Many factors can affect microwave absorption performance, including impedance matching, attenuation constant, electromagnetic (EM) loss capacity, multi-reflection and scattering and so on. In this work, corncob-derived carbon/Ni composites have been chosen to judge which factor has the greatest influence on the EM absorption behaviors, in which the surface area and pore size have been adjusted by the amount of chemical active additive. Closer impedance matching, larger attenuation constant and stronger EM loss capacity result in the good microwave absorbing behaviors of corncob-derived carbon/Ni composites when the mass ratio of KOH: corncob is 1.5. Minimal reflection loss values can reach −50.25 dB at 12 GHz and the effective bandwidth is 2.24 GHz and reflection loss values start be less than −10 dB at 1.2 mm. Through the analysis of morphology, microstructure, surface area and EM properties, it can be concluded that impedance matching is the most important for obtaining good microwave absorption performances, followed by EM loss ability and attenuation constant, and finally the multi-reflection and scattering by surface area.

A magnetic skyrmion could be endowed with various dynamic magnetic configurations and behaviors. By artificially generating a gradient magnetic field in a confined nanochannel, we have shown the magnetic dynamics of an isolated skyrmion, achieving the coexistence of moving and breathing modes. Such a phenomenon has been proven to be not only correlated to the gradient strength of a magnetic field, but also depends on the Dzyaloshinskii-Moriya interaction. By increasing the magnetic field gradient up to 0.1 mT nm −1 , the skyrmion can effectively overcome the skyrmion Hall effect, and meanwhile generate a breathing mode during the motion process under MFG=1.0 mT nm −1 and DMI=2.8 mJ m −3 . The present study could provide an alternative approach to regulate the skyrmion at micro/nanoscales by using a gradient magnetic field.

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Understanding the magnetic phase transition in zigzag-edged graphene nanoribbons has attracted considerable interest because of the unique properties generated from the quantum confinement and interference. However, it would be extremely difficult to experimentally integrate these nanoribbons with an ideal graphene in microelectronic devices because of their complexity, which could thus result in unexpected characteristics. By artificially generating the fluctuation field on single-layer graphene, we theoretically show how the fluctuation amplitude modifies the magnetic behaviors of the graphene system. It is proven that, by increasing fluctuation amplitude gradually, the magnetic correlated two edge state presents two typical oscillation behaviors between the antiferromagnetic and the ferromagnetic state depending on the nanoribbon width and doping concentration and then reaches the ground state of paramagnetism by further increasing the fluctuation amplitude. These findings not only uncover the influence of fluctuation on the intrinsic magnetic behaviors of nanoscale graphene ribbons, but also demonstrate effective control using external architecture that could be realized by artificial fabrication.

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