Search

We demonstrate a tunable spin–orbit torque (SOT) switching in an antiferromagnetically coupled CoFeB/Ta/CoFeB trilayer through careful design of magnetic anisotropies, where the thicker bottom CoFeB layer has a relatively weak perpendicular magnetic anisotropy (PMA) and PMA of the upper CoFeB layer is robust. The unique anisotropy feature causes a strong sensitivity to the assistant field during SOT switching, resulting in a slanted magnetic moment and a highly tunable switching window defined by the difference in Hall resistance between two SOT switching states at zero current. By further reducing the PMA of bottom CoFeB, only the upper layer can be switched by SOT. Until now, there are three types of SOT switching in antiferromagnetically coupled ferromagnetic metal/nonmagnetic metal/ferromagnetic metal trilayers: simultaneous switching between two antiparallel states with strong PMA for both ferromagnetic layers, field-free switching where one layer has in-plane magnetization and the other has canted out-of-plane magnetization, and tunable switching reported in this work. Our findings enrich the physical phenomena in trilayer SOT and may have potential application in multilevel storage and neural computing.

The anomalies in the transverse resistivity are usually thought to be Topological Hall Effects (THEs), which have been considered as the trait of topologically nontrivial spin textures, such as the skyrmion phase. However, the origin of the THE-like features is still under debate. Here, we present the observation of THE-like features in synthetic antiferromagnetic [Pd/Co]/Ru/[Co/Pd] and synthetic ferromagnetic [Pd/Co]/NiO/[Co/Pd] structures. The Pd-rich alloys, which are formed due to the heterogeneous component and the gradual intermixing at the Co/Pd interface, result in a negative anomalous Hall effect coefficient, causing the peak and dip features in transport measurements. By changing the external magnetic field from out-of-plane to in-plane, the magnitude and width of the bump feature in THE curves can be modified, which is caused by the different anisotropy energy of the components in the heterogeneous ferromagnets. The present work broadens the perception of THE-like features and may add a different dimension to understand the magnetization reversal in magnetic multilayers.

In this Letter, we developed a sprayable superhydrophobic coating with micro-sized disorder indentations to survey the self-ejections of isolated slushes on it during the defrosting process. The microstructures, chemical composition, hydrophobic characteristics, and self-ejection phenomenon of melting slushes on grooved superhydrophobic surfaces are presented. The grooved superhydrophobic surface demonstrates that multiple self-ejections of isolated melting slush off the original locations with no ice bridges or great surface energy release. In addition, the self-ejection of multiple isolated slushes observed generates enough kinetic energy and removes the residual melting slushes in ways of sweeping off. It is also found that the irregular melting slush with a greater deformation energy and surface contact area demonstrates shorter jumping distances compared to that with a spherical shape and low surface contact area. The observed short-distance self-ejection results from the defects of micro-pores on the indentations, leading to great dissipation in vapor pressures and reduced impact from volume fluctuations. Both the volume fluctuation of slush and the evaporation of intermediate liquid generate the pressure gradient in the upward direction and contribute to the self-ejection behavior of isolated melting slush. The results demonstrate the necessity of fabricating grooved superhydrophobic surfaces without micro-pores and conceptual feasibility of employing volume fluctuation of slush for the self-ejection of isolated single melting slush in the case of slushes with no ice bridges, small surface energy, and low inner vapor pressures.

A perpendicularly magnetized synthetic antiferromagnetic structure is a promising alternative to a single ferromagnetic layer in spintronic applications because of its low net magnetization and high thermal stability. In general, the reversal sequences of the two ferromagnetic layers in the structure are fixed for a specific sample since they have different magnetic anisotropy. Here, we investigate the anomalous Hall effect of the [Pd/Co]/Ru/[Co/Pd] synthetic antiferromagnetic structure. By rotating the external field from out-of-plane to in-plane, three different types of anomalous Hall effect curves can be observed, which shows obvious magnetic field direction dependent magnetization reversal behavior. The mechanism can be explained with the help of the Stoner-Wohlfarth model calculation, and the result indicates that the competition among Zeeman, anisotropy, and exchange coupling energies in the system is sensitive to the magnetic field direction, which changes the switching sequences. Besides the fundamental significance, our finding provides a different dimension to manipulate the performance of spintronics.

The spin valve effect driven by the magnetic field in sandwich structures stands out as a seminal phenomenon in the emerging field of spintronics, but it has not been realized in low-power-dissipation devices operated via electrical means. Here, we investigate spin-orbit torque switching in a perpendicularly magnetized CoFeB/Mo/CoFeB sandwich, where the spin current generated in the Mo layer flows upward and downward to the ferromagnetically coupled CoFeB layers. When scanning the current, two CoFeB layers can be switched from one antiparallel state to a parallel state and then to the other antiparallel state, producing an unprecedentedly current-dependent spin valve effect. Such a spin valve effect is sensitive to the additional magnetic field direction due to the small spin torque efficiency and efficiency difference of the two CoFeB layers. The experimental observations are supported by the dynamics simulation based on the Landau-Lifshitz-Gilbert equation. Besides the fundamental interest, our finding would add a different dimension to energy efficient memory devices and sensors.

A newly synthesized layered material C2N was investigated based on many- body perturbation theory using GW plus Bethe-Salpeter equation approach. The electronic band gap was determined to be ranging from 3.75 to 1.89 eV from monolayer to bulk. Significant GW quasiparticle corrections, of more than 0.9 eV, to the Kohn-Sham band gaps from the local density approximation (LDA) calculations are found. Strong excitonic effects play a crucial role in optical properties. We found large binding energies of greater than 0.6 eV for bound excitons in few-layer C2N, while it is only 0.04 eV in bulk C2N. All the structures exhibit strong and broad optical absorption in the visible light region, which makes C2N a promising candidate for solar energy conversion, such as photocatalytic water splitting., Comment: 13 pages, 4 figures