Showing papers by "Stéphane Fusil published in 2009"

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.

Evidence for room-temperature multiferroicity in a compound with a giant axial ratio.

Abstract: In the search for multiferroic materials magnetic compounds with a strongly elongated unit-cell (large axial ratio $c/a$) have been scrutinized intensely However, none was hitherto proven to have a switchable polarization, an essential feature of ferroelectrics Here, we provide evidence for the epitaxial stabilization of a monoclinic phase of ${\mathrm{BiFeO}}_{3}$ with a giant axial ratio ($c/a=123$) that is both ferroelectric and magnetic at room temperature Surprisingly, and in contrast with previous theoretical predictions, the polarization does not increase dramatically with $c/a$ We discuss our results in terms of the competition between polar and antiferrodistortive instabilities and give perspectives for engineering multiferroic phases

Phase-locking of magnetic vortices mediated by antivortices.

Abstract: Synchronized spin-valve oscillators may lead to nanosized microwave generators that do not require discrete elements such as capacitors or inductors. Uniformly magnetized oscillators have been synchronized, but offer low power. Gyrating magnetic vortices offer greater power, but vortex synchronization has yet to be demonstrated. Here we find that vortices can interact with each other through the mediation of antivortices, leading to synchronization when they are closely spaced. The synchronization does not require a magnetic field, making the system attractive for electronic device integration. Also, because each vortex is a topological soliton, this work presents a model experimental system for the study of interacting solitons.

Towards Two-Dimensional Metallic Behavior at LaAlO 3 / SrTiO 3 Interfaces

Abstract: Using a low-temperature conductive-tip atomic force microscope in cross-section geometry we have characterized the local transport properties of the metallic electron gas that forms at the interface between ${\mathrm{LaAlO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$. At low temperature, we find that the carriers do not spread away from the interface but are confined within $\ensuremath{\sim}10\text{ }\text{ }\mathrm{nm}$, just like at room temperature. Simulations taking into account both the large temperature and electric-field dependence of the permittivity of ${\mathrm{SrTiO}}_{3}$ predict a confinement over a few nm for sheet carrier densities larger than $\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$. We discuss the experimental and simulations results in terms of a multiband carrier system. Remarkably, the Fermi wavelength estimated from Hall measurements is $\ensuremath{\sim}16\text{ }\text{ }\mathrm{nm}$, indicating that the electron gas in on the verge of two dimensionality.

Anisotropic magneto-Coulomb effects and magnetic single-electron-transistor action in a single nanoparticle

Abstract: Anisotropies in the response of ferromagnetic electrodes attached to a gold nanoparticle lead to Coulomb blockade and spin-valve-like magnetoresistance phenomena. Such behaviour could allow the development of magnetically gated single-electron transistors composed of just two terminals.

Study of atomic force microscopy nanoindentation for the development of nanostructures

Abstract: We have studied the fabrication of atomic force microscope (AFM) based nanotemplates using electrically controlled indentation (ECI) and a composite barrier (photoresist/alumina) that is resistant to the lithography process and presents good mechanical properties for indentation. The indentation process is affected by several factors such as the indentation speed, the trigger voltage and the barrier type. We have used the nanotemplate technique to fabricate small gold–gold nanocontacts (1–10 nm). In this limit, the size of the contacts that is obtained through the indentation process seems to be stochastic. However, low dimension, clean metallic contacts were achieved with high temporal stability and compatible with low temperature measurements. The fabricated nanotemplates are versatile and can be used in a wide range of applications, from nanojunctions to connecting a single nano-object. Small area metallic contacts can be used to study spin injection or ballistic transport.