The recent discovery of 2D magnetic order in van der Waals materials has stimulated a renaissance in the field of atomically thin magnets. This has led to promising demonstrations of spintronic ...functionality such as tunneling magnetoresistance. The frantic pace of this emerging research, however, has also led to some confusion surrounding the underlying phenomena of phase transitions in 2D magnets. In fact, there is a rich history of experimental precedents beginning in the 1960s with quasi‐2D bulk magnets and progressing to the 1980s using atomically thin sheets of elemental metals. This review provides a holistic discussion of the current state of knowledge on the three distinct families of low‐dimensional magnets: quasi‐2D, ultrathin films, and van der Waals crystals. It highlights the unique opportunities presented by the latest implementation in van der Waals materials. By revisiting the fundamental insights from the field of low‐dimensional magnetism, this review highlights factors that can be used to enhance material performance. For example, the limits imposed on the critical temperature by the Mermin–Wagner theorem can be escaped in three separate ways: magnetocrystalline anisotropy, long‐range interactions, and shape anisotropy. Several recent experimental reports of atomically thin magnets with Curie temperatures above room temperature are highlighted.
This review discusses 2D magnets with applications for low‐energy spintronics with an emphasis on experimental phenomena. Historical examples are discussed beginning in the 1960s. Recent progress using cleavable van der Waals materials in the period from 2016–2018 is highlighted. The theoretical mechanisms for improved magnetic performance are introduced and discussed against the background of experimental evidence.
The search for active catalysts that efficiently oxidize methane under ambient conditions remains a challenging task for both C1 utilization and atmospheric cleansing. Here, we show that when the ...particle size of zinc oxide is reduced down to the nanoscale, it exhibits high activity for methane oxidation under simulated sunlight illumination, and nano silver decoration further enhances the photo-activity via the surface plasmon resonance. The high quantum yield of 8% at wavelengths <400 nm and over 0.1% at wavelengths ∼470 nm achieved on the silver decorated zinc oxide nanostructures shows great promise for atmospheric methane oxidation. Moreover, the nano-particulate composites can efficiently photo-oxidize other small molecular hydrocarbons such as ethane, propane and ethylene, and in particular, can dehydrogenize methane to generate ethane, ethylene and so on. On the basis of the experimental results, a two-step photocatalytic reaction process is suggested to account for the methane photo-oxidation.
The development of low-cost and long-lasting all-climate cathode materials for the sodium ion battery has been one of the key issues for the success of large-scale energy storage. One option is the ...utilization of earth-abundant elements such as iron. Here, we synthesize a NASICON-type tuneable Na
Fe
(PO
)
(P
O
)/C nanocomposite which shows both excellent rate performance and outstanding cycling stability over more than 4400 cycles. Its air stability and all-climate properties are investigated, and its potential as the sodium host in full cells has been studied. A remarkably low volume change of 4.0% is observed. Its high sodium diffusion coefficient has been measured and analysed via first-principles calculations, and its three-dimensional sodium ion diffusion pathways are identified. Our results indicate that this low-cost and environmentally friendly Na
Fe
(PO
)
(P
O
)/C nanocomposite could be a competitive candidate material for sodium ion batteries.
Manganese‐based Prussian Blue, Na2−δMnFe(CN)6 (MnPB), is a good candidate for sodium‐ion battery cathode materials due to its high capacity. However, it suffers from severe capacity decay during ...battery cycling due to the destabilizing Jahn–Teller distortions it undergoes as Mn2+ is oxidized to Mn3+. Herein, the structure is stabilized by a thin epitaxial surface layer of nickel‐based Prussian Blue (Na2−δNiFe(CN)6). The one‐pot synthesis relies on a chelating agent with an unequal affinity for Mn2+ and Ni2+ ions, which prevents Ni2+ from reacting until the Mn2+ is consumed. This is a new and simpler synthesis of core–shell materials, which usually needs several steps. The material has an electrochemical capacity of 93 mA h g−1, of which it retains 96 % after 500 charge–discharge cycles (vs. 37 % for MnPB). Its rate capability is also remarkable: at 4 A g−1 (ca. 55 C) it can reversibly store 70 mA h g−1, which is also reflected in its diffusion coefficient of ca. 10−8 cm2 s−1. The epitaxial outer layer appears to exert an anisotropic strain on the inner layer, preventing the Jahn–Teller distortions it normally undergoes during de‐sodiation.
A Mn‐based Prussian Blue analogue prone to destabilizing Jahn–Teller distortions upon oxidation is coated with an epitaxial layer of Ni‐based Prussian Blue. This outer layer exerts an anisotropic strain on the lattice of the inner layer, largely preventing structural degradation during Na+ extraction and re‐insertion. As a sodium‐ion battery cathode, the material combines the high capacity and high stability of its two components.
