Micromagnetic simulation of magnetic switching behavior of permalloy nanocap thin films

Magnetic hysteresis loops of Permalloy nanocap thin films fabricated on top of nanospheres are simulated using MuMax3, a micromagnetic simulation program, to study the magnetic switching behavior of curved magnetic thin films. Four different shapes are introduced to construct a single nanocap used in the simulation. For a given shape, various thicknesses of the nanocap with a fixed diameter of nanosphere, and various diameters of nanosphere with a fixed thickness of the layer were studied in the simulation. Simulation results were compared to investigate how the thickness (t), diameter (d), and the ratio of t/d will change the magnetic switching behavior of nanocap thin films. Hysteresis loops showed more drastic change with varying the thickness compared to the diameter. Based on the comparison among the different shapes the one showing the hysteresis loops with well-defined coercivity was chosen and further simulations on extended shapes were made. Seven nanocaps in a hexagonal pattern were simulated to observe how the interaction among the nanocaps changes the magnetic switching behavior of the system. The formation of magnetic vortices was more likely to happen in seven nanocaps. The orientation of the vortices on the top and bottom rows were influenced by the direction of the magnetic moment of the middle row in the hexagonal pattern. Also, there were two different chirality were observed in the magnetic vortices. To remove the edge effect, seven nanocaps were extended to a grid pattern that maintains the self-assembled pattern with periodic boundary conditions. It was found that magnetic vortices were formed when there was interaction among the nanocaps and neighboring vortices were interacting along the hysteresis loop.