Micromagnetic Simulations Of Magnetic Dynamics In Magnetic Nanostructures

Magnetic dynamics of magnetic materials gradually developed from the last century has been one of the popular subjects focused by scientists.The magnetization reversal and domain wall motion in recent years have been in a lot of discussion,which have great potential applications in the next-generation of information storage.During rapid development of today's information age,production of high read/write speed and density of magnetic storage devices presents a great challenge to people.The technologies for fast memory of information and high-density storage have more urgent requirements.Magnetization switching process in real materials is quite complex.Current science and technology also allow researchers to macroscopically observe the change process of magnetic moment under certain conditions.Moreover,uniaxial magnetic particles and many-body systems are often studied in theory and simulation in order to guide applications.In addition,the domain wall propagation in magnetic nanowire also can be used in vertical storage to read and write for the next-generation memory devices.In this thesis,we observed the magnetic dynamics of magnetic two-body systems and head-to-head magnetic domain wall through the OOMMF micromagnetic simulation tool,with a view of a guiding role to the related work.First of all,we describe what spintronics is and explain its related phenomena and concepts in detail,and introduce the theory of micromagnetism.In addition,we also introduce the micromagnetism simulation tool,OOMMF,used in many fields.Later,on the basis of micromagnetic theory and Landau-Lifshitz-Gilbert(LLG)equation,we simulated the magnetization switching of the Stoner particle two-body system.We achieved the ultralow critical flip field in a critical spacing through changing the spacing between the two particles in perpendicular(PERP)configuration,which is consist with the zero-field switching theory.In addition,the achievable results when we change the radius of particles in system also meet our earlier analytical theory.Due to the effectiveness of Stoner particles' radius,the relationship between critical radius and critical spacing is valid only in small range.Then,we simulated the head-to-head domain wall's propagation behaviors induced by static field and microwave field in magnetic nanowires.The domain wall motion velocity is almost proportional to static field.When the external field is increased to a certain value called Walker breakdown,the maximum domain wall motion velocity can be obtained.Increasing field,domain wall will oscillate back and forth,which results in decreasing domain wall speed with the increasing field.The results is consistent with the well-known Walker theory.Moreover,we also simulated the domain wall motion driven by microwave field set on the nanowire's section area.Domain wall movement speed increases with microwave amplitude in a settled frequency.When the amplitude of microwave field is fixed,an unexpected result occurs when changing microwave frequencies.Domain wall motion speed increases with frequency at first until a frequency window appears in which domain wall occurs deformation and no stable of domain wall structure exists.Then domain wall spreads along the opposite direction,and speeds decrease with frequencies and gradually reduces to zero.Finally we have a summary of this thesis,and puts forward some problems needed to be solved in future and an outlook about related researches.