Ultrafast Magnetoelectric Effects Of Topological Magnets

The topological magnetic structure is very promising to become the basic unit of high-density non-volatile magnetic memory,information processor,sensor and other new functional devices based on topological defects because of its numerous advantages,such as high thermal stability,small size and various state characteristics,so as to solve the performance bottleneck of current magnetic devices.The research on the magnetoelectric properties and the electric field controllability of the topological magnetic soliton can not only make us have a deeper understanding of the topological phase transition of the magnetic structure,but also provide a new development idea for the next generation of spin electronic devices.Benefiting from the non-collinear distribution of the magnetic sequence in the topological magnetic structure and the induced magnetoelectric interaction,based on the inverse-Dzyaloshinskii–Moriya mechanism,we have realized the ultrafast,stable and repeatable electrical control of topological magnetic solitons by applying electric field and terahertz pulse,which provides an important theoretical support for the application of magnetic solitons(magnetic Skyrmion and vortex).1)The electric field regulation of multiferrous Skyrmion.The lack of spaceinversion symmetry at the ferromagnetic / ferroelectric interfaces opens up a physical channel for the electric field control of the Rashba spin-orbit coupling effect and the Dzyaloshinskii–Moriya interaction,and also provides a way to realize the electric field manipulation of the multiferroic Skyrmion dynamics at room temperature.In this paper,we first analyze the electric field driven phase transition evolution of the spin structure at the ferromagnetic/ferroelectric interfaces,and give the conditions for the existence of stable Skyrmion lattice.Furthermore,the chirality,polarization,radius,position and the number of Skyrmions are controlled by adjusting the applied electric field appropriately.We also describe the anisotropy and inhomogeneity of the Skyrmion lattice dynamic multiferrous response in the microwave field,and give the magnetoelectric resonance spectrum of Skyrmion lattice.2)The ultrafast electric field conversion of ferromagnetic vortex.In recent years,the rapid development of terahertz technology have provided a favorable experimental condition for us to realize ultrafast and all-optical control of magnetic structure.By applying a simple picosecond electric field pulse sequence,we propose a new mechanism for the state transition of magnetic vortex mediated by packaged-Skyrmion.Different from the generation and annihilation process of vortex-antivortex pair,this new state switching mode avoids the damage of vortex structure and shortens the time of polarization reversal to about 15 ps.By using the time-sequence asymmetric Gaussian laser pulse,we also can realize the ultrafast switching of vortex chirality without destroying the rotational symmetry,and the control time is greatly shortened to 350 PS.The polarization and chirality of vortex can even be reversed at the same time by adjusting the pulse width properly.The ultrashort dynamic switching process allows us to further explore the reproducible control of the vortex state,and the simulation result shows that no matter polarization control,vortex chirality reversal,or even both of them switching at the same time,all of them have shown a stable control process even under 40 pulses.The electrical control of magnetic vortex dynamics in a repeatable way and an ultrafast time scale provides a very important opportunity for seeking low-energy consumption and high efficiency spin electronic devices.3)The track effect of package-Skyrmion.As a mediated state in the switching process of magnetic vortex,the packaged-Skyrmion can be stabilized and trapped in a strip by the magnetoelectric coupling.Due to the force which originates from a slight offset between the packaged-Skyrmion center and the Gaussian laser beam center in the vertical direction can balance the effect of Skyrmion Hall effect,the packaged-Skyrmion will be allowed to move at a maximum velocity of 80m/s in the horizontal direction.The excellent grasping ability of Gaussian electric field on packaged-Skyrmion enables it to make nearly energy-free circular motion in square magnetic lattices.As a result,the packaged-Skyrmion not only can be used in transistors and logic devices,but also can be used as a spin nano-oscillator to generate GHz AC signals and above.The ultrafast and reliable electric field regulation of topological magnetic solitons has a wide application value not only in the traditional information storage direction,but also in other fields,such as neural network,magneton and spintronics computing fields.