Skyrmion In Chiral Magnets And The Dynamics Of Skyrmion

A Skyrmion is a topological excitation which was first proposed by Skyrme, protected by topology, and later was observed in many condensed matter systems. Skyrmions were also predicted to be stable in chiral magnets, where the inversion symmetry is broken. Many ways contribute to the motion of Skyrmion, additional electric as well as additional magnetic, opening the way of manipulation of spin textures in the field of spintronics. But the underlying mechanisms of stable Skyrmion in spin systems are still unknown, and there are still many spaces left to study the dynamics of Skyrmion.In the first introductory chapter of this Thesis, we will briefly review the meaning of topology, and its development in physics, especially in condensed matter physics.In the second chapter, we review the discovery of the Skyrmion lattice in MnSi, where we introduce the different magnetic phases of MnSi and their relations with temperature and external magnetic, both experimentally and theoretically. Another essential progress concerning experiments is that the Skyrmion lattice cannot only be observed in momentum space by neutron scattering, but also in real space using Lorentz transmission electron microscopy in thin films. Besides, we talk about the dynamics of Skyrmions. we first study their current induced dynamics, i.e. the translational motion, and we talk about Skyrmion motion induced by the spin Seebeck effect. We also show that a thermal gradient can be used to move magnetic Skyrmions in insulating chiral magnets.In the third chapter, we will first discuss the Skyrmion Model in the CP1 formulation of the nonlinear sigma model, we find an isolated Skyrmion in two dimensions with the spin pointing down at the origin r= 0 and up far away r→∞ is given by the CP1 expression. Besides,we study the free energy of helical pahse, Skyrmion phase and ferromagnets with the external magnetic field, and the transition between them.In the fourth chapter, we mainly study the stablizing factors of helical and Skyrmion spin texture in the PMN-PT heterostructures, and the effect of polarizations. We arrive to control these spin texture with electric filed.Lastly, we make a summary about our work, and talk about the prospect of Skyrmion.