H/sub c/ measurement of microscopic regions on thin film magnetic disc using longitudinal Kerr effect

A longitudinal Kerr magnetooptical microscope system with a read/write testing unit and a positioning unit was developed for nondestructive measurement of the coercive force (Hc) in thin-film magnetic disks. This system measures the magnetooptical hysteresis loop from an area 2-30 mu m in diameter on a disk with a C/CoNi/Cr layer. The magnetic field strength at the disk surface was estimated from the coil current in a Weiss-type magnet. The absolute value of the field strength was calibrated by a Hall sensor. The actual H/sub c/ values were measured and compared with the result obtained by a vibrating sample magnetometer in order to determine the accuracy, which was found to be within 2%. It took 36 min. to complete the H/sub c/ measurement at 144 points over a 5.25 in. disk for a mean spot size of 30 mu m.<
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