Power-law relaxation decay in two-dimensional arrays of magnetic dots interacting by long-range dipole-dipole interactions -: art. no. 184440

The magnetic relaxation of two-dimensional arrays of dipolar coupled magnetic dots has been measured and simulated. Arrays (50 x 50) with perpendicular magnetized Co dots (2 mum x 2 Am) were patterned using a high resolution Cia' focused ion beam irradiation. Magnetic domain pattern and time relaxation of the dot arrays were investigated using Faraday magneto-optical microscopy. For arrays designed with high irradiation doses (greater than or equal to0.5 nC/cm), the magnetic relaxation of the array proceeds by the magnetization reversal of individual dots and follows a power-law time decay. The long-range character of the dipolar interaction is found to be responsible for magnetic relaxation with a power-law decay. Monte Carlo simulations, based on a modified Ising Hamiltonian, reproduce this time dependence, and show that the power law is not a consequence of either the finite size or the boundary of the arrays, and it is independent of the shape of dots as well.