Welcome to our website !

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.

Learning with solid-state ferroelectric synapses

CP_IA-Biomem_CNRS_image.pngArtificial neural networks show enhanced performance for key applications such as data mining or pattern recognition, but need to be implemented in hardware to make these applications accessible to everyone. Memristors are the electronic equivalent of synapses, whose variable connecting strength is at the heart of the learning process.

Accurate modelling of memristor dynamics is essential for the development of autonomous learning in artificial neural networks. In this paper, we demonstrate that spike-timing-dependent plasticity can be harnessed from inhomogeneous polarization switching in ferroelectric memristors. Combining time-dependent transport measurements, ferroelectric domain imaging, and effective-Hamiltonian-based atomistic molecular dynamics simulations, we show that the ferroelectric switching underlying resistance changes in these devices can be described by a nucleation-limited model. Using this physical model, we can reliably predict the conductance evolution of ferroelectric synapses with varying neural inputs. These results pave the way toward low-power hardware implementations of billions of reliable and predictable artificial synapses in future brain-inspired computers.

This work was performed thanks to collaboration between CNRS-Thales, Univ. of Bordeaux, Univ. of Arkansas, Centre de Nanosciences et de Nanotechnologies, and Thales Research and Technology.

Learning through ferroelectric domain dynamics in solid-state synapses
S. Boyn et al ; Nature Comm. 8, 14736 (2017)

See also the Press Release by CNRS (in French), the news piece by Phys.org and the articles in Le Monde and Le Temps.

Tunable spin texture in multiferroic BiFeO3

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Non collinear spin textures such as skyrmions are currently under focus owing to their fundamental interest (associated with the influence of the  topology of the spin configuration on electronic properties) and to their potential for applications in data storage.

Multiferroic BiFeO3 naturally possesses a non collinear spin order which is also controlable by an electric field.  In BiFeO3, spins order along a 62-nm-period cycloid. In our study just out in Advanced Materials, we have shown that when BiFeO3 is grown in thin film form, both epitaxial strain and the application of an external magnetic field lengthen this period and may eventually destroy the cycloidal state. By combining several stimuli (strain, magnetic field, electric field), it thus appears possible to stabilize various non-collinear spin states, which bears a strong potential for spintonics and magnonics.

This work was done in collaboration with the Laboratoire MPQ (Université Paris-Diderot), the GPM (Université de Rouen), the SPMS lab (Ecole Centrale Paris), the ESRF, the ISIS facility and the Moscow Institute of Science and Technology.

Strain and Magnetic Field Induced Spin-Structure Transitions in Multiferroic BiFeO3
A. Agbelele et al, Adv. Mater. 1602327 (2017) ; DOI: 10.1002/adma.201602327

See also the News piece by Labex NanoSaclay (in French).

Mathieu Grisolia defends his PhD thesis

On Monday, September 26, our group member Mathieu Grisolia successfully defended his PhD “Novel interfacial electronic states between correlated insulators“. Exploring novel concepts in correlated oxides was an exciting but arduous task, but Mathieu was certainly up to the challenge. Congratulations !

 

 

Giant spin-charge conversion at oxide interfaces

IREE-sketch.pngThe spin–orbit interaction couples the electrons’ motion to their spin. As a result, a charge current running through a material with strong spin–orbit coupling generates a transverse spin current (spin Hall effect, SHE) and vice versa (inverse spin Hall effect, ISHE). The emergence of SHE and ISHE as charge-to-spin interconversion mechanisms offers a variety of novel spintronic functionalities and devices, some of which do not require any ferromagnetic material. However, the interconversion efficiency of SHE and ISHE (spin Hall angle) is a bulk property that rarely exceeds ten percent, and does not take advantage of interfacial and low-dimensional effects otherwise ubiquitous in spintronic hetero- and mesostructures. In our recent study just out in Nature Materials, we make use of an interface-driven spin–orbit coupling mechanism—the Rashba effect—in the oxide two-dimensional electron system (2DES) LaAlO3/SrTiO3 to achieve spin-to-charge conversion with unprecedented efficiency. Through spin pumping, we inject a spin current from a NiFe film into the oxide 2DES and detect the resulting charge current, which can be strongly modulated by a gate voltage. We discuss the amplitude of the effect and its gate dependence on the basis of the electronic structure of the 2DES and highlight the importance of a long scattering time to achieve ecient spin-to-charge interconversion.

This work was done in collaboration with the Spintec lab (CNRS/Univ. Grenoble Alpes).

Highly efficient and tunable spin to charge conversion through Rashba coupling at oxide interfaces
E. Lesne et al, Nature Mater. 15, 1261 (2016)

See also the News and Views piece by S. Caprara.

1st France-Japan joint Workshop of Oxide Electronics and Spintronics

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The 1st France-Japan joint Workshop of Oxide Electronics and Spintronics took place on May 19 and 20 in Paris and Palaiseau. Organized by Hiroshi Naganuma, an associate professor from Tohoku University and currently a visiting scientist at CNRS/Thales, this event gathered 40 participants from Japan and France to discuss recent results in the field. It was sponsored by the Japanese Society of Applied Physics and CNRS.