Agency: GTR | Branch: EPSRC | Program: | Phase: Research Grant | Award Amount: 329.23K | Year: 2013
Magnetic Materials are employed in an enormous range of applications in modern society, from information storage in computers, refrigeration in security and astronomical instrumentation, biocompatible agents for use as both contrast and polarizing agents in magnetic resonance imaging (MRI) and diagnosis, and as agents for magnetic hyperthermic treatments. Academically, molecule-based magnets are also studied intensively with regard to their important fundamental chemistry and physics, since they have the potential to be exploited in nanoscale electronics devices, as beautifully demonstrated recently by the construction of single-molecule spintronic devices (spin valves and transistors). Molecule-based materials offer the great advantage of being designable and manipulable by synthetic chemistry. That is, they can be constructed atom by atom, molecule by molecule with the unparalled advantages of being soluble, monodisperse in size, shape and physical properties, and tuneable at the atomic scale. Indeed, this bottom-up research vision is not restricted to academia - IBM recently reported information storage in surface-isolated (2x6) arrays of Fe atoms at liquid He temperatures and are actively investigating spintronics and data storage with a view to the ultimate miniaturisation of such technologies. However, before any molecule or molecule-based material can have commercial application or value, the fundamental and intrinsic relationship between structure and magnetic behaviour must be understood. This requires the chemist to design and construct familes of related complexes, characterise them structurally and magnetically, and through extensive collaboration with a network of world-class condensed matter physicists and theoreticians, understand their underlying physical properties. The current proposal directly addresses these fundamental questions through the controlled aggregation and organisation of molecular magnets into designed 0-3D architectures in the solid state. Specifically it applies the fundamental principles underpinning supramolecular chemistry to assemble single-molecule magnets into novel topologies by taking advantage of simple coordination-driven self-assembly processes. We will employ molecular magnets as building blocks for the formation of supramolecular assemblies and coordination polymers in which the spin dynamics of the molecular building blocks are modulated through the attachment of, and interaction with, other paramagnetic moieties. In order to achieve this we will: design and build a range of metalloligands, ranging from simple isotropic molecules to more complex and exotic anisotropic molecules and attach them to pre-made SMMs; construct hybrid magnetic materials from SMMs and cyanometalate building blocks; design and synthesise dual-functioning ligands which are capable of directing the formation of SMMs and simultaneously linking them into higher order (O-3D) materials; and characterise all materials, structurally and magnetically, through a battery of techniques.
Rikken G.L.J.A.,CNRS French National High Magnetic Field Laboratory |
Van Tiggelen B.A.,CNRS Physics and Models in Condensed Media Laboratory
Physical Review Letters | Year: 2012
The Abraham force exerted by a time-dependent electromagnetic field on neutral, polarizable matter has two contributions. The one induced by a time-varying magnetic field and a static electric field is reported here for the first time. We discuss our results in the context of the radiative momentum in matter. Our observations are consistent with Abraham's and Nelson's versions for radiative momentum. © 2012 American Physical Society.
Leboeuf D.,CNRS French National High Magnetic Field Laboratory |
Kramer S.,University of British Columbia |
Hardy W.N.,Canadian Institute for Advanced Research |
Liang R.,Canadian Institute for Advanced Research |
And 3 more authors.
Nature Physics | Year: 2013
The interplay between superconductivity and any other competing order is an essential part of the long-standing debate on the origin of high-temperature superconductivity in cuprate materials1,2. Akin to the situation in the heavy fermions, organic superconductors and pnictides, it has been proposed that the pairing mechanism in the cuprates comes from fluctuations of a nearby quantum phase transition. Recent evidence for charge modulation and its associated fluctuations5-7 in the pseudogap phase of YBa 2Cu3Oy makes charge order a likely candidate for a competing order. However, a thermodynamic signature of the charge-ordering phase transition is still lacking. Moreover, whether the charge modulation is uniaxial or biaxial remains controversial. Here we address both issues by measuring sound velocities in YBa2Cu3O6.55 in high magnetic fields. We provide the first thermodynamic signature of the competing charge-order phase transition in YBa2Cu3O y and construct a field-temperature phase diagram. The comparison of different acoustic modes indicates that the charge modulation is biaxial, which differs from a uniaxial stripe charge order. © 2013 Macmillan Publishers Limited. All rights reserved.
