Rotational aftereffect of single domain particles

The time sequence of individual switching events was measured between 50/spl deg/C and 88/spl deg/C in an applied field H*, on a two dimensional square array of single domain garnet particles, switching by rotation against anisotropy energy barriers. The system is stable against thermal excitation because there are no low energy domain wall (DW) processes present, and no thermal aftereffect takes place at room temperature. However, at elevated temperatures the anisotropy barriers are decreased, and thermal relaxation by rotation was observed. In the regime of rotational switching the thermal relaxation process depends very weakly on the magnetic field. The aftereffect can be described by n(t)=n/sub 0/(1-exp(-t//spl tau/)). At T=50/spl deg/C, /spl tau/=(77/spl plusmn/7) s, decreasing to (24/spl plusmn/4)s at 88 C. As expected, at a given temperature /spl tau/ is practically independent of H*, demonstrating that, in contrast to aftereffect in materials involving DW motion, the aftereffect in two dimensional arrays, switching by rotation, is not sensitive to the applied field.