

FD-3:IL05  Local Writing of Exchange Biased Domains in a Heterostructure of Co/Pd pinned by Magnetoelectric Chromia
U. Singh, presently at XWave; M. Street, presently at Seagate; W. Echtenkamp, C. Binek, S. Adenwalla, University of Nebraska-Lincoln, NE, USA

We demonstrate the writing of micron scaled exchange bias domains by local, laser heating of a thin film hetero-structure consisting of a perpendicular anisotropic ferromagnetic Co/Pd multilayer and a (0001) oriented film of the magnetoelectric antiferromagnet Cr2O3 (chromia). Exchange coupling between chromia’s boundary magnetization and the ferromagnet leads to perpendicular exchange bias. Focused scanning magneto-optical Kerr effect is used to measure local hysteresis loops and create a map of the exchange bias distribution as a function of the local boundary magnetization imprinted in the antiferromagnetic pinning layer on field cooling. The robust boundary magnetization of the Cr2O3 fundamentally alters the exchange bias mechanism, enabling the writing of micron-scaled regions of oppositely directed exchange bias using a focused laser beam.

FD-3:IL07  Magnetoelectric Effect in Composite Ferrite-perovskite Ceramics at Macro- and Microscopic Scales
V.V. Shvartsman1, M. Naveed Ul-Haq2, D. Lewin1, D.C. Lupascu1, 1Institute for Materials Science, University of Duisburg-Essen, Essen, Germany; 2Department of Physics, COMSATS University Islamabad, Chak Shahzad, Islamabad, Pakistan

Multiferroic materials which possess both polar and magnetic orders are considered as potential candidates for the development of magnetic fields sensors, memory elements, electromagnetic energy harvesters, etc. Of particular interest is the coupling between polarization and magnetization, the so called magnetoelectric (ME) effect. Single-phase multiferroics exhibit a noticeable ME effect only at cryogenic temperatures. However, composite multiferroics, which combine separate ferroelectric and magnetic phases, show a strong ME effect at room temperature. We report on the study of the ME effect in bulk multiferroics composites consisting of a ferroelectric based on barium titanate and a ferrimagnetic spinel based on cobalt/ nickel ferrites. The ME effect has been studied both at the macroscopic and nanoscale. The dependences of the magnetoelectric coefficient on the magnetic field, temperature, microstructure of the samples and the relative content of the magnetic phase are discussed. Scanning probe microscopy was used to study the dependence of the local piezoelectric coefficient on the magnetic field. Microscopic measurements made it possible to estimate the change in the ME effect depending on the distance from the interface between the magnetic and ferroelectric phases.

FD-3:IL08  Discovery of Magnetoelectric Quadrupole Order and Visualization of their Domain Structure via Nonreciprocal Linear Dichroism
KENTA Kimura, T. Katsuyoshi, T. Kimura, Department of Advanced Materials Science, The University of Tokyo, Kashiwa, Japan; P. Babkevich, H.M. Ronnow, Laboratory for Quantum Magnetism, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; M. Toyoda, Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan; K. Yamauchi, ISIR-SANKEN, Osaka University, Ibaraki, Japan; Y. Sawada, Center for Advanced High Magnetic Field Science (AHMF), Osaka University, Osaka, Japan; S. Kimura, Institute for Materials Research, Tohoku University, Sendai, Japan

Vortex like spin arrangements called magnetic toroidal, monopole, and quadrupole moments are known as a source for unique symmetry-dependent phenomena such as linear magnetoelectric (ME) effects and nonreciprocal optical responses. However, a guide for the synthesis of materials hosting such ME-active spin arrangements has been limited so far. Here, we successfully discover a ferroic magnetic quadrupole order in a new material Pb(TiO)Cu4(PO4)4, which consists of magnetic Cu4O12 square cupola units [1,2]. Besides conventional linear ME effects, we observe a peculiar optical response for visible light called nonreciprocal linear dichroism, i.e., the sign of the linear dichroism is reversed between two counter-propagating light beams. Furthermore, using this optical effect, we successfully visualize spatial distributions of quadrupole domains and their isothermal electric-field switching by means of a transmission-type polarized light microscope [3]. If time allows, we will also present our recent discovery of an antiferromagnet exhibiting large nonreciprocal directional dichroism due to a magnetic toroidal moment.
[1] K. Kimura et al., Nat. Commun. 7, 13039 (2016). [2] K. Kimura et al., Phys. Rev. B 97, 134418 (2018). [3] K. Kimura et al., Commun. Mater. 1, 39 (2020).

