Lateral homogeneity test of CoCr disks using the Kerr magneto-optical effect

Lateral homogeneity of the magnetic properties of a CoCr layer sputtered on a disk may be a problem. By using the Kerr magneto-optical effect the lateral homogeneity of a disk can be measured without destroying the disk. An apparatus is described which measures the magneto-optical hysteres is loop at a certain number of spots forming a grid on the disk. For each hysteresis loop, representing the properties of an area with about 1 mm in diameter, the magnetic parameters relevant for vertical magnetic recording are determined by using fitting procedures. The parameters are coercivity, saturation Kerr rotation and squareness. The calculations are performed by the computer controlling the apparatus. After all spots have been measured, the computer calculates and draws a picture of the lateral dependence of each parameter. The results of inhomageneous disks are compared with results from write/read tests on the same disks. Azimuthal and radial variations in the output voltage can be attributed to local inhomogeneities in coercivity or squareness.