Stéphane Fusil

Bio: Stéphane Fusil is an academic researcher from Université Paris-Saclay. The author has contributed to research in topics: Ferroelectricity & Multiferroics. The author has an hindex of 47, co-authored 106 publications receiving 11647 citations. Previous affiliations of Stéphane Fusil include University of Paris & Centre national de la recherche scientifique.

Tunnel junctions with multiferroic barriers

Abstract: Multiferroics are singular materials that can exhibit simultaneously electric and magnetic orders. Some are ferroelectric and ferromagnetic and provide the opportunity to encode information in electric polarization and magnetization to obtain four logic states. However, such materials are rare and schemes allowing a simple electrical readout of these states have not been demonstrated in the same device. Here, we show that films of La0.1Bi0.9MnO3 (LBMO) are ferromagnetic and ferroelectric, and retain both ferroic properties down to a thickness of 2 nm. We have integrated such ultrathin multiferroic films as barriers in spin-filter-type tunnel junctions that exploit the magnetic and ferroelectric degrees of freedom of LBMO. Whereas ferromagnetism permits read operations reminiscent of magnetic random access memories (MRAM), the electrical switching evokes a ferroelectric RAM write operation. Significantly, our device does not require the destructive ferroelectric readout, and therefore represents an advance over the original four-state memory concept based on multiferroics.

A ferroelectric memristor

Abstract: Memristors are devices whose dynamic properties are of interest because they can mimic the operation of biological synapses. The demonstration that ferroelectric domains in tunnel junctions behave like memristors suggests new approaches for designing neuromorphic circuits.

Giant tunnel electroresistance for non-destructive readout of ferroelectric states

Abstract: Ferroelectrics possess a polarization that is spontaneous, stable and electrically switchable, and submicrometre-thick ferroelectric films are currently used as non-volatile memory elements with destructive capacitive readout. Memories based on tunnel junctions with ultrathin ferroelectric barriers would enable non-destructive resistive readout. However, the achievement of room-temperature polarization stability and switching at very low thickness is challenging. Here we use piezoresponse force microscopy at room temperature to show robust ferroelectricity down to 1 nm in highly strained BaTiO(3) films; we also use room-temperature conductive-tip atomic force microscopy to demonstrate resistive readout of the polarization state through its influence on the tunnel current. The resulting electroresistance effect scales exponentially with ferroelectric film thickness, reaching approximately 75,000% at 3 nm. Our approach exploits the otherwise undesirable leakage current-dominated by tunnelling at these very low thicknesses-to read the polarization state without destroying it. We demonstrate scalability down to 70 nm, corresponding to potential densities of >16 Gbit inch(-2). These results pave the way towards ferroelectric memories with simplified architectures, higher densities and faster operation, and should inspire further exploration of the interplay between quantum tunnelling and ferroelectricity at the nanoscale.

Ferroelectric Control of Spin Polarization

Abstract: A current drawback of spintronics is the large power that is usually required for magnetic writing, in contrast with nanoelectronics, which relies on "zero-current," gate-controlled operations. Efforts have been made to control the spin-relaxation rate, the Curie temperature, or the magnetic anisotropy with a gate voltage, but these effects are usually small and volatile. We used ferroelectric tunnel junctions with ferromagnetic electrodes to demonstrate local, large, and nonvolatile control of carrier spin polarization by electrically switching ferroelectric polarization. Our results represent a giant type of interfacial magnetoelectric coupling and suggest a low-power approach for spin-based information control.

Room-temperature coexistence of large electric polarization and magnetic order in Bi Fe O 3 single crystals

Abstract: From an experimental point of view, room-temperature ferroelectricity in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ is raising many questions. Electric measurements made a long time ago on solid solutions of $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ with $\mathrm{Pb}(\mathrm{Ti},\mathrm{Zr}){\mathrm{O}}_{3}$ indicate that a spontaneous electric polarization exists in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ below the Curie temperature ${T}_{C}=1143\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Yet in most reported works, the synthesized samples are too conductive at room temperature to get a clear polarization loop in the bulk without any effects of extrinsic physical or chemical parameters. Surprisingly, up to now there has been no report of a $P(E)$ (polarization versus electric field) loop at room temperature on single crystals of $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$. We describe here our procedure to synthesize ceramics and to grow good quality sizeable single crystals by a flux method. We demonstrate that $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ is indeed ferroelectric at room temperature through evidence by piezoresponse force microscopy and $P(E)$ loops. The polarization is found to be large, around $60\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{C}∕{\mathrm{cm}}^{2}$, a value that has only been reached in thin films. Magnetic measurements using a superconducting quantum interference device magnetometer and M\"ossbauer spectroscopy are also presented. The latter confirms the results of nuclear magnetic resonance measurements concerning the anisotropy of the hyperfine field attributed to the magnetic cycloidal structure.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Multiferroic and magnetoelectric materials

Abstract: A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few 'multiferroic' materials that exhibit both of these properties, but the 'magnetoelectric' coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, there has been a recent resurgence of interest driven by long-term technological aspirations.

Physics and Applications of Bismuth Ferrite

Abstract: BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

Multiferroics: progress and prospects in thin films.

Abstract: Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties — and in turn promise new device applications — as a result of the coupling between their dual order parameters. We review recent progress in the growth, characterization and understanding of thin-film multiferroics. The availability of high-quality thin-film multiferroics makes it easier to tailor their properties through epitaxial strain, atomic-level engineering of chemistry and interfacial coupling, and is a prerequisite for their incorporation into practical devices. We discuss novel device paradigms based on magnetoelectric coupling, and outline the key scientific challenges in the field.

Memristive devices for computing

Abstract: Memristive devices are electrical resistance switches that can retain a state of internal resistance based on the history of applied voltage and current. These devices can store and process information, and offer several key performance characteristics that exceed conventional integrated circuit technology. An important class of memristive devices are two-terminal resistance switches based on ionic motion, which are built from a simple conductor/insulator/conductor thin-film stack. These devices were originally conceived in the late 1960s and recent progress has led to fast, low-energy, high-endurance devices that can be scaled down to less than 10 nm and stacked in three dimensions. However, the underlying device mechanisms remain unclear, which is a significant barrier to their widespread application. Here, we review recent progress in the development and understanding of memristive devices. We also examine the performance requirements for computing with memristive devices and detail how the outstanding challenges could be met.