We report broadband microwave absorption spectroscopy of the layered antiferromagnet CrCl3. We observe a rich structure of resonances arising from quasi-two-dimensional antiferromagnetic dynamics. Due to the weak interlayer magnetic coupling in this material, we are able to observe both optical and acoustic branches of antiferromagnetic resonance in the GHz frequency range and a symmetry-protected crossing between them. By breaking rotational symmetry, we further show that strong magnon-magnon coupling with large tunable gaps can be induced between the two resonant modes.arXiv:1902.05669v2 [cond-mat.mtrl-sci]

Electrical control and detection of magnetic ordering inside antiferromagnets has attracted considerable interests, for the potential advantages in operating speed and device densities.In contrast to ferromagnets, where the current-induced torque on magnetic moments can be analyzed via comparison with magnetic field's influence, the quantitative investigation on the spin torque mechanism in antiferromagnets represents a greater challenge, due to the lack of a convenient, independent method for controlling Né el vectors. Here by utilizing an antiferromagnetic insulator with Dzyaloshinskii-Moriya interaction, α-Fe2O3, we show that the Né el vector can be easily controlled with the application of a moderate external magnetic field, which can be further used to examine the current-induced magnetic dynamics. We find that in this antiferromagnetic insulator, current-induced magnetoresistance change can be complicated by resistive switching that does not have a magnetic origin. By excluding nonmagnetic switching and comparing the current-induced and field-induced Né el vector tilting, we reveal the important role of magnetoelastic effect in current-induced dynamics of this antiferromagnet. The nature and magnitude of magnetoelastic effect is further determined and compared with possible spin orbit torque influences.

The commonly employed formamidinium (FA)-containing perovskite solar cells (PSCs) exhibit a severe phase instability problem, thereby limiting their commercial applications. Here, both phase stability and energy efficiency of FA-based PSCs were improved by treating the perovskite surface with pyrrolidinium hydroiodide (PyI) salts, resulting in a 1D perovskite structure (PyPbI3), stacked on the original 3D perovskite. By employing in situ XRD measurements, we revealed that the temperature-dependent phase transition activation barrier was enhanced after forming the 1D/3D structure, resulting in a prolonged transition time by 30–40-fold. From the first-principle calculations, we found the thermodynamic energy difference between two phases reduced from −0.16 to −0.04 eV after the stacking of 1D PyPbI3, offering additional lifetime improvement. Moreover, the champion 1D/3D bilayer PSC exhibits a boosted power conversion efficiency of 19.62%, versus 18.21% of the control. Such 1D/3D bilayer structure may be employed in PSCs to enhance their phase stability and photovoltaic performance.

The mechanism of the oxygen evolution reaction over NiFe-layered double hydroxides is investigated using first-principles DFT ? U calculations. We consider three possible reaction pathways for O 2 evolution. Our calculations show that O 2 evolution from the OH*-OH* species has high energy barrier and from OOH* species have a little high energy barrier. Finally, we discover that O 2 can easily release from OO* species. Graphical Abstract The mechanism of oxygen evolution reaction (OER) over NiFe-layered double hydroxides was investigated using DFT ? U method by First-principle. The present work considered two possible reaction pathways for O 2 evolution. Our calculation suggested that O 2 evolution from the OOH* species may be more favorable because of advantages in energy profile, oxygen adsorption, and overall energy barrier. In addition, density of states (DOS) and partial density of states (PDOSs) of NiFe-LDH and Ni(OH) 2 showed that NiFe-LDH had a more stronger capability for electron transportation and higher activity than Ni(OH) 2 . Additionally, it was found that Bader charge of Ni had a large fluctuation in the former elementary steps, while in the later that of Fe had. The research suggested that the transitional metal Fe/Ni-based hydrotalcite was a suitable material for OER, for not only they had great activity and stability, but also they were widely used and comparatively cheap.

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