Spintronics based random access memory: a review Bhatti, Sabpreet; Sbiaa, Rachid; Hirohata, Atsufumi ...
Materials today (Kidlington, England),
November 2017, 2017-11-00, Letnik:
20, Številka:
9
Journal Article
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This article reviews spintronics based memories, in particular, magnetic random access memory (MRAM) in a systematic manner. Debuted as a humble 4Mb product by FreeScale in 2006, the ...MRAM has grown to a 256Mb product of Everspin in 2016. During this period, MRAM has overcome several hurdles and have reached a stage, where the potential for MRAM is very promising. One of the main hurdles that the MRAM overcome between 2006 and 2016 is the way the information is written. The 4Mb MRAM used a magnetic field based switching technology that would be almost impossible to scale below 100nm. The 256Mb MRAM, on the other hand uses a different writing mechanism based on Spin Transfer Torque (STT), which is scalable to very low dimensions. In addition to the difference in the writing mechanism, there has also been a major shift in the storage material. Whereas the 4Mb MRAM used materials with in-plane magnetic anisotropy, the 256Mb MRAM uses materials with a perpendicular magnetic anisotropy (PMA). MRAM based on PMA is also scalable to much higher densities.
The paper starts with a brief history of memory technologies, followed by a brief description of the working principles of MRAM for novice. Reading information from MRAM, the technologies, materials and the physics behind reading of bits in MRAM are described in detail. As a next step, the physics and technologies involved in writing information are described. The magnetic field based writing and its limitations are described first, followed by an explanation of STT mechanism. The materials and physics behind storage of information is described next. MRAMs with in-plane magnetization, their layered material structure and the disadvantages are described first, followed by the advantages of MRAMs with perpendicular magnetization, their advantages etc. The technologies to improve writability and potential challenges and reliability issues are discussed next. Some of the future technologies that might help the industry to move beyond the conventional MRAM technology are discussed at the end of the paper, followed by a summary and an outlook.
Peptoid polymers are often crystalline in the solid-state as examined by X-ray scattering, but thus far, there has been no attempt to identify a common structural motif among them. In order to probe ...the relationship between molecular structure and crystal structure, we synthesized and analyzed a series of crystalline peptoid copolymers, systematically varying peptoid side-chain length (S) and main-chain length (N). We also examined X-ray scattering data from 18 previously reported peptoid polymers. In all peptoids, we found that the unit cell dimensions, a, b, and c, are simple functions of S and N: a (Å) = 4.55, b (Å) = 2.98N + 0.35, and c (Å) = 1.86S + 5.5. These relationships, which apply to both bulk crystals and self-assembled nanosheets in water, indicate that the molecules adopt extended, planar conformations. Furthermore, we performed molecular dynamics simulations (MD) of peptoid polymer lattices, which indicate that all backbone amides adopt the cis conformation. This is a surprising conclusion, because previous studies on isolated molecules indicated an energetic preference for the trans conformer. This study demonstrates that when packed into supramolecular lattices or crystals, peptoid polymers prefer to adopt a regular, extended, all-cis secondary structure.
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Electrocatalytic hydrogen evolution reaction (HER) in alkaline environments is one of the major energy conversion processes in water electrolysis technology. Very active and ...cost-effective catalysts are highly desirable for alkaline HER not only for its industrial value but also for its fundamental importance in studying all electrocatalytic reactions occurring on cathode electrodes. However, to date, the reaction mechanism of alkaline HER is still under debate, which makes the design of catalysts largely a trial-and-error process. To address this issue, here we present strategies for the design of alkaline HER catalysts based on the current knowledge of the reaction mechanism by emphasizing the connection between the atomic-level materials engineering and reaction fundamentals. Particularly, we focus on the improvement of the inherent electronic structure of the materials to achieve desired interactions between the catalysts and reactive intermediates. By showing several successful examples of both theoretical and experimental design strategies, we aim to provide direct guidelines toward the design of catalysts for HER under alkaline conditions.
