In recent years, the areal density of hard disk drives has been increasing by nearly 100 percent per year. The magnetic spacing between the heads and media has thus been rapidly deceasing. On the other hand, there is a strong demand for write head costs to be made of materials like CoNiFe alloys that have higher Saturation magnetization than conventional alloys of NiFe. However, these alloys are more easily corroded than NiFe alloy. Hence, a thinner air-bearing surface overcoat is required without sacrificing either the corrosion resistance or the wear durability of GMR heads, so the material used must be denser, harder and provide a higher degree of coverage of the head element's surfaces.
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