Reading dynamics in Front Aperture Detection (FAD) MSR media

Front Aperture Detection (FAD) makes possible the detection of domains smaller than the optical diffraction limit and thus achieves magnetic super resolution (MSR) in magneto-optical (MO) recording. The success of this detection technique depends on good control of the shape and relative position of the thermal mask during the reading process. To have a better understanding of the reading dynamics in FAD, a high speed Kerr microscope system with 10 ns resolution built on an air bearing spin stand was used to directly observe the dynamics of the thermal mask and the effective aperture in FAD disks during readout. A computer simulation of the thermal profiles was compared with the experimental results and provides insight to the data analysis. It is shown that reading power, bias field and linear velocity affect the length of the thermal mask and the effective reading aperture. This effect strongly depends on the temperature gradient. Adding an Al underlayer to sharpen the thermal profile can reduce the dependence of the effective aperture on small changes in power and bias field during reading