Rotational and domain wall motion aftereffect in a patterned array of small particles

Aftereffect for magnetization processes by rotation and by domain wall motion was investigated on the same, single domain, two-state system of a square 2D (two-dimensional) array of garnet particles. Aftereffect measurements were performed magnetooptically. The particles are thermally stable, the particle energy is 10(-6) erg compared to the thermal energy of 10(-12) erg. No aftereffect of rotation switching of the system of "up" and "down" magnetized particles could be observed at room temperature. At increased temperatures thermally activated switching, very weakly depending on magnetic field, is observed. Each individual particle can be demagnetized into a metastable stripe domain structure. The barrier for DW (domain wall) motion is much lower than the barrier for rotation, and a significant aftereffect was measured on the same particles, demagnetized into a domain structure. The observed time dependence for DW aftereffect is exponential, M(t)/Ms=d* exp(-et), where d=0.04, and e=1/tau follows the increase of the magnetization with field, de/dH=0.021 /s/Oe. (C) 2000 American Institute of Physics. [S0021-8979(00)61308-7].