Multifunctional oxides represent a broad family of compounds with properties ranging from topological, (multi) ferroic, superconducting, electronically correlated etc… promising a wealth of genuine properties applicable to a large variety of technologically relevant topics. LNO is particularly interested in several of them, with materials either in thin film form (thanks to our oxide deposition systems, namely atomic oxigen assisted molecular beam epitaxy, OA-MBE, and pulsed laser deposition, PLD) or single crystalline (flux growth for instance).
Energy applications
The production of hydrogen by solar water splitting is a very promising technique. In recent decades, oxide materials have attracted much attention for use as photoanodes. Unfortunately, pure oxide photoanodes exhibit low performance because of a number of limiting processes including: high recombination rates, unfavorable large band gaps, position of conduction band too low with respect to the water redox levels, or low kinetic reaction at the photoanode /aqueous interface. In LNO we elaborate oxide photoanodes by AO-MBE and by aqueous chemical growth (ACG). Subsequently, we characterize their photoelectrochemical properties and try to understand and describe the mechanisms underlying the OER (oxygen evolution reaction) at the microscopic scale, taking advantage of complementary advanced experiments using synchrotron radiation and collaboration with theoreticians. For example, for hematite based photoanodes we studied: the role of surface states[1], the influence of annealing temperature and gas atmosphere[2] (figure 1) and the role of Ti doping in the improvement of the photocurrent and decrease of the amount of water absorbed on the surface[3]. For single crystalline TiO2 layers, we studied the role of the crystallographic structure[4] and in epitaxial BaTiO3 the influence of electrical polarization[5] and nitrogen doping[6].
[1] Characterizing surface states in hematite nanorod photoanodes, both beneficial and detrimental to solar water splitting efficiency, Dana Stanescu, Mekan Piriyev, Victoria Villard, Cristian Mocuta, Adrien Besson, Dris Ihiawakrim, Ovidiu Ersen, Jocelyne Leroy, Sorin G. Chiuzbaian, Adam P. Hitchcock, Stefan Stanescu, J. Mater. Chem. A, 2020, 8, 20513-20530, DOI: 10.1039/D0TA06524B
[2] Enhancement of the Solar Water Splitting Efficiency Mediated by Surface Segregation in Ti-doped Hematite Nanorods, Stanescu S, Alun T, Dappe YJ, Ihiawakrim D, Ersen O, Stanescu D., ACS Appl. Mater. Interfaces 2023, 15, 22, 26593–26605, DOI: 10.1021/acsami.3c02131, Open access DOI: 10.26434/chemrxiv-2023-sxnbn-v2
[3] Unraveling the Surface Reactivity of Pristine and Ti-Doped Hematite with Water, Pierre-Marie Deleuze, Héléne Magnan, Antoine Barbier, Mathieu Silly, Bruno Domenichini, and Céline Dupont, The Journal of Physical Chemistry Letters 2021, 12, 47, 11520-11527, DOI: 10.1021/acs.jpclett.1c03029
[4] Epitaxial TiO2 thin film photoanodes : influence of crystallographic structure and substrate nature, H. Magnan, D. Stanescu, M. Rioult, E. Fonda A. Barbier, J Phys Chem C 123, 5240 (2019), DOI: 10.1021/acs.jpcc.8b11479
[5] Tuning the Charge Carriers Migration in Epitaxial BaTiO3 Thin-Film Photoanodes, H. Magnan, P. M. Deleuze, J. Brehin, T. Plays, D. Stanescu, W. R. Flavell, M. G. Silly, B. Domenichini, and A. Barbier, J. Phys. Chem C 124, 10315 (2020), DOI: 10.1021/acs.jpcc.0c01361
[6] Properties of self-oxidized single crystalline perovskite N: BaTiO3 oxynitride epitaxial thin films, Anyssa Derj, Helene Magnan, Cristian Mocuta, Patrick Le Fevre, Jocelyne Leroy and Antoine Barbier, Mater. Adv., 2022, 3, 3135, DOI: 10.1039/d1ma01082d
[7] P. Vasconcelos Borges Pinho, A. Chartier, D. Menut, A. Barbier, M. O.J.Y. Hunault, Ph. Ohresser, C. Marcelot, B. Warot-Fonrose, F. Miserque, J.-B. Moussy, “Stoichiometry Driven Tuning of Physical Properties in Spinel Oxide Layers”, Applied Surface Science 615, 156354 (2023).
