Magnetic skyrmions are swirling magnetic textures with novel characteristics suitable for future spintronic and topological applications. Recent studies confirmed the room-temperature stabilization of skyrmions in ultrathin ferromagnets. However, such ferromagnetic skyrmions show an undesirable topological effect, the skyrmion Hall effect, which leads to their current-driven motion towards device edges, where skyrmions could easily be annihilated by topographic defects. Recent theoretical studies have predicted enhanced current-driven behavior for antiferromagnetically exchange-coupled skyrmions. Here we present the stabilization of these skyrmions and their current-driven dynamics in ferrimagnetic GdFeCo films. By utilizing element-specific X-ray imaging, we find that the skyrmions in the Gd and FeCo sublayers are antiferromagnetically exchange-coupled. We further confirm that ferrimagnetic skyrmions can move at a velocity of ~50 m s−1 with reduced skyrmion Hall angle, |θSkHE| ~ 20°. Our findings open the door to ferrimagnetic and antiferromagnetic skyrmionics while providing key experimental evidences of recent theoretical studies.

Spin orbit torque (SOT) provides an efficient way to significantly reduce the current required for switching nanomagnets. However, SOT generated by an in-plane current cannot deterministically switch a perpendicularly polarized magnet due to symmetry reasons. On the other hand, perpendicularly polarized magnets are preferred over inplane magnets for high-density data storage applications due to their significantly larger thermal stability in ultrascaled dimensions. Here, we show that it is possible to switch a perpendicularly polarized magnet by SOT without needing an external magnetic field. This is accomplished by engineering an anisotropy in the magnets such that the magnetic easy axis slightly tilts away from the direction, normal to the film plane. Such a tilted anisotropy breaks the symmetry of the problem and makes it possible to switch the magnet deterministically. Using a simple Ta/CoFeB/MgO/Ta heterostructure, we demonstrate reversible switching of the magnetization by reversing the polarity of the applied current. This demonstration presents a previously unidentified approach for controlling nanomagnets with SOT.spin orbit torque | perpendicular anisotropy | nanomagnets S pin orbit coupling (SOC) and/or broken inversion symmetry in vertical heterostructures can generate accumulation of spins when a charge current is flowing through them. In doing so, it can exert a torque on an adjacent magnet (1-8). Indeed, high Z metals (Ta, Pt, W, etc.) with strong SOC have been used to inject spin currents into adjacent ferromagnetic layers and thereby to induce magnetic switching, oscillation, domain wall movement, etc. (1)(2)(3)(4)(5)(7)(8)(9). In a typical heterostructure such as Ta/CoFeB/MgO (from the bottom), an in-plane current flowing in the x direction (electrons flowing in the -x direction) generatesσ =ŷ polarized spins that accumulate at the Ta/CoFeB interface. Therefore, if the ferromagnet (CoFeB) is polarized in-plane, the spin accumulation can rotate it to the +y direction by a Slonczewski-like torqueτ sl = τ 0 sl

Single-crystal perovskite ferroelectric material is integrated at room temperature on a flexible substrate by the layer transfer technique. Two terminal memory devices fabricated with these materials exhibit faster switching speed, lower operating voltage, and superior endurance than other existing flexible counterparts. The research provides an avenue toward combining the rich functionality of charge and spin states, offered by the general class of complex oxides, onto a flexible platform.

Spin-polarized electrons can move a ferromagnetic domain wall through the transfer of spin angular momentum when current flows in a magnetic nanowire. Such current induced control of a domain wall is of significant interest due to its potential application for low power ultra high-density data storage. In previous reports, it has been observed that the motion of the domain wall always happens parallel to the current flow – either in the same or opposite direction depending on the specific nature of the interaction. In contrast, here we demonstrate deterministic control of a ferromagnetic domain wall orthogonal to current flow by exploiting the spin orbit torque in a perpendicularly polarized Ta/CoFeB/MgO heterostructure in presence of an in-plane magnetic field. Reversing the polarity of either the current flow or the in-plane field is found to reverse the direction of the domain wall motion. Notably, such orthogonal motion with respect to current flow is not possible from traditional spin transfer torque driven domain wall propagation even in presence of an external magnetic field. Therefore the domain wall motion happens purely due to spin orbit torque. These results represent a completely new degree of freedom in current induced control of a ferromagnetic domain wall.

