Research On The Dynamics And Application Of Nano Magnetic Domain Structure

The discovery of the giant magnetoresistance effect in 1988 marked the establishment of spintronics.In the last 30 years,magnetic sensors and high-density information storage based on spintronic devices have made rapid progress.Compared with traditional hard disks,magnetic racetrack memories based on magnetic domains?such as magnetic domain walls and magnetic skyrmions?can greatly increase the storage density of the devices.The magnetic domain refers to a region with a uniform magnetization inside a magnetic material,In each magnetic domain,the arrangement of atomic magnetic moments has a spontaneous tendency to be parallel to each other,and the direction of the magnetic moments remains consistent.At the boundary of the magnetic domain,the magnetic moment continuously transitions from one direction to the other,thereby forming a magnetic domain wall.Magnetic domain is one of the typical characteristics of magnetic materials.Generally,the presence of magnetic domain structures in materials is mainly to reduce the demagnetization energy.Magnetic skyrmion is a chiral spin texture with local non-colinear spin arrangement.This spin config is topologically protected and therefore abnormally stable.This thesis mainly uses the method of micromagnetic simulation to study the dynamic regulation of magnetic domain-chains in magnetic nanowire and the related problems of terahertz signal generators based on magnetic skyrmions.?.Dynamic nucleation of domain-chains in magnetic nanotracksIn this section,we propose a simple and effective solution for injecting multiple magnetic domains into magnetic nanowires to form magnetic domain-chains.Through micromagnetic simulation,we found that the frequency of the microwave field and the period of the spin polarization current intensity can be used to dynamically regulate the number of single domains in the magnetic domain-chain,and the frequency of the microwave field and the intensity of the spin polarization current can dynamically control the static characteristics of magnetic domain-chains,that is,their length,interval,and period between adjacent magnetic domain-chains.This provides a meaningful solution for flexible multi-bit information storage applications.We found that:?1?When the frequency f of the microwave field is reduced from 8.0 GHz to 0.5 GHz,the number N of magnetic single domains contained in each magnetic domain-chain,the spatial period P of the magnetic domain-chain,and the interval between adjacent magnetic domain-chains S will increase.When the frequency of the microwave field is fixed at f=8.0 GHz,each magnetic domain-chain contains only one magnetic domain,that is,P=S.?2?Only when the spin polarization current intensity u>1000 m/s can drive the nucleated magnetic domain chain move along the nanowire.Therefore,we can encode a series of complex magnetic domain-chains composed of magnetic domain-chains each compriesd of different numbers of magnetic domains by encoding the variation of spin polarization current intensity with time.?3?Both the frequency f of the excitation microwave fields and the temporal format of the spin polarization current intensity u can obviously affect the typical characteristics of generated domain-chains:the number N of individual domains in each domain-chain,the period of domain-chains,and the distance between adjacent domain-chains.?.An on-chip electrically tunable THz signal generation based on magnetic skyrmion motionIn this section,we propose a terahertz signal generation method for integrated chips based on magnetic skyrmions.The micromagnetic simulation was used to study the dynamic behavior of magnetic skyrmions driven by spin transfer torque.The research found that the main factors affecting the frequency of terahertz signals include:?1?The frequency of a terahertz signal is linearly dependent on the strength of the spin polarization current intensity u.When u increases from 1×10¹⁰m/s to 5.5×10¹⁴m/s,the signal frequency f₀/f₁/f₂ increases about 0.69/0.14/2.06 THz.?2?The THz signal frequencies are highly dependent on the skyrmion lattice d.For instance for d=50/100/200 nm,u=2.0×10¹⁴ m/s,f₀=0.50/0.25/0.12 THz,f₁=0.99/0.50/0.25 THz,and f₂=0.49/0.74/0.37 THz.?3?The frequency of the terahertz signal is independent of the external magnetic field H_z,Dzyaloshinskii–Moriya interaction D and nanotrack length L.When the size S of the magnetization detection area is increased from 4 nm to 160 nm,the center frequency of the terahertz signal remains unchanged.On the contrary,the strength of the terahertz signal decreases significantly with increasing S.