Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Patent
1988-01-13
1989-06-27
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
324202, 324212, 324223, 324225, G01R 3314, G01R 3500, G01N 2772
Patent
active
048433160
ABSTRACT:
The manufacture of digital magnetic recording discs for computer disc drives requires the monitoring and control of the M-H hysteresis loop properties of the magnetic film deposited on the disc substrate. Several methods exist for measuring this M-H hysteresis loop, but they all have serious disadvantages. One method consists of cutting samples and measuring them with a vibrating sample magnetometer. This is a destructive test and requires a lot of time per sample. Another method uses the Kerr-rotation of polarized light. However, it samples only the mangetization of the surface and cannot determine the magnetic thickness of the film. A third method magnetizes the entire disc and samples a large region along a diameter. This method cannot distinguish between the top and bottom films of the disc, and cannot resolve circumferential variations of th M-H loop properties. The method of this invention solves these problems by measuring a small part of one surface of the disc nondestructively using a special balanced head having two air gaps. It is fast, requiring only about 2 minutes per measurement and has good reproducability.
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Hoel, J. E. Magnetic Reluctance, Film Thickness Gauge, IBM Tech. Discl. Bull. vol. 13, No. 10, Mar. 1971, pp. 3048-3049.
Hand Saundra H.
Hewlett--Packard Company
Howard William H. F.
Strecker Gerard R.
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