Spin transfer nano-oscillators (STNOs) are nanoscale devices which are promising candidates for onchip microwave signal sources. For application purposes, they are expected to be nano-sized, to have broad working frequency, narrow spectral linewidth, high output power and low power consumption. In this paper, we demonstrate by micromagnetic simulation that magnetic skyrmions, topologically stable nanoscale magnetization configurations, can be excited into oscillation by a spin-polarized current. Thus, we propose a new kind of STNO using magnetic skyrmions. It is found that the working frequency of this oscillator can range from nearly 0 Hz to gigahertz. The linewidth can be smaller than 1 MHz. Furthermore, this device can work at a current density magnitude as small as 10 8 A m −2 , and it is also expected to improve the output power. Our studies may contribute to the development of skyrmion-based microwave generators. IntroductionSkyrmions are topologically protected objects with particle-like properties that play an important role in many different contexts, such as liquid crystals [1], quantum Hall magnets [2], Bose-Einstein condensates [3], etc. Recently, with the development of observation technology, particularly in the domain of neutron scattering [4], spin-polarized scanning tunneling microscopy (STM) [5], Lorentz force microscopy [6-8], and electron holography [9], skyrmions have been observed in bulk ferromagnetic crystals, thin films and nanowires. The spin texture of magnetic skyrmions is a stable configuration that, in most systems, results from a balance between the ferromagnetic exchange coupling, the Zeeman energy from the applied field and the chiral interaction, known as the Dzyaloshinskii-Moriya interaction (DMI) [10][11][12]. The DMI is induced because of the lack of, or breaking of, inversion symmetry in the magnetic structure, either due to the non-centrosymmetric crystal lattice or to the interfaces between different materials [8].Magnetic skyrmions were originally discovered in bulk ferromagnets lacking inversion symmetry, such as MnSi [13], FeGe [7,14], Fe 0.5 Co 0.5 Si [15] and other B20 transition metal compounds [16]. Then they were observed in thin films and nanowires of similar materials [9,17,18], and recently, in the multiferroic insulator Cu 2 OSeO 3 [19]. In addition, a more stable two-dimensional skyrmion crystal has been created artificially by nanopatterning [20] and a spontaneous skyrmion ground state has been created in Co/Ru/Co multilayer nanodisks without the DMI (the competition of the exchange energy, demagnetization energy and uniaxial anisotropy energy acts similar to the DMI) by a numerical approach [21]. Meanwhile, an effective method was reported to nucleate or annihilate isolated skyrmions experimentally by using STM at one monolayer of Fe grown in Ir(111) [22].It was recently realized that the magnetic skyrmions not only have mathematical beauty but can also be used as spintronic devices. Recent research has demonstrated that magnetic skyrmions have great potentia...

Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its property of topological protection. Our results present the understanding of antiferromagnetic skyrmion motion driven by the spin Hall effect and may also contribute to the development of antiferromagnetic skyrmion-based racetrack memories.

Controllable manipulations of magnetic skyrmions are essential for next-generation spintronic devices. Here, the duplication and merging of skyrmions, as well as logical AND and OR functions, are designed in antiferromagnetic (AFM) materials with a cusp or smooth Y-junction structures. The operational time are in the dozens of picoseconds, enabling ultrafast information processing. A key factor for the successful operation is the relatively complex Y-junction structures, where domain walls propagate through in a controlled manner, without significant risks of pinning, vanishing or unwanted depinning of existing domain walls, as well as the nucleation of new domain walls. The motions of a multi-bit, namely the motion of an AFM skyrmion-chain in racetrack, are also investigated. Those micromagnetic simulations may contribute to future AFM skyrmion-based spintronic devices, such as nanotrack memory, logic gates and other information processes.

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