Magnetoelastic effects and random magnetic anisotropy in highly strained ultrathin Ni nanowires epitaxied in a SrTiO3 matrix

International audienceWe analyze the magnetic anisotropy of Ni nanowires with diameters smaller than 5 nm. The nanowires are vertically epitaxied in a SrTiO 3 (001) matrix which generates huge tensile strains up to 3.6% along the nanowire axis. This leads to an unusual anisotropy, characterized by an easy magnetization plane perpendicular to the nanowire axis. Hysteresis cycles M(H) unveil an overall in-plane isotropy, while an opening of the M(H) cycles and thermal activation measurements indicate the presence of local energy barriers inside the nanowires. Surprisingly, the coercive field H c (T) decays exponentially with increasing temperature, for both the easy plane and the hard axis. Based on these findings, we provide an analysis of magnetoelastic effects in the nanowires. By considering global averaging over the anisotropy distribution and local averaging according to the Random Magnetic Anisotropy model, we find that the global anisotropy, with its hard axis and isotropic easy plane, is related to the mean strain, while coercivity arises from local strain variations. We evidence that a thermally activated anisotropy softening occurs in the nanowires, in addition to Sharrock's law of thermal reduction of coercivity. Possible mechanisms responsible for this thermal softening of anisotropy are proposed and discussed. Our study eventually allows to identify two major competing effects at play in the present system: an increasing magnetic anisotropy with increasing strain and a reduction of the anisotropy with increasing local strain fluctuations

Phase separation and surface segregation in Co – Au – SrTiO3 thin films: Self-assembly of bilayered epitaxial nanocolumnar composites

International audiencePhase separation and surface segregation are powerful levers that allow to synthesize nanocompos-ites via self-assembly. In the present work, we combine these concepts with 3-dimensional vertical epitaxial growth and study Co-Au-SrTiO3 thin films as a model system. We demonstrate that SrTiO3, Co and Au undergo phase separation during sequential pulsed laser deposition, giving rise to a dense array of ultrathin bilayered Co-Au nanowires (NWs) with highly anisotropic optical and magnetic properties. A detailed analysis of the structural properties of the embedded metallic NWs reveals stabilization of a Co fcc phase and pronounced coupling to the matrix, which leads to large magnetoelastic effects. We discuss possible growth mechanisms yielding bilayer phase separation in nanocolumnar composites and show how the present results can be used to estimate a lower bound for the Co/Au interface energy

Reducing STEM gender bias with VIDS (video interventions for diversity in STEM)

Gender biases contribute to the underrepresentation of women in STEM. In response, the scientific community has called for methods to reduce bias, but few validated interventions exist. Thus, an interdisciplinary group of researchers and filmmakers partnered to create VIDS (Video Interventions for Diversity in STEM), which are short videos that expose participants to empirical findings from published gender bias research in 1 of 3 conditions. One condition illustrated findings using narratives (compelling stories), and the second condition presented the same results using expert interviews (straightforward facts). A hybrid condition included both narrative and expert interview videos. Results of two experiments revealed that relative to controls, VIDS successfully reduced gender bias and increased awareness of gender bias, positive attitudes toward women in STEM, anger, empathy, and intentions to engage in behaviors that promote gender parity in STEM. The narratives were particularly impactful for emotions, while the expert interviews most strongly impacted awareness and attitudes. The hybrid condition reflected the strengths of both the narratives and expert interviews (though effects were sometimes slightly weaker than the other conditions). VIDS produced substantial immediate effects among both men and women in the general population and STEM faculty, and effects largely persisted at follow-up. (PsycINFO Database Record (c) 2018 APA, all rights reserved

Atomic-Scale Study of Metal–Oxide Interfaces and Magnetoelastic Coupling in Self-Assembled Epitaxial Vertically Aligned Magnetic Nanocomposites

Vertically aligned nanocomposites (VANs) of metal/oxide type have recently emerged as a novel class of heterostructures with great scientific and technological potential in the fields of nanomagnetism, multiferroism, and catalysis. One of the salient features of these hybrid materials is their huge vertical metal/oxide interface, which plays a key role in determining the final magnetic and/or transport properties of the composite structure. However, in contrast to their well‐studied planar counterparts, detailed information on the structural features of vertical interfaces encountered in VANs is scarce. In this work, high resolution scanning transmission electron microscopy (STEM) and electron energy‐loss spectroscopy (EELS) are used to provide an element selective atomic‐scale analysis of the interface in a composite consisting of ultrathin, self‐assembled Ni nanowires, vertically epitaxied in a SrTiO3/SrTiO3(001) matrix. Spectroscopic EELS measurements evidence rather sharp interfaces (6–7 Å) with the creation of metallic NiTi bonds and the absence of nickel oxide formation is confirmed by X‐ray absorption spectroscopy measurements. The presence of these well‐defined phase boundaries, combined with a large lattice mismatch between the oxide and metallic species, gives rise to pronounced magnetoelastic effects. Self‐assembled columnar Ni:SrTiO3 composites thus appear as ideal model systems to explore vertical strain engineering in metal/oxide nanostructures

