| Magnetic Skyrmion has the characteristics of fast motion under ultra-low current density,so it has potential application in future storage devices.From the point of view of application,the research on magnetic Skyrmion faces the following challenges:it is difficult to obtain a long-term stable Skyrmion phase under room temperature and zero external magnetic field;there is no effective method to control the size of them;and Skyrmion moves at a low speed under the current drive now.In view of the above problems,the main research contents of this paper are summarized as follows.1)The generation of magnetic Skyrmions has been realized experimentally.In Pt/Co/Ni/IrMn and Ta/CoFeB/MgO systems,the Skyrmions were produced at room temperature,respectively.Firstly,in the presence of an external magnetic field,the Skyrmions were observed in the Pt/Co/Ni/IrMn system with weak perpendicular magnetic anisotropy.By the same method,the occurrence of Skyrmions in Ta/CoFeB/MgO system with strong magnetic anisotropy was also observed successfully.At the same time,the effect of stray magnetic field from the magnetic probe itself was noticed,and the magnetic Skyrmions of remanence state were successfully produced by means of the magnetic probe scan.The experimental results show that Skyrmions produced by this method can be stable at room temperature for a long time.Finally,the magnetic Skyrmion lattice was successfully observed at both room temperature and zero external magnetic field by applying an inclined external magnetic field to the sample.Each Skyrmion is surrounded by the other six.Temperature measurements show that the Skyrmion lattices are very stable,and can even exist at room temperature for more than 30 days.In addition,the temperature measurement results also show that the lattice structure can even withstand 350 K high temperature to a certain extent.2)The structure of magnetic Skyrmion in multilayer films was simulated by micromagnetism.The results show that in the multilayer system Ta/CoFeB/MgO,Skyrmion tends to exhibit a Néel-Bloch hybrid structure.The magnetic structures of the top and bottom layers of the multilayer films show a Néel type,and then gradually transit to a Bloch structure in the middle layer.Furthermore,by changing the direction and size of the external magnetic field,we can effectively control the size of the Skyrmion.3)Regulation and control of magnetic Skyrmions.Using Ta/CoFeB/MgO system,the effect of the thickness of heavy metal layer on the size of Skyrmion was studied.In a certain range,the magnetic anisotropy constant K is adjusted by changing the thickness of heavy metal layer and keeping the Dzyaloshinskii-Moriya interaction constant D with exchange constant A unchanged.Four films,tTa=1.0,1.8,2.5 and 5.0,were selected in the experiment.The maximum anisotropy constant of tTa=1.0 film is2.4×105 J/m3.The average diameter of the Skyrmion is 160 nm,and some of them even less than 100 nm.It show that the size of the Skyrmion can be controlled effectively without using the external magnetic field.In addition,by adjusting the thickness of CoFeB,the transformation from disordered Skyrmion states?Skyrmion glass states?to multi-domain Skyrmion lattice states can be realized.In thicker ferromagnetic layer samples,the interface is smoother and there are fewer defects,which is more conducive to the formation of the ordered state of Skyrmion.Finally,the“reversal”ofSkyrmion lattice is realized by using an external tilted magnetic field.This reversal comes from the disappearance of Skyrmion and the nucleation and growth of the polarized opposite Skyrmion in the interstitial positions of lattice.After flipping,the new lattice state can still exist stably.Subsequently,the results of micromagnetic simulation further confirm this phenomenon. |
PDF Full Text Request