which information is encoded by magnetic skyrmions in a magnetic wire structure. Skyrmion racetrack memory has been considered as an appealing alternative to next-generation memory technology because of its small skyrmion size, highspeed operation, and stability. [8][9][10] The minimum size of skyrmion can be smaller than that of the magnetic domain wall, [11] where the minimum size determines the maximized device density. In addition, based on additional topological stability, the critical depinning current density in the skyrmion racetrack memory device is four orders of magnitude lower than that in the domain-wall racetrack memory. Skyrmion racetrack memory requires the sequential operation of electrical generation, deletion, and shifting of individual skyrmions in a single racetrack device. [12] Hence, the realization of skyrmion racetrack memory has been considered to be a challenging issue, and the feasibilities of the three main operations of generation/ deletion/shift have typically been demonstrated individually. Specifically, since the experimental observations of magnetic skyrmions at room temperature, [13,14] various approaches have been proposed for skyrmion generation using magnetic fields, [13,15,16] current-induced spin torque, [14,[17][18][19][20] voltagecontrolled magnetic anisotropy, [21] and thermal energy. [22,23] The deletion and shift of skyrmions have been successively achieved by current-induced spin-orbit torque (SOT). [13,[16][17][18][19][20] In the manipulation of skyrmions, the inevitable skyrmion Hall effect, which must be removed for skyrmion racetrack application, has also been experimentally observed, [24,25] but can be suppressed using ferrimagnetic or synthetic antiferromagnetic systems. [26] At this stage, the remaining experimental challenge toward achieving skyrmion racetrack memory is the implementation of all these three operations within a single device. Büttner et al. [17] reported the two operations of generating and shifting skyrmion in one device using a tailored pinning site, whereas Woo et al. [18] achieved the electrical generation and deletion of a single skyrmion in one device using device-compatible geometry. In addition, Yu et al. [27] realized a skyrmion shift device using writing and shifting skyrmions in one device. However, whether all three operations of generation/deletion/shift can be realized on a single device has not been experimentally proven. Here, we introduce a practical method for generating and deleting isolated skyrmions via vertical current injection.The magnetic skyrmion is a topologically protected spin texture that has attracted much attention as a promising information carrier because of its distinct features of suitability for high-density storage, low power consumption, and stability. One of the skyrmion devices proposed so far is the skyrmion racetrack memory, which is the skyrmion version of the domain-wall racetrack memory. For application in devices, skyrmion racetrack memory requires electrical generation, deletion, and displacement ...

Efficient current‐induced switching of perpendicular magnetization is an essential task in spintronics for realizing high‐performance information processing and for storage device application. However, the spin‐orbit torque (SOT) by injection of in‐plane polarized spins cannot deterministically switch the magnetization of ferromagnetic thin films with perpendicular magnetic anisotropy (PMA) without an additionally applied in‐plane external magnetic field to break the symmetry of the PMA. Considering the difficulties of applying the magnetic field to the localized area only within a device structure, it is essential to contrive a facile field‐free SOT switching mechanism. Here, deterministic field‐free SOT switching of perpendicular magnetization is achieved in amorphous and ferrimagnetic Gd/Co multilayers accompanied by a tilted magnetic anisotropy axis. This tilted anisotropy originates from the combined contributions of many internal anisotropies in different orientations from the multilayers and is shown to be controllable. It is expected that the introduction of controlled tilted anisotropy into Gd/Co multilayers over the entire film surface in the present study can be extended to the development of wafer‐scale technologies for the spintronics memory and logic devices.