Figure 1: (left) evolution of the photocurrent for different hematite based photoanodes grown by ACG; (right) the photocurrent as a function of the applied potential for a representative sample.
Perspectives: Thanks to several ANR projects (OPTYMAL (2020-2024) and OERKOP (2023-2027)), we could develop both in situ and operando experiments in order to study at the microscale the OER (oxygen evolution reaction) at the interface between the photoanode and the electrolyte. These new setups open new opportunities for photoanodes characterization and optimization such as the role of surface catalyzers on the OER mechanism (as a function of applied potential), and the stability (reversible and irreversible phenomena) of the electrode during the electrochemical process. Moreover, the gas analyzer recently purchased at LNO, will allow us to measure the H2 produced during the solar water splitting reaction and therefore we will be able to estimate the Faraday efficiency for each photoanode. We will also continue to test new photoanode compositions, as e.g. oxynitrides with perovskite structure, which are promising for solar water splitting applications. Our originality relies on a strong ongoing collaboration with the SOLEIL synchrotron allowing for a fine characterization of our samples and complementary DFT calculations. Collaborations with researchers from SOLEIL synchrotron, IPCMS, ICMMO and ICB Bourgogne will continue, and will expand by integrating for instance the chemistry network (“Réseau Métier : Chimie”) initiated by DRF at CEA.Concerning our corrosion activity, we will explore the physicochemical and structural properties of (Mn,Co)3O4 in order to contribute to the elaboration of Mn-Co-O phase diagrams and electronic transport models based on the relationship between order/disorder, magnetic properties and resistivity of (Mn,Co)3O4. This is justified by the promises this system holds as protective conductive layers on ferritic stainless steel used in solid oxide fuel cells for green hydrogen production.
Multiferroics
[coll. Lab. Albert Fert, Lab. Charles Coulomb, Synchrotron SOLEIL]
Building on the momentum of the previous reporting period, we have continued our efforts to explore the rich physics of intrinsic and artificial multiferroic textures. The archetypical representative of the former is the magneto-electric antiferromagnet BiFeO3 (BFO). It exhibits a natural chiral order, which is particularly attractive for potentially hosting topological ferroic entities such as skyrmions. This is the focus of two projects: the FET Open TSAR andthe ANR project TATOO. Resonant elastic X-ray scattering (in which we invested a substantial effort) and nitrogen vacancy magnetometry imaging were used to reveal and understand the complex electrical and antiferromagnetic textures in BFO bulk crystals and strained films. We could thus reveal interesting topological textures at the domain walls of ferroelectrically striped BFO[1],[2],[3], the presence of antiferromagnetic topological defects at the surface of bulk BFO[4] and the onset and control of single antiferromagnetic cycloidal state in thin layers[5].
Searching for a way of generating antiferromagnetic skyrmions, we have invested some effort on atomistic simulations (PhD of Zixin Li) with the result of pinpointing the ideal conditions in strain-engineered BFO thin layers[6]. Another substantial work has been invested in the upgrade of the second harmonic optical setup with ultrafast time-resolution capabilities, which we use to explore the ultrafast dynamics of multiferroic textures in thin epitaxial layers. Finally, a scattering near-field optical microscope is currently developed to address the physics of ferroic textures at the nanoscale.
[1] Chauleau, J.-Y. et al. Electric and antiferromagnetic chiral textures at multiferroic domain walls. Nat. Mater. 19, 386–390 (2020).
[2] Fusil, S. et al. Polar Chirality in BiFeO3 Emerging from A Peculiar Domain Wall Sequence. Adv. Electron. Mater. 8, 2101155 (2022).
[3] Haykal, A. et al. Antiferromagnetic textures in BiFeO3 controlled by strain and electric field. Nat. Commun. 11, 1704 (2020).
[4] Finco, A. et al. Imaging Topological Defects in a Noncollinear Antiferromagnet. Phys. Rev. Lett. 128, 187201 (2022).
[5] Dufour, P. et al. Onset of Multiferroicity in Prototypical Single-Spin Cycloid BiFeO3 Thin Films. Nano Lett. 23, 9073–9079 (2023).