FD-3:L09  Organic Multiferroics
Shenqiang ren, University at Buffalo, The State University of New York, Buffalo, NY, USA

Molecular ferroics are considered as an alternative to inorganic ferroics due to their structural diversity, optical chirality and flexibility, as well as low-temperature solution processing. A significant amount of molecular ferroics (ferroelectrics and magnets) have been developed and studied for their fundamental mechanisms and potential applications in electronic devices. A challenging task in this area is to design molecular materials and assemble them into desired structural forms, so that their unique ferroic properties can be harvested at high temperature. In this talk, I will discuss my group’s recent research on the materials design and self-assembly of high temperature molecular ferroelectrics, magnets and multiferroics, and promising prospects in molecular ferroic devices.

FD-3:IL10  Controlling the Electrical, Magnetoelectric and Thermal Properties in Epitaxial-strain-engineered Ferroic Films
E. LANGENBERG, Department of Condensed Matter Physics, Universitat de Barcelona, Barcelona, Spain

Ferroic materials provides an excellent playground to explore the interactions between different properties such as magnetic and electric or electric and thermal. The former interaction is the main driving force in the interest in materials possessing ferroelectric and magnetic order. The latter has recently opened a new avenue for the electric-control of the phonon transport. In this talk the two interactions are to be discussed based on epitaxial multiferroic Sr1-xBaxMnO3 films and epitaxial ferroelectric PbTiO3 films.
The perovskite (Sr,Ba)MnO3 system is an ideal candidate for tailoring electrical and magnetoelectric properties through the accurate control of Ba content and epitaxial strain due to the strong coupling between polar instability, spin order, and lattice. I will demonstrate here the interplay between dielectric and magnetic properties, which can lead to 50% drop in the dielectric constant with the emergence of the magnetic order.
Regarding the prototype ferroelectric PbTiO3, strain-engineering is used to design different domain patterns. I will show that the thermal conductivity is strongly affected by the type and density of domain walls, achieving a 61% reduction compared to the single-domain scenario.

FD-3:IL11  Multiferroics: Recent Developments and Trends
A. Loidl, Center for Electronic Correlations and Magnetism, University of Augsburg, Augsburg, Germany

In this talk I will review recent developments in the field of spin-driven multiferroicity, namely i) magnetic skyrmions dressed with ferroelectric (FE) polarization, ii) multiferroic spin supersolid and superliquid phases and finally iii) ferroelectricity induced by vector chirality. The lacunar spinels GaV4X8 (X = S, Se) undergo orbital ordering close to 40 K accompanied by FE order and reveal complex magnetic phase diagrams at low temperatures, including ferromagnetic, cycloidal and Néel-type skyrmion-lattice phases. Skyrmions are topologically protected nanoscale spin vortices and in lacunar spinels it has been shown that this nanoscale whirl-like structures carry sizable FE polarization. The spinel compound MnCr2S4 reveals a Yafet-Kittel-type antiferromagnetic triangular structure at low temperatures. In external magnetic fields up to 100 T this compound reveals a number of complex spin pattern, including an ultra-robust magnetization plateau in addition to multiferroic supersolid and superliquid phases. Finally, I document that in LiCuVO4 in the paramagnetic phase the existence of long-range ordered vector chirality appears as precursor of the low-temperature multiferroic spin-spiral phase and induces long-range FE order in the absence of conventional long-range spin order.

FD-4:IL03  Optical Magnetoelectric Effect in Multiferroics
YOUTAROU TAKAHASHI, Department of Applied Physics and Quantum Phase Electronics Center (QPEC), University of Tokyo, Tokyo, Japan; RIKEN Center for Emergent Matter Science (CEMS), Saitama, Japan

Symmetry breaking of matter is responsible for the optical effect. The multiferroics, which exhibit the magnetically-induced ferroelectricity, break the time-reversal and space-inversion symmetries, leading to the optical magnetoelectric (OME) effect characterized by the nonreciprocity. The electromagnon, which is electrically active spin excitation inherent to the multiferroics, shows the strong dynamical ME coupling, resulting in the resonantly enhanced OME effects including the nonreciprocal directional dichroism and the gyrotropic birefringence. Here we demonstrate the OME effect on the electromagnon in several helimagnets by using the time-domain terahertz spectroscopy. The directional dichroism, which cause the optical diode effect, is found to be enhanced by the inter-mode coupling between the electromagnons. On the other hand, the gyrotropic birefringence can be observed as the nonreciprocal rotation of light polarization, which is distinguished from the Faraday effect and from the natural optical activity. We reveal the nature of gyrotropic birefringence by using the terahertz polarimetry by comparison with other polarization rotation phenomena. These results clearly demonstrate that the novel optical functionality of OME effect.