Berciaud S.,CNRS Institute of Genetics and of Molecular and Cellular Biology |
Potemski M.,CNRS French National High Magnetic Field Laboratory |
Faugeras C.,CNRS French National High Magnetic Field Laboratory
Nano Letters | Year: 2014
We probe electronic excitations between Landau levels in freestanding N-layer graphene over a broad energy range, with unprecedented spectral and spatial resolution, using micro magneto-Raman scattering spectroscopy. A characteristic evolution of electronic bands in up to five Bernal-stacked graphene layers is evidenced and shown to remarkably follow a simple theoretical approach, based on an effective bilayer model. (N > 3)-layer graphenes appear as appealing candidates in the quest for novel phenomena, particularly in the quantum Hall effect regime. Our work paves the way toward minimally invasive investigations of magneto-excitons in other emerging low-dimensional systems, with a spatial resolution down to 1 μm. © 2014 American Chemical Society.
Train C.,CNRS French National High Magnetic Field Laboratory |
Train C.,Joseph Fourier University |
Gruselle M.,CNRS Paris Institute of Molecular Chemistry |
Verdaguer M.,CNRS Paris Institute of Molecular Chemistry
Chemical Society Reviews | Year: 2011
In this critical review, it is shown how the introduction of chirality and the control of the absolute configurations of chiral elements in molecular magnets allow obtaining enantiopure chiral magnets (ECM), an archetype of multifunctional materials. This task has been recognised as a major challenge for both chemists and physicists of molecular magnetism. To reach this goal, the former have combined the rational approaches towards molecular-based magnets and of enantiopure metal-organic frameworks. They have used enantiopure stable radicals, ligands from the chiral pool, enantiopure coligands associated with achiral connectors or enantioselective self-assembly to successfully reach their synthetic targets. They were motivated by the will to obtain suitable systems for the experimental demonstration of the influence of enantiomeric purity on the physico-chemical properties. This influence can be found in the magnetic properties themselves but, most interestingly, in the coexistence and interaction between the properties arising from controlled non-centrosymmetry. Thus the combination of natural circular dichroism, second harmonic generation or ferroelectricity with long-range magnetic ordering can give birth to new properties like magneto-chiral dichroism, magnetisation induced second harmonic generation or multiferroicity. The two former synergetic effects have already been demonstrated in enantiopure chiral magnets. The third one remains a challenging target that can be reached by adapting strategies developed towards enantiopure molecular ferroelectrics (119 references). © The Royal Society of Chemistry 2011.
Miyata A.,CNRS French National High Magnetic Field Laboratory |
Mitioglu A.,CNRS French National High Magnetic Field Laboratory |
Plochocka P.,CNRS French National High Magnetic Field Laboratory |
Portugall O.,CNRS French National High Magnetic Field Laboratory |
And 4 more authors.
Nature Physics | Year: 2015
Solar cells based on the organic-inorganic tri-halide perovskite family of materials have shown significant progress recently, offering the prospect of low-cost solar energy from devices that are very simple to process. Fundamental to understanding the operation of these devices is the exciton binding energy, which has proved both difficult to measure directly and controversial. We demonstrate that by using very high magnetic fields it is possible to make an accurate and direct spectroscopic measurement of the exciton binding energy, which we find to be only 16 meV at low temperatures, over three times smaller than has been previously assumed. In the room-temperature phase we show that the binding energy falls to even smaller values of only a few millielectronvolts, which explains their excellent device performance as being due to spontaneous free-carrier generation following light absorption. Additionally, we determine the excitonic reduced effective mass to be 0.104m e (where m e is the electron mass), significantly smaller than previously estimated experimentally but in good agreement with recent calculations. Our work provides crucial information about the photophysics of these materials, which will in turn allow improved optoelectronic device operation and better understanding of their electronic properties. © 2015 Macmillan Publishers Limited. All rights reserved.