[6] Li, Z. et al. Multiferroic skyrmions in BiFeO3, Phys. Rev. Res. 5, 043109 (2023).
Figure 2: a) Schematic representation of resonant elastic X-ray scattering probing a BFO multiferroic texture. (from Chauleau et al.), b) Simulated stable antiferromagnetic skyrmions in a BFO thin layer (from Li et al.).
Beside intrinsic compounds, artificial multiferroic heterostructures have also been synthesized by PLD and O-MBE, including ferrite spinel (e.g.: CoFe2O4, NiFe2O4, FeCr2O4) and perovskite (e.g.: BaTiO3, La2/3Sr1/3MnO3) structures. Their characterization relies on laboratory methods as well as detailed synchrotron radiation studies[1] that have evidenced cross correlated properties[2] in MFe2O4/BaTiO3 bilayers (M= Co, Ni, Mn) as well as chemical reduction experienced by the ferrite layer under application of a local electrical polarization.n depth studies of the ferroelectric properties of BaTiO3 layers were also performed and complemented by DFT calculations[3].
[1] C. Mocuta, P. Ohresser, A. Barbier, « Chap.18 – Artificial laminar oxide multiferroic magnetoelectric thin film structures: Elaboration methods and study by synchrotron radiation techniques », Book chapter in Perovskites and other Framework Structure Crystalline Materials p.511, Coll. Acad. (2021). Open Access Journal Materials and Devices ISBN: 2495-3911, DOI 10.23647/ca.md20202604.
[2] Cross-Correlation between Strain, Ferroelectricity, and Ferromagnetism in Epitaxial Multiferroic CoFe2O4/BaTiO3 Heterostructures, N. Jedrecy, T. Aghavnian, J-B. Moussy, H. Magnan, D. Stanescu, X. Portier, M-A. Arrio, C. Mocuta, A. Vlad, R. Belkhou, P. Ohresser, A. Barbier, ACS Appl. Mater. Interfaces, 2018, 10 (33), pp 28003–28014, DOI: 10.1021/acsami.8b09499
[3] Nature of the Ba 4d Splitting in BaTiO3 Unraveled by a Combined Experimental and Theoretical Study, Pierre-Marie Deleuze, Helene Magnan, Antoine Barbier, Li Zheshen, Alberto Verdini, Luca Floreano, Bruno Domenichini, and Céline Dupont, J. Phys. Chem. C 2022, 126, 15899. DOI: 10.1021/acs.jpcc.2c02510
Figure 3 : a) High transmission electron microscopy (HRTEM) cross section of a NiFe2O4/BaTiO3 bilayer (coll. CEMES-CNRS). b) Reciprocal space map of a fully relaxed CoFe2O4/BaTiO3 (CFO/BTO)bilayer. c) Piezo-force microscopy (PFM) measurement on a CFO/BTO bilayer. d) VSM hysteresis loops vs temperature for a NiFe2O4 (16nm)/BaTiO3 (5.6nm) bilayer.
Perspectives: Many open issues of the physics underlying exotic ferroic textures and their dynamics in nanolayers have still to be tackled. We believe that not only fascinating fundamental questions remain to be understood but mastering these textures could be an important asset for future information technologies. Consequently, based on the solid work already achieved, we will continue our effort in addressing these issues. In particular, multiferroïc interfaces are of central interest to control the interaction between different orders. The interface reduction effects observed on these interfaces during polarisation are currently exploited in an ongoing project to realize nanocircuits. To better Taylor the interactions, nanostructuration and additional anion doping will be explored. In particular, we will consider O substitution by N to realize oxynitrides that promise new properties, knowing that the essential tools have already been developed.
On another front, we will tackle the experimental exploration of antiferromagnetic skyrmions in BiFeO3 thin epitaxial layers. That would represent a significant achievement, considering the yet-to-be-demonstrated stabilization of real AF skyrmions. Several leads will be followed including strain engineered multiferroic textures, or nucleation induced by light carrying orbital angular moment or ultrafast spin-transfer torque. Once successful, new horizons for the physics of antiferromagnetic topological entities will unfold. On the other hand, a new class of ferroic textures exhibiting antipolar alignments are currently emerging, namely the antiferroelectrics. We plan to use our expertise in second harmonic generation (SHG) imaging to understand the antiferroelectric/ferroelectric phase transitions. In a broader sense, time-resolved SHG will be a focal point of our activity for the next years, with the specific objective of exploring a broader range of excitations (e.g. THz, MIR, NIR, UV). We believe that mastering the dynamics of exotic ferroic textures in the THz range would pave the way to the emergence of a next generation of frugal THz technonogies. Finally, a substantial effort will be focused on addressing these issues at the nanoscale with the establishment of an activity on near-field optical imaging.