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Owing to its promising approach to tackling freshwater scarcity, solar-driven interfacial evaporation (SDIE) which confines the photothermal heat at evaporating surface has attracted ...tremendous research attention. Optimizing efforts on photothermal conversion and thermal management have greatly improved the SDIE performance. By taking advantage of the heat localization strategy, hybrid SDIE systems have been designed to enhance the solar energy utilization beyond water production. In this review, the development of SDIE and energy flow in hybrid system are discussed. The advanced conceptual designs of different hybrid applications such as electricity generation, fuel production, salt collection, photodegradation and sterilization are comprehensively summarized. Moreover, the current challenges and future perspectives of the hybrid systems are emphasized. This article aims to provide a systematic review on the recent progresses in hybrid SDIE systems to inspire both fundamental and applied research in capitalizing the undervalued auxiliary energy sources for future integrated water, energy and environmental systems.
Owing to an error in properly normalizing the reconstruction phase data into atomic displacements, the strain values that we used to calculate the root mean squared local strain, εrms, and to ...calculate the fraction of the crystals more strain than 1%, f, quoted in the original paper, are roughly one order of magnitude too large. This error was only discovered recently whilst performing further analysis.
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Carbon-based materials have multiple advantages including abundant sources, tunable molecular structures, high electronic conductivity, and environmental compatibility. Rapidly ...growing research interests are focused on carbon materials as electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), which are critical for sustainable energy technologies including fuel cells, metal-air batteries, and water electrolyzers. A number of papers in this area have been published. However, there is no systematic review yet covering all the general methods to boost carbon-based electrocatalysts for ORR/OER/HER, and reporting their most recent progress. To eliminate the gap, this contribution gives a timely and comprehensive review of such a rapidly growing field of great significance. This review starts with a brief introduction regarding the fundamentals of carbon-based ORR/OER/HER electrocatalysts and proceeds to summarize various synthesis methods of state-of-the-art carbon materials. Subsequently, the most popular strategies to optimize electrocatalytic properties of carbons are thoroughly reviewed. In addition to metal-free carbons, advances regarding hybridized and self-supported carbon electrocatalysts are discussed. This comprehensive review not only conveys the most recent research progress, but also provides essential ideas and methods that guide the design of high-performance carbon-based electrocatalysts, contributing to their large-scale adoption in sustainable energy applications.
Oxidation of graphite components could influence their designed life in a high-temperature nuclear reactor. The oxidized regions could potentially lower the allowed stress capacity. The American ...Society of Mechanical Engineers rules for the design and construction of graphite-moderated reactors recommend that subsurface regions that might become excessively damaged by oxidation during reactor operation be identified and excluded from geometry and stress calculations. Identification of oxidation-affected regions is possible, in principle, through complex modeling exercises of reactor behavior during hypothetical accident scenarios coupled with graphite oxidation models, but this procedure may not have the precision needed for informed decisions. Here, this paper proposes an alternate method, based on interpretation of a series of well-designed oxidation experiments, which could augment the designer's tools. The procedure is illustrated by data on oxidation by air of several graphite grades (NBG-18, PCEA, IG-110, R4-650) that are corroborated with independent literature information, when available. The Wichner model for graphite oxidation used for this analysis provides conservative results that could be quickly implemented in the design process.
Here, we use 79Br nuclear quadrupole resonance (NQR) to demonstrate that ultraslow lattice dynamics set in below the temperature scale set by the Cu-Cu superexchange interaction J (≃160 K) in the ...kagome lattice Heisenberg antiferromagnet Zn-barlowite. The lattice completely freezes below 50 K, and 79Br NQR line shapes become twice broader due to increased lattice distortions. Moreover, the frozen lattice exhibits an oscillatory component in the transverse spin echo decay, a typical signature of pairing of nuclear spins by indirect nuclear spin-spin interaction. This indicates that some Br sites form structural dimers via a pair of kagome Cu sites prior to the gradual emergence of spin singlets below ~30 K. Our findings underscore the significant roles played by subtle structural distortions in determining the nature of the disordered magnetic ground state of the kagome lattice.
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With the ever-growing development of multifunctional and miniature electronics, the exploring of high-power microwatt-milliwatt self-charging technology is highly essential. Flexible ...thermoelectric materials and devices, utilizing small temperature difference to generate electricity, exhibit great potentials to provide the continuous power supply for wearable and implantable electronics. In this review, we summarize the recent progress of flexible thermoelectric materials, including conducting polymers, organic/inorganic hybrid composites, and fully inorganic materials. The strategies and approaches for enhancing the thermoelectric properties of different flexible materials are detailed overviewed. Besides, we highlight the advanced strategies for the design of mechanical robust flexible thermoelectric devices. In the end, we point out the challenges and outlook for the future development of flexible thermoelectric materials and devices.
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