| The novel physical phenomena in non-collinear spin textures of magnets have received more and more attentions.Magnetic skyrmion,as topologically stable spin-swirling object with particle-like properties,has been found in many non-centrosymmetric chiral magnets like B20-type compounds(MnSi,FeGe,Fe1-xCoxSi).Due to the low-energy control of single skyrmion and the prominent microwave diode effect owing to the interference of magnetic and electric responses,skyrmions are believed to be used in the next generation of new memory,logic and microwave devices.In the first chapter,the related experimental research background has been briefly introduced,including the basic concepts and observation of skyrmions.In the second chapter,we have primarily focused on the theoretical background of micromagnetics,including the classical Heisenberg spin model widely used to calculate the structure by Monte-Carlo simulation,and the Landau-Lifshitz-Gilbert for studying the spin dynamics driven by current and magnetic field.In the third chapter,we use the spin model and Monte-Carlo simulation to get the spin structure and magnetic field-temperature（B-T）phase diagram of chiral magnets like MnSi.There are three different non-collinear spin textures（helical phase,conical phase and skyrmion phase）in three-dimensional（3D）cubic lattice,while the conical phase is suppressed and replaced by skyrmion phase in two-dimensional（2D）lattice because the spins cannot complete the spiral along the magnetic field.In the fourth chapter,we use the LLG equation to study the spin dynamics.The enhanced magnetic resonance of skyrmions occurs in oscillating magnetic fields at specific frequency,such as the breathing mode of skyrmion with out-of-plane magnetic fields,and the counterclockwise and clockwise rotational modes with in-plane magnetic fields.Skyrmions can be driven by ultralow current and its velocity is proportional to the current density.The adiabatic spin-transfer torque dominate the velocity parallel to the current,while the non-adiabatic spin-transfer torque has strong influence on the velocity perpendicular to the current.In the fifth chapter,we summarize our present work briefly. |