Quantum materials
The physics of strongly correlated systems is extremely rich and complex. Scientific breakthroughs require excellent quality samples with controlled doping. In LNO, we synthesize pure or substituted materials in the form of single crystals and thin films that we study in collaboration with several national and international laboratories. In this field our areas of research are the exploration of the phase diagram of high Tc superconductors, the study of new Mott insulators and Weyl semi-metals.
- Superconductors (coll. LNCMI Toulouse, Univ. Sherbrouke, MPQ Paris, LPS):
Since the discovery of superconducting copper oxides in 1986, a new physics has emerged, that of the interacting orders of matter where magnetism and superconductivity intertwine. This field is full of new surprises with the discovery of several symmetry breakings (translation, rotation in space, time reversal) observed in the same phase called the pseudogap phase. It is in this context that we synthesize high-quality mercury cuprates in the framework of several ongoing collaborations. In particular, high field measurements in Toulouse (coll. LNCMI) of quantum oscillations and Hall effect have evidenced the coexistence of antiferromagnetic and charge orders in the under-doped material[1]. Moreover, we could demonstrate the similar energy scales between charge density waves and superconductivity gap[2]and the T-linear resistivity at low-temperature in the 2-CuO2 layer compound Bi2Sr2CaCu2O8+d, reminiscent of the proximity of a quantum critical point, and associated with a universal scattering rate[3].
[1] Magnetotransport signatures of antiferromagnetism coexisting with charge order in the trilayer cuprate HgBa2Ca2Cu3O8+δ, Oliviero, V; Benhabib, S; Gilmutdinov, I; Vignolle, B; Drigo, L; Massoudzadegan, M; Leroux, M; Rikken, GLJA; Forget, A; Colson, D; Vignolles, D ; Proust, C; Nature Comm. 13, 1568 (2022).
[2] B. Loret, Y. Gallais, M. Cazayous, A. Forget, D. Colson, M.-H. Julien, I. Paul, M. Civelli, A. Sacuto. Intimate link between Charge Density Wave, Pseudogap and Superconducting Energy Scales in Cuprates, Nature Physics, 15, 771, 2019, doi.org/10.1038/s41567-019-0509-5.
[3] A.Legros, S. Benhabib, W. Tabis, F. Laliberté, M. Dion, M. Lizaire, B. Vignolle, D. Vignolles, H. Raffy, Z. Z. Li, P. Auban-Senzier, N. Doiron-Leyraud, P. Fournier, D. Colson, L. Taillefer, C. Proust. Universal T-linear resistivity and Planckian limit in overdoped cuprates, Nature Physics, 15, 142, 2019, doi.org/10.1038/s41567-018-0334-2
Figure 4: High-Tc superconducting phase and image of a crystal sithesized in the laboratory. These were used to establish the phase diagram (right).
We also synthesized and characterized single crystals of the one-dimensional iron-based compound, BaFe2Se3, multiferroic type II near room temperature (~200K) and superconductor under high pressures. Studies by powder neutron diffraction and Fe Kβ X-ray emission spectroscopy under high pressure (coll. LPS) were carried out at ILL and at SOLEIL at the boundary between the magnetic and superconducting phases. The measurements show that the magnetic ground state is destabilized under pressure (above 3-4 GPa) giving rise to a new stripe-shaped antiferromagnetic spin order, similar to the magnetic order of the parent superconductor BaFe2S3 [1]. This discovery shows that the striped phase in the vicinity of the superconducting dome is of central importance as its particular magnetic fluctuations could be involved in the stabilization of superconductivity.
[1] W.G. Zheng, V. Balédent, P. Foury-Leylekian, V. Colin, F. Damay, J.-P. Rueff, A. Forget and D. Colson, Universal stripe order in the vicinity of the superconducting phase in pressurized BaFe2Se3 Spin Ladder, Communications Physics 5, 183 (2022).
