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Magnetoresistance (MR) refers to the change in resistivity of materials in the presence of a magnetic field. The measure of this change in resistivity is expressed as D R/R. The greater the D R/R ratio, the more sensitive/accurate the Thin Film Head (TFH) will be. Permalloy (Ni/Fe) is known as one of the most effective Magnetoresistive materials.
In Giant Magnetoresistive (GMR) technology, the measure of the change in resistivity, D R/R, is magnified. Two magnetic layers sandwich a conductive layer, usually Copper. One magnetic layer is “magnetically” pinned in place while the other is “free”. The result is that the original MR (D R/R) remains, but has enhanced sensitivity due to magnetic directions.
Williams Products Used – PureCON™, ME™
As Magnetoresistive (MR) heads developed, new alloys of magnetic materials were required. Typical (MR) materials are Ni/Fe(permalloy), Ta, Cu, Au, NiFeX, Al(2)O(3), Cr, CoPt and CoCrPt.
Typical (GMR) materials are: NiFe, NiFeCo, CoFe, Co, Cu, Ta, Ti, Zr, Au, Ru, Cr, CoPt, CoCrPt, Al(2)O(3), SiO(2), FeNi, FeTa, FeTaCr, FeAl, FeZr, NiFeCr, NiFeX.
The introduction of an antiferromagnetic material, to “pin” one of the two magnetic layers, is required for GMR or spin valve technology. Some examples of antiferromagnetic materials are, FeMn, MnNi, MnPt, MnIr, and MnPdPt.
What makes GMR Heads unique?
GMR technology takes MR one step further by adding a second film to the read element. These two films work with or against each other, depending on certain conditions. Working with each other creates low resistance while working against each other creates high resistance. The GMR sensor does this via what is termed “spin valve” technology. The introduction of an antiferromagnetic material, to “pin” one of the two magnetic layers, is required for GMR or spin valve technology.
Schematic Diagram - GMR Structure
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