Study Of Magnetic Dynamic Properties For Nanorings

Magnetic nanorings can be integrated with high density for the system having few stray field when they are in votex state.So,they will be good magnetic recording materials.In addition,nanorings have broad application prospects in biomedical and sensor fields.It is still a challenge to simulate the magnetic properties of the system quickly and efficiently for the nanorings.In this doctoral thesis,based on Monte Carlo method combining the fast Fourier transform micromagnetism method,the magnetic properties for the large scale systems have been calculated,which overcome the disadvantages of the traditional Monte Carlo method in the simulation of the dipole energy,such as long calculation time and low efficiency.The magnetic dynamic properties of the following nanorings are studied as follows:(1)The magnetic properties of the defective Co nanorings.Two kinds of defective Co nanorings are constructed: nanorings with eccentric circular defect and clipped nanorings.The magnetization processes of the cobalt nanorings with two kinds of defects are similar to that of the symmetrical system when the defect degree is small.When the defect degree increases,the magnetization behavior of the system is different from that of the symmetric system.Moreover,the shape,size and location of defects have significant influence on the magnetic properties of the systems.The simulation results are consistent with the experimental data.(2)The magnetic properties of the defective Fe nanorings.Two defective forms of Fe nanorings are constructed: eccentric nanorings and nanorings with eccentric circular defect.The defects of the two kinds of iron nanorings(such as the degree of eccentricity,defect area,location,etc.)have obvious influence on the magnetic properties of the system.When the defect degree is small,the magnetization behavior is similar to that of symmetric system.When the area of defect increases,the magnetization behaviors of the system show new properties.The simulation results are similar to the experimental data.(3)The magnetic properties of the double Co nanorings array.When the distance between the centers of the double nanorings system is large enough,the magnetic properties of the system are close to those of the single nanoring.However,with decreasing center distance,the hysteresis loops of the system display a bistable characteristic,which are similar to that of the single nanoring.But,their spin configurations are different from those of the single nanoring.Moreover,the hysteresis loops of the double-ring array system with different spacing are obviously different,and their votrx states show more abundant properties.The simulation results are close to the experimental data.(4)The magnetic properties of the nanoring system based on the reduced magnetic parameters.In order to study other nanoring magnetic materials extensively,reduced magnetic parameters are introduced.It is found that the systems present bistable properties under proper reduced parameters,and the magnetic and geometric parameters of the systems have obvious influence on the magnetic properties of the nanoring systems.At last,the above magnetization dynamics properties can be explained by analyzing the spin configuration and the energy competition mode of the systems.