Thickness-dependent evolution of magnetization reversal in coupled permalloy nanocaps

The magnetization reversal mechanisms in permalloy (Py) nanocaps, coupled through an indirect exchange interaction, were investigated using micromagnetic simulations. This indirect exchange interaction can oscillate between ferromagnetic and antiferromagnetic types, depending on the thickness of the metallic interlayer. In ferromagnetically coupled Py nanocaps, coordinated nucleation and annihilation of magnetic vortices were observed. On the other hand, antiferromagnetically coupled caps exhibited a coherent rotation of spins, stabilizing a double onion state at remanence. The study also investigated the impact of nanocap thickness on the magnetization reversal process. As the thickness of the Py cap increased, the magnetization reversal displayed characteristics typical of a weakly coupled system. This shift in magnetization reversal behavior is attributed to the relative decrease in exchange coupling strength between the nanocaps as their thickness increases.