FD-4:L05  High-frequency Molecular Dynamics Simulations of the Electrocaloric Effect in Ferroelectric PbTiO3
S. Lisenkov, University of South Florida, Tampa, FL, USA

The electrocaloric effect (ECE) is associated with a reversible change in temperature under adiabatic application of an electric field or with a reversible change in entropy under isothermal application of the electric field. In this work we (i) propose a computational approach capable of harvesting isothermal heat and entropy change in Molecular Dynamics simulations; (ii) tailor this approach to simulations of all essential electrocaloric metrics along with their time evolution; and (iii) apply the methodology to reveal the basic dynamical features of the ECE in ferroelectric PbTiO3. Application of the methodology to study high-frequency dynamics in ferroelectric PbTiO3 revealed that the ECE persists up to the frequencies associated with the onset of dielectric losses which result in the irreversible heat creation. As these frequencies depend strongly on the temperature the intrinsic limit for the ECE is also temperature dependent. We found no differences between the electrocaloric metrics from the simulations under the ac and square-wave electric field, which suggests that the ECE is independent of the electric field profile or its rate of application.

FD-4:L06  Microstructure and Electro-optic Response of Thick Epitaxial BaTiO3 Films Integrated on Silicon (001) for Applications in Silicon Photonics
M. Reynaud1, W. Li1, A.B. Posadas1, A.A. Demkov1, Z. Dong2, D. Wasserman2, H. Park3, 4, J.H. Warner3, 4, W. Cao5, G.Z. Mashanovich5,
1Department of Physics, University of Texas at Austin; 2Department of Electrical and Computer Engineering, University of Texas at Austin; 3Materials Science and Engineering Program and Texas Materials Institute, The University of Texas at Austin, Austin, TX, USA; 4Walker Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA; 5Optoelectronics Research Centre, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton, UK

Advances in epitaxial oxide deposition enabled fabrication of ferroelectric BaTiO3 films capable of providing a robust electro-optic (EO) response [1]. This created a plethora of potential applications in silicon photonics ranging from optical interconnect to optical neuromorphic and quantum computing [2]. We report a microstructure analysis and deposition process of thick EO-active BaTiO3 films integrated on Si(001). Geometric phase analysis (GPA) was performed to explore the film microstructure. Phase field simulations were used to interpret the GPA. The electro-optic properties of the films have been measured in free space as well as using Si waveguides, deposited atop the film, and correlate well with the microstructural analysis and demonstrate the potential of Si-integrated BaTiO3 for silicon photonics [3].
[1] W. Guo, et al., “The Epitaxial Integration of BaTiO3 on Si for Electro-Optic Applications,” J. of Vac. Sci. Technol. A 39, 030804 (2021). [2] A. A. Demkov et al., “Materials for emergent silicon-integrated optical computing,” J. Appl. Phys. 130, 070907 (2021). [3] A. B. Posadas, et al., “Thick BaTiO3 epitaxial films integrated on Si by RF sputtering for electro-optic modulators in Si photonics," ACS App. Mat. & Interf., https://doi.org/10.1021/acsami.1c14048

FD-4:IL10  Taylored Magnetostrictive Multilayers for Magnetoelectric Sensors
D. Meyners, Inorganic Functional Materials, Institute of Materials Science, Faculty of Engineering, Kiel University, Kiel, Germany

Taylored magnetostrictive multilayers are very interesting composite materials for highly sensitive magnetoelectric (ME) magnetic-field sensors with low detection limits in the range of 100 pT/rt(Hz) and below [1]. To further improve the detection limit, a high degree of control over the magnetization state of the magnetostrictive phase is required. The presentation considers ME sensors based on magnetostrictive multilayers of the sequence Ta/Cu/MnIr/FeCoSiB. Here, the amorphous, magnetostrictive FeCoSiB layers are prepared by either RF or DC sputter deposition. The resultant magnetic properties of the different magnetic materials are compared to each other and correlated with the ME sensor properties such as noise level and detection limit. A significant magnetic noise suppression is observed when the multilayers are designed according to an antiparallel exchange biasing scheme [2].
(1) S. Salzer, et al., "Noise Limits in Thin-Film Magnetoelectric Sensors With Magnetic Frequency Conversion," in IEEE Sensors Journal, vol. 18, no. 2, pp. 596-604, 2018. (2) Jovičević Klug, M.; Thormählen, L.; Röbisch, V.; Toxværd, S. D.; Höft, M.; Knöchel, R.; Quandt, E.; Meyners, D.; McCord, J.: Applied Physics Letters 114 (2019), 192410. Funding by the DFG CRC 1261 is gratefully acknowledged.


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