Simulation On Micro And Nano Structures Of Magnetic Material

Recently, magnetic materials have been widely used in the industry and our daily lives. Over the last decade, with the continuous improvement of micro-fabrication, micro and nano structures had been widely used in various fields due to its low power consumption, highly integrated and many other significant advantages. Therefore, research on magnetic materials have gradually turned to magnetic micro and nano structures. This thesis mainly focus on the study of controllable switching the circulation and polarity of magnetic vortices, and the study of spin wave modes of artificial Skyrmion lattice crystal.We report a method to switch both the circulation and polarity of magnetic vortices in a controlled manner within a nanosecond utilizing micromagnetic simulations. The controllable switch is achieved with the combination of two different types of magnetic field pulses on submicron permalloy disks with heptagonal shape. When a magnetic field pulse of～100 mT is applied along one of the edge directions of the heptagon, the circulation of the vortex can be manipulated according to the pulse direction. When a pair of pulses with a few tens of mT in magnitude and relative delay of about 100 ps is applied in orthogonal directions, the polarity can be further controlled without influencing the circulation. The different magnitude of switching fields allows for the combination of both types of pulses in the control of both the circulation and polarity of magnetic vortices. The switching mechanism and the controlling parameters for disks with diameters of 500 and 700 nm are discussed.Utilizing mcromagnetic simulation, we study the spin wave modes of the artificial Skyrmion lattice which we reported before. This kind of Skyrmion is formed with a combination of a perpendicularly magnetized film and nanopatterned arrays of nanoscale magnetic vortices. We first expore the resonant frequencies by apply a Gaussian shaped pulse field along x and z directions to the Skyrmion crystal, respectively, and there are four resonant frequencies. Afterwards, we trace the spin dynamics by applying a stationary oscillating magnetic field to the Skyrmion crystal. It turns out the first lower frequency modes are the in-plane modes, and the higher frequency modes are the out-of-plane modes, the breathing modes. We study the Skyrmion lattice crystal with Skyrmion number of both +1 and -1 to make a comparison. We find out that their spin wave modes are basically the same, and under the same oscillating field, those two kinds of Skyrmions show opposite vibrational states at the same time.