No abstract

Low-dimensional spinel ferrites have recently attracted increasing attention because their tunable magnetic properties make them attractive candidates as spin-filtering tunnel barriers in spintronic devices and as magnetic components in artificial multiferroic heterostructures. Although we know that the distribution of cations (Fe and Co) in a spinel structure governs its magnetic properties, their distribution in the so-called ideal inverse spinel structure of a ferrite, CoFeO, has not yet been imaged with sub-ångstrom resolution. In this work, we fill this gap in evidence by reporting a direct observation of the distribution of cations in an ideal inverse spinel structure of CoFeO nanofibres using aberration-corrected transmission electron microscopy (TEM). The ordering of Co and Fe at the octahedral sites imaged along either [001], [011] or [-112] orientation was identified as 1 : 1, in accordance with the ideal inverse spinel structure. The saturation magnetisation calculated based on the crystal structure as determined from the TEM image is in good agreement with that measured experimentally on the spinel CoFeO nanofibres, further confirming results from TEM.

Polymers, as widely used non-viral gene carriers, suffer from high cytotoxicity and relatively low transfection efficiency. Such crucial drawbacks of polymers could be solved by incorporating short and bioactive peptides. The resulting synthetic polymer-peptide conjugates can not only maintain their own special characteristics, but also gain novel characteristics far beyond those of their parent polymer and peptide components to overcome barriers to gene delivery. There are various chemoselective reactions applied in the synthesis of polymer-peptide conjugates, such as Heck, Sonogashira and Suzuki coupling, Diels-Alder cycloaddition, click chemistry, Staudinger ligation, reductive alkylation and oxime/hydrazone chemistry. Among them, thiol-ene click reactions, including thiol-ene radical and thiol Michael addition reactions, are common methods for preparing peptide-polymer conjugates. In this review, we focus on thiol Michael addition reactions, elaborate on their mechanisms and highlight their applications in the synthesis of polymer-peptide conjugates for gene delivery.

Recently, magnetic skyrmion has attracted much attention due to its potential application in racetrack memory and other nanodevices. In bulk chiral magnets with non-centrosymmetric crystal structures, skyrmion lattice phase has been extensively observed. However, in film or multilayers with interfacial Dzyaloshinskii–Moriya interaction, individual skyrmion is often observed. Here, we report a short-ordered skyrmion lattice observed in [Ta­(5.0 nm)/CoFeB­(1.5 nm)/MgO­(1.0 nm)]15 multilayer in a remnant state. The structure, stabilization, and reversal of these skyrmions are discussed. Applying a slightly tilted in-plane magnetic field caused reversal of the skyrmion lattice. This reversal came from disappearance of skyrmions and nucleation of new skyrmions in the interstitial regions of the lattice. Also, we investigated how the skyrmion lattice depended on the CoFeB thickness. Our findings provide a pathway to stabilize and reverse the skyrmions in multilayers films.

Discovering the effect of magnetic anisotropy on the magnetization configurations of magnetic nanomaterials is essential and significant for not only enriching the fundamental knowledge of magnetics but also facilitating the designs of desired magnetic nanostructures for diverse technological applications, such as data storage devices, spintronic devices, and magnetic nanosensors. Herein, we present a direct observation of magnetocrystalline anisotropy tuning magnetization configurations in uniaxial magnetic nanomaterials with hexagonal structure by means of three modeled samples. The magnetic configuration in polycrystalline BaFeO nanoslice is a curling structure, revealing that the effect of magnetocrystalline anisotropy in uniaxial magnetic nanomaterials can be broken by forming an amorphous structure or polycrystalline structure with tiny grains. Both single crystalline BaFeO nanoslice and individual particles of single-particle-chain BaFeO nanowire appear in a single domain state, revealing a dominant role of magnetocrystalline anisotropy in the magnetization configuration of uniaxial magnetic nanomaterials. These observations are further verified by micromagnetic computational simulations.