Dynamics Of The Antiferromagnetic Domain Wall

Since human beings entered the information age represented by computers,all walks of life are based on a large number of data to assist decision-making,analyze the reasons,predict and make a plan,etc.Massive data is becoming more and more demanding on the miniaturization,inversion and storage capacity of storage devices such as hard disk,disk and so on.These problems have driven the development of spintronics.In the ferromagnetic materials used in traditional memory devices,due to the dipole interaction,the memory cells have a great influence on each other.If the magnetic memory is based on antiferromagnetic materials,it will resist the disturbance of electric charges and magnetic fields.At the same time,antiferromagnetic materials also have the advantages of being insensitive to external fields,zero net magnetization,high operating frequency,and rich variety.The magnetic domain wall is a very basic concept in magnetism and an important object for studying spintronics.The study of the law of domain wall motion can not only deepen the understanding of macro-magnetism,but also have wide application value.In recent years,researchers have proposed a variety of methods for manipulating antiferromagnetic domain walls,for example,spin transfer torque,spin wave,spin orbit torque and thermal gradient.However,the mechanism of antiferromagnetic domain wall motion is not completely clear.Moreover,finding a new method for effectively manipulating antiferromagnetic domain walls is still the key to studying antiferromagnetic domain walls.In this thesis,through numerical simulation based on the atomic spin model and the corresponding theoretical analysis,we mainly study the dynamic phenomena of the antiferromagnetic domain wall under the rotating magnetic field and spin transfer torque.Our conclusions are as follows:(1)In one-dimensional antiferromagnetic nanowires,we studied the motion law of antiferromagnetic domain walls under a rotating magnetic field.We find that Dzyaloshinskii-Moriya interaction(DMI)plays a key role in the movement of the domain wall.The rotating magnetic field cannot drive the antiferromagnetic domain wall without DMI.We find two modes of antiferromagnetic domain wall motion: first,fully synchronized regions,in the lower frequency range of the rotating magnetic field,the rotation of the antiferromagnetic domain wall is perfectly synchronized with the rotating magnetic field.The steady velocity of the antiferromagnetic domain wall depends only on the frequency of the rotating field and the ratio between DMI strength and exchange constant.And it is independent of the damping and the rotating fields trength.Second,in the higher frequency range of the rotating magnetic field(corresponding to the incomplete synchronization region),the motion of the antiferromagnetic domain wall is an oscillation mode,similar to the Walker breakdown phenomenon of the ferromagnetic domain wall.(2)We study the motion law of antiferromagnetic domain wall under spin transfer torque.We find that the direction of the spin polarization current is very important.For example,when the polarization direction is consistent with the direction of the nanowire,the antiferromagnetic domain wall does not move,but simply rotates.We use numerical simulation and theoretical analysis,we find that the flipping of the domain wall is only related to the damping and current intensity.It is proportional to the current density and inversely proportional to the damping.(3)Based on the pure rotation mode of the antiferromagnetic domain wall,if the applied current exceeds the critical current,the helix wave can be excited with the domain wall as the starting point.If the current is only applied to the domain wall,the amplitude of the helix wave will be attenuated at a position far away from the domain wall.We use a local current to control the amplitude of the helix wave.When the polarization direction of the applied local current is the same as the polarization direction of the current at the domain wall,the amplitude of the helix wave is significantly strengthened.Conversely,the amplitude of the helix wave decreases.The helix wave can be left-handed rotation or right-handed rotation.According to this feature,we can design a Y-shaped logic gate: AND gate and OR gate.