Magnetic domain wall (DW) motion in perpendicularly magnetized materials is drawing increased attention due to the prospect of new type of information storage devices, such as racetrack memory. To augment the functionalities of DW motion-based devices, it is essential to improve controllability over the DW motion. Other than electric current, which is known to induce unidirectional shifting of a train of DWs, an application of in-plane magnetic field also enables the control of DW dynamics by rotating the DW magnetization and consequently modulating the inherited chiral DW structure. Applying an external bias field, however, is not a viable approach for the miniaturization of the devices as the external field acts globally. Here, the programmable exchange-coupled DW motion in the antiferromagnet (AFM)/ferromagnet (FM) system is demonstrated, where the role of an external in-plane field is replaced by the exchange bias field from AFM layer, enabling the external field-free modulations of DW motions. Interestingly, the direction of the exchange bias field can also be reconfigured by simply injecting spin currents through the device, enabling electrical and programmable operations of the device. Furthermore, the result inspires a prototype DW motion-based device based on the AFM/FM heterostructure, that could be easily integrated in logic devices.

recognized that many different mechanisms are implementable, hence the modulation of carrier density, [1][2][3][4] piezoelectric strain effect, [5][6][7][8][9] exchange coupling, [10][11][12][13] orbital reconstruction, [14][15][16][17] and electrochemical effect [18][19][20] in various magnetoelectric coupling systems, consisting of an ferromagnet (FM), antiferromagnet (AFM), as well as ferroelectric (FE) materials in the thin film structures have been actively investigated. It is also noted that the relevant magnetic properties manipulated by VCMA include magnetization, magnetoresistance (MR), magnetic anisotropy (MA), coercivity (H C ), exchange bias field (H E ), and curie temperature (T C ), and the impact of VCMA technology in the application of magnetic material can be broadly extended to many areas. In the present article, we demonstrate that a transformation of magnetic anisotropy can be achieved at room temperature by electro-chemical effect at the interface between Co layer and Gd layer based on voltage-driven O 2− ion migrations within the amorphous Gd-O layer in Pt/Co/Gd/ GdO x /Pt multilayers structure. As the ion migration can be bidirectional depending on the polarity of applied voltage, magnetic anisotropy of the Co film could be reversibly transformed between perpendicular magnetic anisotropy (PMA) and inplane magnetic anisotropy (IMA). Unlike the recently reported VCMA results realized by the ionic migration mechanism accompanied with fully oxidation of FM metal layer, [18,19,21] present work here reports a large modulation in MA (≈4500 fJ/Vm) of the FM layer at room temperature without fully oxidizing the atoms in FM layer, thereby there is no need to sacrifice the magnetization. Change of MA is mainly from an induced PMA in the transition metal/oxide interface with the interfacial hybridization of transition metal and oxygen. [22][23][24] In order to further explore the MA control, domain morphology in FM was also examined. Many recent studies reported that skyrmions can be set in PMA films with stripe domain morphology by appropriately adjusting their MA and the domain widths via applications of external magnetic field [25,26] combined with thermal assistances. [27,28] Recent attentions to skyrmions are not only for a fundamental understanding of their topological With the prospect of energy-efficient spintronics by voltage-controlled magnetic anisotropy (VCMA), various mechanisms are investigated involving electron orbital state modulations for enhanced spin-orbit interactions, couplings with piezoelectric strain, and electrochemical effect at the interface within diverse magnetoelectric coupled material systems. In the present work, chemistry and spatial distributions of atoms are fine-tuned at the interface between ferromagnetic Co and partially oxidized Gd layers via voltage-controlled ion migrations, achieving highly sensitive and stable VCMA operations. With combined actions of chemical diffusion and electrical driving of oxygen through amorphous Gd layer, asymmetric electrical adjustm...

Field‐Free Switching In article number 2112561, Jung‐Il Hong, Chanyong Hwang, and co‐workers demonstrate field‐free spin‐orbit torque switching of perpendicular magnetization in amorphous and ferrimagnetic Gd/Co multilayers accompanied by a tilted magnetic anisotropy axis. This tilted anisotropy could facilitate the development of magnetic memory and logic devices without the need for external application of a global magnetic field or manufacturing complex magnetic structures to induce symmetry breaking.