COMPUTER-SIMULATION OF MAGNETIZATION REVERSAL IN FINE HEXAGONAL PLATELET PARTICLES WITH DEFECTS

The Landau-Lifshitz-Gilbert equation is used to investigate the switching fields and mechanisms of fine hexagonal platelet particles which have three types of defects in comparison with a nondefect particle. Two of the defects are surface defects, one with an area more than 50% of the hexagon and the other much less than 50%. The third defect is not a surface defect but a defect which extends from the top to bottom surface. The differences between the switching fields of these particles are small, at most 12%. The angular dependence of the switching fields of these particles is similar to the ones derived from the coherent rotation mode. The switching mechanisms of the particles change with applied field. The nondefect particle switch in a normal vortex mode and the particles with defects switch in a mixture of normal vortex and coherent rotation-like mode at the applied field = H(sw) (switching field). Most of them switch in a twisted vortex mode at the applied field = 3 X H(sw). But in surface defect particles, whose defect area is more than 50% of the hexagon, the switching mechanism hardly changes from a coherent rotation-like mode.