La réunion annuelle des plateformes régionales de nanofabrication du Grand Est aura lieu le 13 novembre 2018 à 9h30 à l’amphithéâtre Grunewald (bâtiment 25).

Des présentations scientifiques fortement liées à la nanofabrication seront données par des chercheurs de l’Institut Jean Lamour (Nancy), de l’Institut Charles Delaunay (Troyes), de Icube et de l’IPCMS.

contact: hicham.majjad@ipcms.unistra.fr

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Designing with spins: nanomagnonics with engineered spin-textures

Edoardo Albisetti

City University of New York &  Politecnico di Milano

The control of spin-waves holds the promise to enable energy-efficient computing. [1] However, controlling spin-waves at the nanoscale, which is crucial for the realization of magnonic nanodevices, is extremely challenging due to the difficulty in controlling the nanoscopic magnetic properties via conventional nanofabrication techniques. We recently demonstrated a new technique for creating reconfigurable magnonic structures by performing a highly localized field cooling with the hot tip of a scanning probe microscope, in an exchange bias bilayer. In such structures, the spin-wave excitation and propagation can be spatially controlled with no need for external fields. [2,3]

By controlling the patterning geometry and external magnetic field direction, we demonstrate a strategy for stabilizing complex multidimensional spin-textures ranging from 2D domains with tailored spin-configuration, to straight and curved 1D magnetic domain walls, to 0D tailored topological solitons such as vortices and Bloch lines with deterministically controlled chirality, position and vorticity. [4]

We show that such engineered spin-textures can be used effectively as waveguides and sources of propagating spin-waves. In particular we demonstrate the channeling and steering of propagating spin-waves in arbitrarily shaped nanomagnonic waveguides based on straight and curved domain walls, and a prototypic nanomagnonic circuit based on two converging waveguides, allowing for the tunable spatial superposition and interaction of confined spin-waves modes. [5] Finally, we show that, by patterning nanoscale spin-textures in an exchange biased synthetic antiferromagnet (SAF), it is possible to create spatially shaped propagating wave fronts with linear and radial geometry, and to control the interference of short-wavelength spin-waves. [6]

The ability to control magnons via nanoscale-designed spin-textures opens up a plethora of exciting possibilities for the realization of energy-efficient reconfigurable computing platforms.

Modulation de l’anisotropie dans le ferrite de cobalt en couches minces pour des applications en électronique de spin

Elodie MARTIN

IPCMS – DCMI

Directeur de thèse : Christophe Lefèvre

“Colloidal liquid crystal of inorganic nanosheets”

Dr. Nobuyoshi MIYAMOTO

Research Director of Materials and Energy Device Research Center
Fukuoka Institute of Technology (FIT-ME)
Fukuoka, JAPAN

“Magnetic and electronic properties of the two-dimensional electron gas at the LaAlO₃/SrTiO₃ interfaces”

Marco SALLUZZO

CNR-SPIN

The quasi two-dimensional electron gas (q2DEG) created at the interface between LaAlO₃ and SrTiO₃ have attracted strong interest in recent years. This system shows an intriguing inversion of the Ti3d bands hierarchy at the interface respect the bulk [1], and some reports even suggested a coexistence between ferromagnetism and superconductivity [2-4]. More recently, a q2DEG have been observed also at the bare surface of SrTiO₃ [5]. Spin-resolved ARPES experiments performed on in-situ prepared STO (001) surfaces have revealed that the surface state exhibits a giant Rashba-like spin-orbit characterized by a broken Kramers-degeneracy at k = 0, which implies the existence of some unknown magnetic order [6] In this talk I will present an overview of the electronic and magnetic properties of the q2DEG formed at titanate surfaces interfaces, investigated by synchrotron radiation based x-ray spectroscopy techniques. We find a sizable Ti-3d¹ magnetic moment at the surface of (001) SrTiO₃ surface and at the LaAlO₃/SrTiO₃ (001) interfaces containing oxygen vacancies.  However, the magnetic moment is quenched in LAO/STO by annealing in oxygen, while it is extremely small in the case of (001) STO surface prepared in ultrahigh vacuum at temperatures lower than 250°C.  This result, implies an important role of oxygen vacancies in the magnetism of these oxide surfaces/interfaces [7,8]. A ferromagnetic ground state is, on the other hand, stabilized even in optimally oxidized conducting interfaces by inserting 2 unit cells of delta-doping EuTiO₃ between LAO and STO. We find that the EuTiO₃ thin layer is ferromagnetic, instead of being antiferromagnetic as in the bulk, due to the ordering of Eu²⁺ spin mediated by itinerant carriers. The exchange interaction between Eu²⁺ and Ti3d¹-electrons in both ETO and STO interfacial layers give rise to a very large ordered Ti-magnetic moment and to a spin-polarization of the Ti-3d-bands.

