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 magnet ic dots has been measured and simulated. Arrays (50 x 50) with perpendicula r magnetized Co dots (2 mum x 2 Am) were patterned using a high resolution Cia' focused ion beam irradiation. Magnetic domain pattern and time relaxat ion of the dot arrays were investigated using Faraday magneto-optical micro scopy. For arrays designed with high irradiation doses (greater than or equ al to0.5 nC/cm), the magnetic relaxation of the array proceeds by the magne tization reversal of individual dots and follows a power-law time decay. Th e long-range character of the dipolar interaction is found to be responsibl e 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 t he boundary of the arrays, and it is independent of the shape of dots as we ll.