Whereas the application of optically or magnetically heated nanoparticles to destroy tumours is now well established, the extension of this concept to target pathogens has barely begun. Here we ...examine the challenge of targeting pathogens by this means and, in particular, explore the issues of power density and heat transfer. Depending on the rate of heating, either hyperthermia or thermoablation may occur. This division of the field is fundamental and implies very different sources of excitation and heat transfer for the two modes, and different strategies for their clinical application. Heating by isolated nanoparticles and by agglomerates of nanoparticles is compared: hyperthermia is much more readily achieved with agglomerates and for large target volumes, a factor which favours magnetic excitation and moderate power densities. In contrast, destruction of planktonic pathogens is best achieved by localised thermoablation and very high power density, a scenario that is best delivered by pulsed optical excitation.
•Alloy formation in ultrathin Co/Pd multilayers.•Structural CoPd alloy thin film with magnetic properties of Co/Pd multilayers.•Hydrogen induced FMR shift in Co/Pd multilayers.•A dependence of this ...shift on the nominal Pd thickness.•A dependence of the magnetic damping on nominal Pd thickness in Co/Pd multilayers.
It is known that large perpendicular magnetic anisotropy is found at interfaces of cobalt (Co) with palladium (Pd). We investigated Pd/Co/Pd30/Pd multilayer thin films with very thin Co and Pd layers with ferromagnetic resonance (FMR) spectroscopy in air and in hydrogen gas. A number of samples characterised by different Pd thicknesses were studied. A ferromagnetic resonance (FMR) peak shift similar to Co/Pd bilayer thin films was observed in the presence of hydrogen gas in the sample environment for all samples. The FMR peak shift is larger for samples with thicker Pd layers. Additionally, we found a dependence of the linewidth on the Pd layer thickness and explain this with the presence of spin pumping.
Herein, we introduce a 4.0 V class high‐voltage cathode material with a newly recognized sodium superionic conductor (NASICON)‐type structure with cubic symmetry (space group P213), Na3V(PO3)3N. We ...synthesize an N‐doped graphene oxide‐wrapped Na3V(PO3)3N composite with a uniform carbon coating layer, which shows excellent rate performance and outstanding cycling stability. Its air/water stability and all‐climate performance were carefully investigated. A near‐zero volume change (ca. 0.40 %) was observed for the first time based on in situ synchrotron X‐ray diffraction, and the in situ X‐ray absorption spectra revealed the V3.2+/V4.2+ redox reaction with high reversibility. Its 3D sodium diffusion pathways were demonstrated with distinctive low energy barriers. Our results indicate that this high‐voltage NASICON‐type Na3V(PO3)3N composite is a competitive cathode material for sodium‐ion batteries and will receive more attention and studies in the future.
A new NASICON‐type high‐voltage cathode material of Na3V(PO3)3N was synthesized and its electrochemical performance was improved by carbon matrix decoration. An in‐depth investigation of the material was performed through in situ XAS and XRD, and its 3D sodium pathways were clearly identified through DFT calculations.
High-quality NdCrSb3 single crystals are grown using a Sn-flux method, for electronic transport and magnetic structure study. Ferromagnetic ordering of the Nd3+ and Cr3+ magnetic sublattices are ...observed at different temperatures and along different crystallographic axes. Due to the Dzyaloshinskii–Moriya interaction between the two magnetic sublattices, the Cr moments rotate from the b axis to the a axis upon cooling, resulting in a spin reorientation (SR) transition. The SR transition is reflected by the temperature-dependent magnetization curves, e.g., the Cr moments rotate from the b axis to the a axis with cooling from 20 to 9 K, leading to a decrease in the b-axis magnetization f and an increase in the a-axis magnetization. Our elastic neutron scattering along the a axis shows decreasing intensity of magnetic (300) peak upon cooling from 20 K, supporting the SR transition. Although the magnetization of two magnetic sublattices favours different crystallographic axes and shows significant anisotropy in magnetic and transport behaviours, their moments are all aligned to the field direction at sufficiently large fields (30 T). Moreover, the magnetic structure within the SR transition region is relatively fragile, which results in negative magnetoresistance by applying magnetic fields along either a or b axis. The metallic NdCrSb3 single crystal with two ferromagnetic sublattices is an ideal system to study the magnetic interactions, as well as their influences on the electronic transport properties.
A grand challenge in the field of magnetism is to find material systems that exhibit spin structures ranging from simple ferromag- nets to exquisite non-collinear states. In bulk three-dimensional ...（3D） materials, however, the magnetic exchange interactions are constrained by the crystal symmetry and quantum chemistry, mak- ing it challenging to adjust the intrinsic magnetic structure. A major advance for the custom-design of spin structures was the discovery that the exchange interaction can be fine-tuned in nanoscale thin film multilayers to produce either ferromagnetic （FM） or antiferro- magnetic （AF） interactions. This effect, known as interlayer exchange coupling （IEC）, is adjustable using a thin nonmagnetic spacer layer interleaved between two magnetic layers. The first indisputable experimental evidence of this magnetic coupling was demonstrated in the 1980＇s using metallic Fe/Cr and rare-earth based multilayers 1. The ability to engineer the exchange interac- tion introduced an unprecedented level of control to produce nanostructures known as synthetic antiferromagnets （Fig. 1）. Ulti- mately, this led to the discovery of novel transport and spintronic phenomena culminating in the 2007 Nobel Prize （https：//www.no- belprize.org/nobel_prizes/physics/laureates/2007）.
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