Improving the sensitivity of future GW observatories in the 1-10 Hz band: Newtonian and seismic noise

The next generation gravitational wave interferometric detectors will likely be underground detectors to extend the GW detection frequency band to frequencies below the Newtonian noise limit. Newtonian noise originates from the continuous motion of the Earth’s crust driven by human activity, tidal stresses and seismic motion, and from mass density fluctuations in the atmosphere. It is calculated that on Earth’s surface, on a typical day, it will exceed the expected GW signals at frequencies below 10 Hz. The noise will decrease underground by an unknown amount. It is important to investigate and to quantify this expected reduction and its effect on the sensitivity of future detectors, to plan for further improvement strategies. We report about some of these aspects. Analytical models can be used in the simplest scenarios to get a better qualitative and semi-quantitative understanding. As more complete modeling can be done numerically, we will discuss also some results obtained with a finite-element-based modeling tool. The method is verified by comparing its results with the results of analytic calculations for surface detectors. A key point about noise models is their initial parameters and conditions, which require detailed information about seismic motion in a real scenario. We will describe an effort to characterize the seismic activity at the Homestake mine which is currently in progress. This activity is specifically aimed to provide informations and to explore the site as a possible candidate for an underground observatory. Although the only compelling reason to put the interferometer underground is to reduce the Newtonian noise, we expect that the more stable underground environment will have a more general positive impact on the sensitivity.We will end this report with some considerations about seismic and suspension noise

A double-sided, shield-less stave prototype for the ATLAS upgrade strip tracker for the high luminosity LHC

A detailed description of the integration structures for the barrel region of the silicon strips tracker of the ATLAS Phase-II upgrade for the upgrade of the Large Hadron Collider, the so-called High Luminosity LHC (HL-LHC), is presented. This paper focuses on one of the latest demonstrator prototypes recently assembled, with numerous unique features. It consists of a shortened, shield-less, and double sided stave, with two candidate power distributions implemented. Thermal and electrical performances of the prototype are presented, as well as a description of the assembly procedures and tools

Sensitivity Studies for Third-Generation Gravitational Wave Observatories

Advanced gravitational wave detectors, currently under construction, are expected to directly observe gravitational wave signals of astrophysical origin. The Einstein Telescope, a third-generation gravitational wave detector, has been proposed in order to fully open up the emerging field of gravitational wave astronomy. In this article we describe sensitivity models for the Einstein Telescope and investigate potential limits imposed by fundamental noise sources. A special focus is set on evaluating the frequency band below 10Hz where a complex mixture of seismic, gravity gradient, suspension thermal and radiation pressure noise dominates. We develop the most accurate sensitivity model, referred to as ET-D, for a third-generation detector so far, including the most relevant fundamental noise contributions.Comment: 13 pages, 7 picture

Reducing STEM gender bias with VIDS (video interventions for diversity in STEM)

Gender biases contribute to the underrepresentation of women in STEM. In response, the scientific community has called for methods to reduce bias, but few validated interventions exist. Thus, an interdisciplinary group of researchers and filmmakers partnered to create VIDS (Video Interventions for Diversity in STEM), which are short videos that expose participants to empirical findings from published gender bias research in 1 of 3 conditions. One condition illustrated findings using narratives (compelling stories), and the second condition presented the same results using expert interviews (straightforward facts). A hybrid condition included both narrative and expert interview videos. Results of two experiments revealed that relative to controls, VIDS successfully reduced gender bias and increased awareness of gender bias, positive attitudes toward women in STEM, anger, empathy, and intentions to engage in behaviors that promote gender parity in STEM. The narratives were particularly impactful for emotions, while the expert interviews most strongly impacted awareness and attitudes. The hybrid condition reflected the strengths of both the narratives and expert interviews (though effects were sometimes slightly weaker than the other conditions). VIDS produced substantial immediate effects among both men and women in the general population and STEM faculty, and effects largely persisted at follow-up. (PsycINFO Database Record (c) 2018 APA, all rights reserved

Scientific Objectives of Einstein Telescope

The advanced interferometer network will herald a new era in observational astronomy. There is a very strong science case to go beyond the advanced detector network and build detectors that operate in a frequency range from 1 Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors will be able to probe a range of topics in nuclear physics, astronomy, cosmology and fundamental physics, providing insights into many unsolved problems in these areas.Comment: 18 pages, 4 figures, Plenary talk given at Amaldi Meeting, July 201