Battesti R.,CNRS French National High Magnetic Field Laboratory
Reports on progress in physics. Physical Society (Great Britain) | Year: 2013
In this report we show that a vacuum is a nonlinear optical medium and discuss what the optical phenomena are that should exist in the framework of the standard model of particle physics. We pay special attention to the low energy limit. The predicted effects for photons of energy smaller than the electron rest mass are of such a level that none have yet been observed experimentally. Progress in field sources and related techniques seem to indicate that in a few years vacuum nonlinear optics will be accessible to human investigation.
Battesti R.,CNRS French National High Magnetic Field Laboratory |
Rizzo C.,CNRS French National High Magnetic Field Laboratory
Reports on Progress in Physics | Year: 2013
In this report we show that a vacuum is a nonlinear optical medium and discuss what the optical phenomena are that should exist in the framework of the standard model of particle physics. We pay special attention to the low energy limit. The predicted effects for photons of energy smaller than the electron rest mass are of such a level that none have yet been observed experimentally. Progress in field sources and related techniques seem to indicate that in a few years vacuum nonlinear optics will be accessible to human investigation. © 2013 IOP Publishing Ltd.
Brooks J.S.,CNRS French National High Magnetic Field Laboratory
Chemical Society Reviews | Year: 2010
The purpose of this critical review is twofold: first, to review organic "small molecule" crystalline materials in terms of structure and function; and second, to consider if and how such materials might eventually enter the realm of device applicability. This area, one of the most interdisciplinary fields of research in contemporary materials science, embraces chemistry, physics, engineering, biology, theory and computation. The review therefore attempts to treat a relatively large number of examples including fundamental physical and electronic structure, single component and charge transfer complexes, physical properties of single crystalline materials, thin film and single crystal electronic and photonic devices, functional materials, and bio-inspired structures. The point of view is that of an experimental physicist, and in this context, challenges and possible routes to further advances in the development and utilization of organic small molecule materials are discussed for both fundamental and applied purposes (153 references). © 2010 The Royal Society of Chemistry.
Zhai Y.,CNRS French National High Magnetic Field Laboratory
Cryogenics | Year: 2010
Performance degradation of Nb3Sn cable-in-conduit conductors (CICCs) is a critical issue in large-scale magnet design such as the International Thermonuclear Experimental Reactor (ITER) and the series-connected hybrid (SCH) magnets currently under development at the National High Magnetic Field Laboratory (NHMFL). Not only the critical current is significantly lower than expectations but also the voltage-current characteristic is observed to have a much broader transition from a single strand to a CICC cable. The variation of conductor voltage-current characteristic as a result of cable electromagnetic, mechanical and thermal interactions is challenging to model. In this paper, we use a new numerical model, called the Florida electro-mechanical cable model (FEMCAM) benchmarked against 40 different conductor tests, to study the influence of bending strain and current non-uniformity on the critical current and n-value of Nb3Sn strands and CICC cables. The new model combines thermal bending effects during cool-down, electromagnetic bending effects during magnet operation and current transfer in strands with filament fracture. The n-value of a strand under bending is derived from integration of filament critical current over strand cross-section for full and no current transfer. The cable n-value is obtained from the power law relation of cable electric field and critical current curve. By comparing numerical results with measurements of advanced Nb3Sn strands and various CICC cables, we demonstrate that FEMCAM is self-consistent in modeling inter-filament current transfer. The new model predicts that Ic degradation of bent strands initially follows closely full current transfer but starts deviating and falls between full and no current transfer with an increasing bending strain. The results agree with recent TARSIS measurements for less than 1% bending strain mostly interested in practice. The strand n-value degradation from FEMCAM with no filament current transfer agrees better with measurements than that from full current transfer. Finally, FEMCAM simulated cable n-values are compared with various CICC measurements. The results imply that FEMCAM is a useful tool for the design of Nb3Sn-based CICCs and both thermal bending and electromagnetic bending play important roles in CICC performance. © 2009 Elsevier Ltd. All rights reserved.