Micromagnetic Study Of Skyrmions-based Racetrack Memory

Electrons have two properties: charge properties and spin properties.We have seen the wide application of charge properties,which has profoundly changed the social form of human beings and people's way of life.Spintronics looks at the spin properties of electrons,has achieved great success and has a good development prospect.As a rising star in spintronics,magnetic skyrmion is a topologically stable vortical spin structure.In 2006,Bogdanov predicted that there may be magnetic skyrmions in FeGe and MnSi.In 2009,German scientist Pfleiderer observed skyrmions for the first time in experiments.Magnetic skyrmions have some excellent properties: small size,topological stability,extremely low critical drive current,which brings possibility to applications,and the most promising one is to use skyrmions as information carriers.Compared with traditional methods,which utilizes domain walls as information carrier,skyrmions have better performance and are more suitable as information bits for racetrack storage.Traditional racetrack memory utilizes a nanowire as racetrack and magnetic domain walls as information carrier.Domain walls are driven by spinpolarized current when reading or writing bits.Driving current density of skyrmion is five to six orders smaller,which implies that skyrmion-based racetrack memory could be low power dissipation.Although skyrmion-based racetrack memory is obviously advanced,there still exists a bit of problems before bringing it to practical application,waiting for researchers to suggest solutions.In this article,we first give the relevant background knowledge of spintronics,then introduce the magnetic skyrmions,and describe the racetrack storage based on skyrmions and some other applications of skyrmions.Next,we introduce the difficulty of skyrmion application in racetrack storage-the skyrmion Hall effect.When skyrmion moves along the racetrack,it gets horizontal movement caused by the Magnus force,which is known as the skyrmion Hall effect(Sk HE).As a result,skyrmion might annihilate when it reaches one edge of the racetrack,and it leads to the loss of information.At the same time,we also mentioned existing solutions.Aiming at the Skyrmion Hall effect,we proposed a new solution to it by creating a track with a damping gradient.In the racetrack we designed,the damping coefficient of the racetrack is not uniformly distributed,but with a gradient that changes from one side of the racetrack to the other.Skyrmions tend to follow the exact track we establish and remain stable during transmission and will not be destroyed by hitting the edge of the track.In order to verify the feasibility of this method,we adopted the method of micromagnetic simulation for verification,discussed the influence of various factors on the results,and compared our work with the existing solutions.Through the above analysis,we have concluded that our solution can effectively solve the problem of skyrmion's deviation,and has a high theoretical upper limit,which can make skyrmions reach an extremely high motion speed.At the same time,this method has lower requirements for skyrmions' generation and detection conditions.Finally,we summarized the current work and looked forward to the future work.