Double-shelled Co/C/polyaniline (Co/C/PA) nanocomposites were prepared by combining the arc-discharge process and in situ chemical oxidative polymerization reaction. The effects of PA shells on the magnetic properties of Co/C/PA nanocomposites were studied, and the electromagnetic properties of Co/C/PA–paraffin composites were investigated in the 2–18 GHz frequency range. The reflection loss (RL) exceeding −10 dB is obtained in 9.9–16.4 GHz for an absorber thickness of 2.5 mm, which covers almost half of the X-band (8–12 GHz) and most of the Ku-band (12–18 GHz). Moreover, some strong absorption peaks exceeding −40 dB can be observed in the low-frequency range (3.5–5.5 GHz). These excellent absorbing performances show that the Co/C/PA nanocomposites have great potential for application in a microwave-absorption field for their strong absorption and broad bandwidth.

Interfacial moiré superlattices in van der Waals vertical assemblies effectively reconstruct the crystal symmetry, leading to opportunities for investigating exotic quantum states. Notably, a two-dimensional nanosheet has top and bottom open surfaces, allowing the specific case of doubly aligned super-moiré lattice to serve as a toy model for studying the tunable lattice symmetry and the complexity of related electronic structures. Here, we show that by doubly aligning a graphene monolayer to both top and bottom encapsulating hexagonal boron nitride (h-BN), multiple conductivity minima are observed away from the main Dirac point, which are sensitively tunable with respect to the small twist angles. Moreover, our experimental evidences together with theoretical calculations suggest correlated insulating states at integer fillings of −5, −6, −7 electrons per moiré unit cell, possibly due to inter-valley coherence. Our results provide a way to construct intriguing correlations in 2D electronic systems in the weak interaction regime.

In chalcogenide topological insulator materials, two types of magnetoresistance (MR) effects are widely discussed: a sharp MR dip around zero magnetic field, associated with the weak antilocalization (WAL) effect, and a linear MR (LMR) effect that generally persists to high fields and high temperatures. We have studied the MR of thin films of the topological insulator Bi₂Te₃ from the metallic to semiconducting transport regime. In the metallic samples, the WAL is difficult to identify owing to the low magnitude of the WAL compared to the samples’ conductivity. Furthermore, the sharp WAL dip in the MR is clearly present in samples with a higher resistivity. To correctly account for the low-field MR with the quantitative theory of the WAL according to the Hikami–Larkin–Nagaoka (HLN) model, we find that the classical (linear) MR effect should be taken into account in combination with the WAL quantum correction. Otherwise, the WAL fitting alone yields an unrealistically large coefficient α in the HLN analysis. This work clarifies the WAL and LMR as two distinct effects and offers an explanation for the overly large α in the WAL analysis of topological insulators in some studies.

ZnCoO:H nanocrystals are weak ferromagnetic at room temperature with a small coercivity and a small remanence, whereas ZnCoO nanocrystals are paramagnetic. The thermal irreversibility of zero-field cooling and field cooling magnetizations of ZnCoO:H nanocrystals corresponds to the existence of superparamagnetism due to the nanosize effect. X-ray photoelectron spectra show the incorporation of ${\mathrm{Co}}^{2+}$ ions inside the ZnO lattice without changing the wurtzite structure. Our data suggest that hydrogen can induce ferromagnetism in ZnCoO and that ferromagnetic ZnCoO:H crystals with small particle size can show the superparamagnetism.