research highlights MOLECULAR ORGANIC FRAMEWORKS The proposed van der Waals sf-MTJ short dialkyne, the only product of the reaction is a mono-triazole. This is because device consists of a thin bilayer, trilayer Selectivity in one click or four-layer CrI tunnel barrier sandwiched the dialkyne is shorter than the distance J. Am. Chem. Soc. http://doi.org/cpz7 (2018) between the azides. When using a longer between few-layer graphene and hexagonal boron nitride. In each case, CrI acts as a dialkyne, the researchers find a mixture of products including a bis-triazole. Finally, spin filter in which the spin orientation of constituent layers can be tuned by a to release the product, they add methyl bromide, which displaces the alkyne- magnetic field, creating multiple magnetic states of thickness-dependent complexity. functionalized triazole and regenerates the Br initial Mn-based MOF. The tunnelling current in the sf-MTJs is MeBr highly sensitive to the net spin polarization All reactions are in the solid state and the crystallinity of the MOF is maintained in CrI and can be greatly enhanced in the Represents Mn(I) sites bound sample with fully aligned magnetization. b throughout the process, thus providing to the parent framework researchers with a reliable ruler to control The effect is especially pronounced in Credit: American Chemical Society a four-layer CrI that shows TMR of the selectivity of the reaction. AM up to 19,000% for a magnetic field of https://doi.org/10.1038/s41565-018-0173-4 9 T at 2 K. OB It is notoriously difficult to react only one alkyne moiety of a symmetric dialkyne https://doi.org/10.1038/s41565-018-0175-2 2D MAGNEtISM with an azide, as both alkynes are likely to undergo a [3+ 2] cycloaddition reaction Memory mille feuille MAGNEtIC RESONANCE IMAGING (a click-chemistry reaction) and form a Science http://doi.org/cpz8 (2018) bis-triazole. As a result, lengthy chemical Nat. Commun. 9, 1776 (2018) protection and deprotection procedures The promise of low power consumption have been developed. Now, Huxley et al. combined with the continued scaling of its Magnetic resonance imaging (MRI) is a have reported a direct synthetic strategy to components to higher density could see widely known medical imaging technique convert a symmetric dialkyne into an alkyne- magnetoresistive random-access memory for diagnostics. However, its application functionalized triazole by taking advantage (MRAM) become a dominant type of in battery characterization is greatly of the steric constrains that a metal–organic memory technology in the foreseeable limited due to the reliance of MRI on framework (MOF), used as a nanovessel, future. To this end, the recent discovery radiofrequency penetration, which can be imposes on the reaction pathway. of 2D magnetism in chromium triiodide easily impeded by the conductive enclosures The researchers first prepare a Mn-based (CrI ) creates opportunities for realizing in commercial cells. Now, Jerschow MOF in which the Mn atoms are about 13 atomically thin magnetic devices. and co-workers employ MRI to non- Å apart. They then substitute the bromine To further illustrate this point, Song et al. destructively identify the state of charges atoms, which are attached to each Mn, have now reported layer-dependent and defects in a rechargeable lithium-ion cell with an azide moiety, therefore creating tunnelling magnetoresistance (TMR) in without need for disassembly. an environment in which the azides are a multiple-spin-filter magnetic tunnel This is achieved by measuring permanent uniformly spaced within the pores of the junction (sf-MTJ) based on a 2D magnetic and small induced magnetic field changes MOF. When reacting the MOF with a insulator CrI . using magnetic resonance methods. The magnetic susceptibility χ is material dependent and changes due to variation of the oxidation states of the anode and QUANtUM Phy SICS cathode materials during charge/discharge Spinning the spin Sci. Adv. 4, eaar7691 (2018) cycles. The researchers map the evolution of the magnetic field distribution over the Rotating a quantum system at high frequencies opens a window to fundamental cycles. By matching the magnetic field aspects of quantum mechanics, such as rotationally induced geometric phases, strain changes to the levels of charge, they can or magnetic fields. Yet, to initialize, control and readout a single quantum system in extract the magnetic susceptibility and a rotating frame is challenging. Wood and co-workers now explore single nitrogen- information about the state of charge. Aside vacancy (NV) centres in diamond spinning at high frequency and, by means of from examining the state of the lithium- spin-echo interferometry, detect a modulation of the Zeeman shift induced by a ion cell over time, MRI is also capable of 200,000 r.p.m. rotation of the spin qubit. assessing the quality of the cell. It is very To track a single NV centre during the fast rotation, the researchers mounted the sensitive and thus not only identifies the diamond onto a rotor and inserted it together with a microwave wire into a confocal flaws but also probes reproducibility of scanning microscope. For the stroboscope-like experiments, they then synchronize the cell construction. The MRI method the laser initialization of the spin qubit, its manipulation with microwave pulses, and for diagnosing remaining charge and the phase of the qubit rotation. As a proof-of-principle, a single NV centre serves cell health can come in handy in as a rotating frame quantum sensor. A slightly misaligned magnetic field induces a manufacturing processes. WS modulated Zeeman splitting in the rotating spin qubit. Employing a spin-echo pulse sequence, the scientists measure the effective field modulation and determine the https://doi.org/10.1038/s41565-018-0176-1 misalignment of the field with respect to the rotational axis. BH Olga Bubnova, Benjamin Heinrich, https://doi.org/10.1038/s41565-018-0174-3 Alberto Moscatelli and Wenjie Sun NAtURE NANO tEChNOLOG y | VOL 13 | JUNE 2018 | 436 | www.nature.com/naturenanotechnology © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Nature Nanotechnology – Springer Journals
Published: Jun 6, 2018
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