The orbital Hall effect describes the generation of the orbital current flowing in a perpendicular direction to an external electric field, analogous to the spin Hall effect. As the orbital current carries the angular momentum as the spin current does, injection of the orbital current into a ferromagnet can result in torque on the magnetization, which provides a way to detect the orbital Hall effect. With this motivation, we examine the current-induced spin-orbit torques in various ferromagnet/heavy metal bilayers by theory and experiment. Analysis of the magnetic torque reveals the presence of the contribution from the orbital Hall effect in the heavy metal, which competes with the contribution from the spin Hall effect. In particular, we find that the net torque in Ni/Ta bilayers is opposite in sign to the spin Hall theory prediction but instead consistent with the orbital Hall theory, which unambiguously confirms the orbital torque generated by the orbital Hall effect. Our finding opens a possibility of utilizing the orbital current for spintronic device applications, and it will invigorate researches on spin-orbit-coupled phenomena based on orbital engineering.

Deep-ultraviolet (DUV) photodetectors based on wide-band-gap semiconductors have attracted significant interest across a wide range of applications in the industrial, biological, environmental, and military fields due to their solar-blind nature. As one of the most promising wide-band-gap materials, β-Ga2O3 provides great application potential over detection wavelengths ranging from 230 to 280 nm owing to its superior optoelectronic performance, stability, and compatibility with conventional fabrication techniques. Although various innovative approaches and device configurations have been applied to achieve highly performing β-Ga2O3 DUV photodetectors, the highest demonstrated responsivity of the β-Ga2O3 photodetectors has only been around 105 A/W. Here, we demonstrate a β-Ga2O3 phototransistor with an ultrahigh responsivity of 2.4 × 107 A/W and a specific detectivity of 1.7 × 1015 Jones, achieved by engineering a photogating effect. A β-Ga2O3/MgO heterostructure with an Al2O3 encapsulation layer is employed not only to reduce photogenerated electron/hole recombination but also to suppress the photoconducting effects at the back-channel surface of the β-Ga2O3 phototransistor via a defect-assisted charge transfer mechanism. The measured photoresponsivity is almost 2 orders of magnitude higher than the highest previously reported value in a β-Ga2O3-based photodetector, to the best of our knowledge. We believe that the demonstrated β-Ga2O3/MgO heterostructure configuration, combined with its facile fabrication method, will pave the way for the development of ultrasensitive DUV photodetectors utilizing oxide-based wide-band-gap materials.

The spin Hall effect describes an electric-field-induced generation of spin currents through spin-orbit coupling. Since the spin-orbit coupling alone cannot generate the angular momentum, there must be a more fundamental process of the spin Hall effect. Theories suggested that an electric-field-induced generation of orbital currents, called orbital Hall effect, is the fundamental process, and spin currents are subsequently converted from orbital currents. Despite its fundamental importance, the orbital Hall effect has not been confirmed experimentally. Motivated by a recent theoretical proposal of torque generation by orbital angular momentum injection, we examine the current-induced torque experimentally in various ferromagnet/heavy metal bilayers. We find that the net torque in Ni/Ta bilayers is opposite in sign to the spin Hall theory prediction but instead consistent with the orbital Hall theory, which confirms the orbital torque generated by the orbital Hall effect. It will invigorate researches on spin-orbit-coupled phenomena based on orbital engineering.

We report on the effect of Al 2 O 3 surface passivation on electrical properties of beta-gallium oxide (β-Ga 2 O 3) nanomembrane field-effect transistor (FET). The fabricated bottom-gate β-Ga 2 O 3 (100) FET exhibits enhanced channel conductance and reduced hysteresis after the conformal atomic layer deposited Al 2 O 3 passivation investigated by high-resolution transmission electron microscope (HR-TEM) analysis. Moreover, abnormal positive threshold voltage (V TH) shifts under negative bias stress are turned into negative V TH shifts, and off-state breakdown characteristics is improved as well. A modeling work using physics-based TCAD shows reduced surface depletion effect after the surface passivation. The results demonstrate that high-quality ALD-Al 2 O 3 surface passivation is an effective method to improve electrical properties of the bottom-gate β-Ga 2 O 3 FET and its device applications. INDEX TERMS β-Ga 2 O 3 , passivation, surface depletion.