- Topological systems (Coll. LPS, SOLEIL):
Iridate phases have been highly investigated because of their strong spin-orbit coupling combined with electronic correlations leading to unconventional physical properties. Here, the “Ruddlesden-Popper” perovskite family presents three compounds with exciting properties: (i) Sr2IrO4, the most strongly correlated compound, antiferromagnetic at low temperature, is the archetype of the “Mott-spin-orbit insulator”, (ii) Sr3Ir2O7, is also an antiferromagnetic insulator but with weaker electronic correlations and (iii) the semi-metal SrIrO3, has a three-dimensional crystallographic structure and presents a nodal line protected by symmetry following band calculations.
Figure 5: Dispersions images obtained by ARPES on Sr2IrO4, Sr3Ir2O7 single crystals and a SrIrO3 thin film from the PhD. thesis of P. Foulquier (2022).
Therefore, we have analyzed these three compounds by synthesizing pure and substituted single crystals and thin films[1]. All samples have been characterized and measured by Angle Resolved Photoemission Spectroscopy (ARPES). The influence of epitaxial strain and growth direction of SrIrO3 thin films on the electronic structure were studied and in particular the impact of symmetry breakings on Dirac points morphology[2]. We used ruthenium substituted Sr2IrO4 and Sr3Ir2O7 single crystals to investigate the transition from an antiferromagnetic insulator to a non-magnetic metal[3]. We also explored the evolution of the electronic structure of single crystals through the Néel transition tuned by ruthenium or lanthanum substitutions. These experimental results were confronted to theoretical models, in particular in the framework of Dynamical Mean Field Theory (DMFT).
[1] L. Fruchter, V. Brouet, D. Colson, J.-B. Moussy, A. Forget, Z. Z. Li, “Electrochemical oxygen intercalation into Sr2IrO4”,Journal of Physics and Chemistry of Solids 112, 1 (2018).
[2] V. Brouet, P. Foulquier, A. Louat, F. Bertran, P. Le Fèvre, J. Rault, D. Colson, “Origin of the different electronic structure of Rh- and Ru-doped Sr2IrO4”, Phys. Rev B. 104, L121104 (2021).
[3] P. Foulquier, M. Civelli, M. Rozenberg, A. Camjayi, J. Bobadilla, D. Colson, A. Forget, P. Thuery, F. Bertran, P. Le Fevre, V. Brouet, “Evolution of the spectral lineshape at the magnetic transition in Sr2IrO4 and Sr3Ir2O7”, Eur. Phys. J. B. 96:42 (2023).
Perspectives: Some systems in single crystal form are much in demand and have been in the forefront of international research for many years. This is the case of high-Tc superconductors (like HgBa2Ca2Cu3O8+δ and Bi2Sr2CaCu2O8+d) where our expertise in synthesizing high-quality single crystals has allowed us to be an important brick of relevant and timely studies for many years. We intend to continue in this vein while developing further on the project lead by J.-F. Roch (ENS Paris-Saclay) aiming at studying quantum materials at pressures above 100 GPa in a diamond anvil cell. These pressures lead to record critical temperature superconductivity in copper oxide crystals (cuprates) and hydrogen-rich molecular compounds (hydrides). The idea here is to engineer nitrogen-vacancy (NV) centers in diamond anvils and use these in situ sensors to optically detect the Meissner effect as the indisputable proof of superconductivity. Single crystals of HgBa2Ca2Cu3O8+δ are the ideal samples for such measurements.
Moreover, the activity around the multiferroic/superconductor BaFe2Se3 compound will evolve, partly with the addition of SHG studies here in LNO. Finally, the synthesis and characterization of single crystals of the magnetic and correlated compound Co3Sn2S2 with the Kagomé structure will be developed. This compound is very interesting as it is a magnetic Weyl semi-metal with a record anomalous Hall effect. We will study in detail the filling of its bands, the strength of spin-orbit coupling and magnetic interactions in collaboration with the LPS. On the other hand, we do not plan to continue working on iridates. However, a very important condition for the single crystal activity to continue is the resolution of some internal (health-related) issues as well as the replacement of the glass blower outside SPEC (but in CEA).