The Oxitronics team is part of the CNRS/Thales laboratory located within Thales Research and Technology in Palaiseau, France. Our main scientific interests are in oxide electronics, spintronics, multiferroics, ferroelectrics and oxide interfaces. This website contains information on our past and current research, our group members and our publications. See also our events page for information on workshops, schools, etc.
Along with Dutch chemist Daniël Vanmaekelbergh our group member Manuel Bibes will receive the Descartes-Huygens Prize 2017. That was announced today by the Royal Netherlands Academy of Arts and Sciences (KNAW), the Embassy of France in the Netherlands and the Académie des Sciences. The two nanoscientists have been awarded the prize for their outstanding research and their contribution to Franco-Dutch relations. Manuel will use his Descartes-Huygens Prize to spend three months conducting research at the Center for Cognitive Systems and Materials at the University Groningen. He will also visit the nanolaboratories at the University of Twente. The three organisations aim to combine their expertise to develop low-power electronics.
As the old adage goes, Seeing is believing! This is particularly acute for antiferromagnets that despite their interest for low-power, ultrafast spintronics applications remain practically impossible to image at the nanoscale since their the antiparallel order of neighbouring spins results in a vanishing magnetization. Usually, reciprocal-space, bulk averaging methods such as neutron diffraction are the techniques of choice to characterize antiferromagnets, but then microscopic details remain concealed. In our recent paper just published in Nature, we report the first real-space imaging of long-range periodic order in a complex antiferromagnet, bismuth ferrite (BiFeO3). We have used a new technique exploiting the extreme magnetic sensitivity of the photoluminescence response of a single nitrogen-vacancy (NV) center located near the apex of an atomic force microscope tip. In addition, we have also taken advantage of the magnetoelectric coupling present in BiFeO3 to evidence the electrical control of the cycloid propagation direction in real space. Besides highlighting the potential of NV magnetometry for imaging complex antiferromagnetic orders at the nanoscale, our results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures on-demand.
This work was performed in collaboration with Lab. Charles Coulomb, CEA-Saclay, C2N, Synchrotron SOLEIL, Lab. Aimé Cotton and University of Basel. Left image on figure courtesy of P. Maletinsky.
Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer
I. Gross et al ; Nature 459, 252 (2017)
Our group member Agnès Barthélémy has just been awarded the Lazare-Carnot Prize of the French Academy of Science. This Prize created by the French Ministry of Defence acknowledges important advances in fundamental research with perspectives of civilian or military applications. Congratulations Agnès !
On July 13, 2017, Vincent Garcia defended his Habilitation Thesis in Palaiseau. He presented his ~10 year work on ferroelectric tunnel junctions, from their physical principle of operation through their combination with spintronics to their use as memristors. He also gave perspectives and proposed future directions of research. Lots of exciting new concepts to explore. Well done, Vincent !
The quasi two- dimensional electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge; another is the extreme sensitivity of its transport properties to electrostatic boundary conditions. This surface-interface coupling was previously exploited to modulate both carrier densities and mobilities of the q2DES through the controlled adsorption of polar solvents and by capping with different materials. In our recent work just published in Advanced Materials, we investigate in detail the chemical, electronic and transport properties of several LAO(1-2 uc)/STO samples capped with different metals (Ti, Ta, Co, Ni80Fe20 – NiFe -, Nb, Pt, Pd and Au) grown in a ultra-high vacuum (UHV) system combining pulsed laser deposition (to grow the LAO), sputtering (to grow the metal) and in situ X-ray photoemission spectroscopy (XPS). The results confirm that for several metals a q2DES forms at 1-2 uc of LAO. Additionally, XPS shows that the appearance of interfacial conductivity is accompanied by a partial oxidation of the metal, a phenomenon that is strongly linked with the q2DES properties and with the formation of defects in this system. In contrast, for noble metals, the q2DES does not form at low LAO thicknesses and instead the critical thickness is increased above 4 unit cells. We discuss the results in terms of a hybrid mechanism that incorporates both electrostatic and chemical effects.
Tuning up or down the critical thickness in LaAlO3/SrTiO3 through in situ deposition of metal overlayers
D.C. Vaz et al ; Adv. Mater. 10.1002/adma.201700486 (2017)
More than 80% of known magnetic substances have dominant antiferromagnetic interactions. As it generates no stray field, the antiferromagnetic order is very discreet, which makes the processes of nucleation or growth of domains, as well as their responses to external stimuli at the microscopic scale, a virtually uncharted territory. The scarcity of real‑space imaging techniques devoted to this class of magnetic materials is a major bottleneck to understanding the fundamental basis of their manipulation.
In this paper just published in Nature Materials, we use second harmonic generation with unprecedented sub-micron resolution to image antiferromagnetic order in BiFeO3 thin films. We provide a direct visualization of the antiferromagnetic domains in a single ferroelectric one. these antiferromagnetic domains can be manipulated thanks to magnetoelectric coupling in this archetypal multiferroic. More unexpectedly, we are also able to manipulate the antiferromagnetic domains independently of the ferroelectric polarization, using electric fields significantly lower than the ferroelectric coercivity or using optical stimuli such as THz pulses generated by a femtosecond laser. This opens horizons to manipulate the antiferromagnetic order in multiferroics and brings new insights into the emerging field of antiferromagnetic spintronics.
This work was performed in collaboration with CEA-Saclay.
Multi-stimuli manipulation of antiferromagnetic domains assessed by second-harmonic imaging
J.-Y. Chauleau et al ; Nature Mater. 10.1038/nmat4899 (2017)
Rare-earth nickelates are intringuing perovskite oxides showing metal-insulator transition tuneable by the rare-earth size, and complex antiferromagnetic order at low temperature. Yet, a complete theoretical description of their rich phase diagram was missing. In this work just out in NPJ Quantum Materials, we have used first-principles simulations to describe their electronic and magnetic experimental ground state. We show that the insulating phase is characterized by a split of the electronic states of the two Ni sites (i.e. resembling low-spin 4+ and high-spin 2+) with a concomitant shift of the oxygen-2p orbitals toward the depleted Ni cations. Therefore, from the point of view of the charge, the two Ni sites appear nearly identical whereas they re in fact distinct. Performing such calculations for several nickelates, we have built a theoretical phase diagram that reproduces all their key features, namely a systematic dependence of the MIT with the rare-earth size and the crossover between a second to first order transition for R=Pr and Nd. Our results hint at strategies to control the electronic and magnetic phases of perovskite oxides by fine tuning of the level of covalence.
This work was performed thanks to collaboration with LIST.
Complete phase diagram of rare-earth nickelates from first-principles
J. Varignon et al ; NPJ Quant. Mater. 2, 21 (2017)