References

[8] D. Stornaiuolo, Nature Materials 15, 278–283 (2016)

“Dielectric optically-active metamaterials: are they achievable through bottom-up chemistry ?”

Glenna L. Drisko

CNRS researcher
ICMCB – UMR5026
Bordeaux

The advent of metamaterials consisted of a flurry of activity around plasmonic resonators. Fifteen years of research has confirmed that plasmonic-based materials absorb too much light to be used in optically-active metamaterials. High refractive index materials theoretically provide an alternative to plasmonics. Semiconductors boast the highest refractive index across the visible spectrum among naturally occurring materials. Silicon is generally favored for optical applications due to its natural abundance, omnipresence in the electronics industry, and relatively easy synthesis compared to other semiconductors. However, even silicon is extremely difficult to fabricate using bottom-up chemistry. It is relatively easy to produce 10 nm silicon particles, however these are too small for optically-active meta-atoms and such small particles oxidize completely to low-refractive index SiO2. This begs asking, what silicon forms can we realistically expect to produce? And are there alternatives to silicon?

Metamaterials produced via bottom-up synthesis methods require the preparation of individual resonant particles, referred to as meta-atoms, and then the assembly of these particles into a 2D or 3D material. My group has approached the synthesis of silicon meta-atoms by examining the effect of the nature of the solvent, silicon precursor, reducing agent and processing conditions on the silicon particle diameter, polydispersity and crystallinity. Through these lessons, we have come closer to ideal silicon meta-atoms. We have also begun research into less optically fantastic, but more easily obtained TiO2 nanoparticles. I will present the synthesis methods, optical measurements and future prospects of these dielectric meta-atoms. I will also present the plasmonic-based metamaterials produced previously in the team, to showcase what can be achieved using bottom-up chemistry.

“Nanodevices for Bio-inspired Computing”

Julie GROLLIER

CNRS/Thales, Palaiseau, France

In the last five years, Artificial Intelligence has made striking progress, now defeating humans at subtle strategy games, such as Go, and even Poker. However, these algorithms are running on traditional processors which have a radically different architecture than the biological neural networks they are inspired from. This considerably slows them down and requires massive amounts of electrical power, more than ten thousand times what the brain typically needs to function. This energy dissipation is not only becoming an environmental issue, but it also sets a limit to the size of neural networks that can be simulated. We are at a point where we need to rethink the way we compute, and build hardware chips directly inspired from the architecture of the brain. This is a challenge. Indeed, contrarily to current electronic systems, the brain is a huge parallel network closely entangling memory and processing.
In this talk, I will show that, for building the neuromorphic chips of the future, we will need to emulate functionalities of synapses and neurons at the nanoscale. I will review the recent developments of memristive nano-synapses and oscillating nano-neurons, the physical mechanisms at stake, and the challenges in terms of materials. Finally, I will present the first achievements of neuromorphic computing with novel nanodevices and the fascinating perspectives of this emerging field.