Dynamic magnetization properties of a superferromagnetic metal-insulator multilayer observed by magneto-optic Kerr microscopy

Longitudinal magneto-optical Kerr effect (MOKE) magnetometry and microscopy have been performed on a superferromagnetic (SFM) metal-insulator multilayer of [ Co 80 Fe 20 ( t n = 1.3 nm ) / Al 2 O 3 ( 3 nm ) ] 10 to understand the dynamic behavior of the SFM domains. Frequency dependent hysteresis loops measured by MOKE show that the coercive field H c increases as the rate (frequency) of magnetization reversal is increased similar to dynamic hysteresis loops observed on conventional ferromagnetic ultrathin films. This dynamic hysteresis behavior arises due to SFM friction-controlled domain wall motion which is observed by MOKE microscopy. We see that the nucleation field for SFM domains increases for hysteresis loops with higher frequency as expected for a ferroic system.