Time decay of the magnetization of the arrays of Permalloy circular dots of submicron sizes was measured on a long time scale (hours) near the vortex nucleation field. A considerable influence of external magnetic field and temperature on the slow magnetization dynamics was detected. The observed effects are explained by overcoming the field dependent energy barriers in the process of vortex nucleation. The magnetic viscosity and energy barriers were found from the magnetization time decay dependencies.
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