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.

Giant topological Hall effect in correlated oxide thin films

CCMO§v2.JPGIn the presence of a perpendicular magnetic field, the trajectory of electrons is curved, which leads to a transverse voltage: this is the Hall effect. When electrons travels through certain types of non-collinear spin textures – such as skyrmions – they also experience the equivalent of a magnetic field, which produces a “topological” Hall effect. In magnetic thin films with perpendicular magnetic anisotropy, magnetization may reverse by the formation of bubbles that in some cases possess a spin structure similar to that of skyrmions. In our recent paper just out in Nature Physics, we have measured a large topological Hall effect in thin films of a weakly doped metallic manganite (Ce,Ca)MnO3. Its parent compound – CaMnO3 – is a Mott insulator, i.e. a material showing an insulating character due to strong repulsion effects between electrons (coined strong correlations). Magnetic force microscopy images reveal the presence of magnetic bubbles whose density shows a magnetic field dependence akin to that of the topological Hall effect. Interestingly, the amplitude of the effect strongly increases as Ce doping is reduced and the materials approaches the Mott insulating state, which suggests that the topological Hall effect is enhanced by strong correlations.

This work was performed in collaboration with Rutgers University, Nagoya University, ICMAB Barcelona and the Universidad Complutense de Madrid

Giant topological Hall effect in correlated oxide thin films
L. Vistoli et al, Nature Phys. doi:10.1038/s41567-018-0307-5 (2018)

See also the News post from our ICMAB collaborators.

Living dead magnetic layer at the surface of a Mott insulator

deadlayerV5.jpg

Rare-earth titanates are Mott insulators, and emerge as promising building blocks to realize exotic electronic states at oxide interfaces. For small rare-earths such as Dy, these titanates are canted ferrimagnets. However, critical to this magnetic order is the 3+ valence of the Ti cations, which is hard to stabilize. In our recent paper just published in Advanced Materials, we report for the first time the growth of high-quality DyTiO3 thin films, with excellent, bulk-like magnetic properties at high thickness, and a surprisingly enhanced saturation magnetization at low thickness. This thickness dependence of the magnetic properties is reminiscent of dead-layer effects in more conventional materials in which magnetization is reduced at low thickness. Through a combination of X-ray spectroscopies and magnetometry we have shown that this “living-dead” magnetic layer arise from uncoupled, paramagnetic Dy ions with neighbouring non-magnetic Ti4+ present at the film surface.

This work was performed in collaboration with the Helmholtz-Zentrum Berlin, the University of Würzburg and the Paul-Scherrer Institute.

A Living-Dead Magnetic Layer at the Surface of Ferrimagnetic DyTiO3 Thin Films
R. Aeschlimann et al ; Adv. Mater. 10.1002/adma.201707489 (2018)

Nanoscale phase-separation mapped in NdNiO3

TOC-NNO-NL.pngThrough a combination of conductive-tip atomic force microscopy (CAFM) and X-ray photemission electron microscopy (XPEEM), we have investigated the phase separation ocurring at the metal-insulator transition of NdNiO3 thin films. Our images reveal the nucleation of ∼100–300 nm metallic domains in the insulating state that grow and percolate as temperature increases. In our paper just out in Nano Letters, we discuss the resistance contrast mechanism, analyze the microscopy and transport data within a percolation model, and propose experiments to harness this mesoscopic electronic texture in devices.

This work was performed in collaboration with the Helmholtz-Zentrum Berlin and the Laboratoire de Physiques des Solides in Orsay.

Direct Mapping of Phase Separation across the Metal–Insulator Transition of NdNiO3
D. Preziosi et al ; Nano Lett. 10.1021/acs.nanolett.7b04728 (2018)

See also the News pieces on Nanotechweb and on the website of Labex NanoSaclay.

Oxide 2-dimensional electron gas growth protocol published as video in JOVE

picJOVEIf you wonder how we perform our experiments and want to delve into the process of growing our oxide samples, you can have a look at this video published as a an article in JOVE, the Journal Of Visualized Experiments. It shows our group member Diogo Vaz growing an heterostructure combining an oxide grown by pulsed laser deposition and a metal deposited by sputtering. The sample is characterized by in-situ X-ray photoelectron spectroscopy to probe the formation of a 2-dimensional electron gas in SrTiO3, and characterized by magnetotransport. The manuscript is available in pdf here.

Growth and electrostatic/chemical phroperties of metal/LaAlO3/SrTiO3 eterostructures
D.C Vaz et al ; J. Vis. Exp. 132,  e56951, doi:10.3791/56951 (2018).

Manuel Bibes receives the Descartes-Huygens award

descartes_huygens.png

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.

Announcement on the University of Gröningen and University of Twente websites.

Pictures from the Award Ceremony that took place on February 20, 2018 at the Académie des Sciences in Paris.

Imaging antiferromagnets with a single spin magnetometer

BFO-NV-site.jpg

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)