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

Aftereffect for magnetization processes by rotation and by domain wall moti on was investigated on the same, single domain, two-state system of a squar e 2D (two-dimensional) array of garnet particles. Aftereffect measurements were performed magnetooptically. The particles are thermally stable, the pa rticle 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" magne tized particles could be observed at room temperature. At increased tempera tures thermally activated switching, very weakly depending on magnetic fiel d, is observed. Each individual particle can be demagnetized into a metasta ble stripe domain structure. The barrier for DW (domain wall) motion is muc h lower than the barrier for rotation, and a significant aftereffect was me asured on the same particles, demagnetized into a domain structure. The obs erved 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. [S0021-8 979(00)61308-7].