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Technology Stocks : Disk Drive Sector Discussion Forum
WDC 140.23-8.9%Nov 20 3:59 PM EST
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To: T Bowl who wrote (2750)3/9/1998 2:58:00 PM
From: Stitch  Read Replies (2) of 9256
 
T-Bowl, Bill Lin;

Todd, HMT's reference is excellent but you are intuitively right about correlating areal density with coercivity. It will vary from process to process. It depends, on other characteristics such as called remanence thickness (or BRT), magnetic domain orientation, and its anisotropic characteristics. This latter two dollar buzz word refers to the individual magnetic domain and means the opposite of isotropic. In plain English it means the domains must display a characteristic of more longitude then latitude for pole definition. Each domain is a magnet with a south pole and a north pole...thus it represents a bit that can be reversed [coerced] from positive to negative. These bits must also be separate and distinct to avoid cross fringing interference or adjacent bit interference. As coercivity goes up each bit requires more external force in order for it to be reversed from a positive to a negative. This is desirable when you are crowding more and more bits in the same space so as to prevent them from interfering with one another and only responding to the external force designed (as in write amplitude from the head). Thus coercivity is one of the key elements of higher densities. The remanence mentioned has to do with the nature of the domain to stay reversed, or rather the remaining amount of magnetic flux after a write operation. There is always some loss due to hysteresis and eddy-current losses in the write head. This is largely dependent on the thickness of the film so is expressed as an equation of remanent flux and thickness. Hope this is more then you want to know cause it is all I know.

Best,
Stitch
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