Dynamic Of Magnetic Skyrmion Using Micromagnetic Simulations

Magnetic skyrmions are topological spin texures,which possess great potential applications in next-generation spintronics,such as racetrack memory,microwave detector,logic gates and neuromorphological device.Controllable manipulation of skyrmion motion is fundamental to understanding the physics of skyrmions and their potential applications in spintronic devices.In this work,we investigated controllable manipulation of skyrmion in ferriomagnetic manterials and antiferriomagnetic materials using micromagnetic simulation.The main research contents of this paper are as follows:Firstly,we investigated skyrmion motion induced by the gradient of voltage-controlled magnetic anisotropy?VCMA?.Simulations show that the VCMA gradient can induce the skyrmion into a steady motion along the magnetic strip without reflection.The velocity of magnetic skyrmion lineally increases from 0.1 m/s to 23m/s with the VCMA gradient increasing from-1.0×10¹⁰ J/m⁴ to-8.0×10¹⁰ J/m⁴.The skyrmion velocity is inverse proportion to the damping factor.Furthermore,both the direction and velocity of skymion motion can be modulated by the VCMA gradient and in-plane filed.An analytical model based on the Thiele theory was derived,which was well in agreement with the simulation results.Secondly,the 2?skyrmion pinning by constrictions and protrusions in racetrack was investigated.The simulations demonstrated that energy barriers or energy wells are generated by constrictions and protrusions due to the demagnetizing and DMI.From the energy point of view,both types of constrictions and protrusions were found to act as pinning centers for 2?skyrmion.Spin waves were employed to induce 2?-skyrmion motion to study the dynamics of the 2?-skyrmion pinning.The simulations showed that the pinning/depinning of 2?-skyrmion exhibits dependence on the type and depth of constrictions and protrusions,as well as the frequency and amplitude of the oscillating magnetic field for exciting spin waves.Thirdly,the influence of the local magnetic field on the pinning/depinning behavior of 2?skyrmions was investigated.Firstly,we investigated the influence of AFM materials on the pinning/depinning of 2?skyrmion.The AFM nanowires can induce exchange bias field at the AFM/FM crossing areas,which can act as pinning sites.The strength of pinning depends on the exchange bias field.The interaction mechanism between the exchange bias and 2?skyrmion was studied from the energy point of view.Energy barriers or energy wells are generated at the AFM/FM crossing area due to the demagnetizing,DMI and exchange bias energy.Secondly,the effect of the local magnetic disk on the pinning/depinning behavior of 2?skyrmions was studied.Simulation results demonstrate that the magnetic disk can generate energy wells and then can serve as the pinning sites for 2?skyrmion.The strength of pinning depends on the diameter of the local magnetic disk.Finally,the electrical writing,driving and reading of AFM skyrmions were realized.Furthermore,duplication and deletion of skyrmions,logical OR and AND function were designed in AFM materials with a cusp or smooth Y-junction structures.The operational time is in dozens of picoseconds,enabling ultrafast information processing.Key factor for the successful operation is the relatively complex Y-junction structures,where domain walls propagate in a controlled manner,without significant risk of pinning,vanishing or unwanted depinning of existing domain walls as well as nucleation of new domain walls.The motion of AFM skyrmion chain in racetrack was also investigated.The AFM skyrmion chain velocity,independent of the skyrmions number of each skyrmion-chain,is in proportion to the current density.