Exchange coupling of sputter deposited NiCo-O/NiFe thin films

NiCo-O serving as the exchange layer in a spin valve structure has the advantage of being corrosion resistant and unable to shunt sensing current in the read element. In this work, NiCo-O/NiFe thin films are studied. The films are deposited on Si wafers using rf sputtering. The antiferromagnetic NiCo-O films were reactively sputtered from alloy targets; one has a 55 at.% of Co and the other 60 at.% of Co. The chamber atmosphere is an Ar/O-2 mixture containing similar to 10% O-2. For films with optimal structures, the exchange strength is around 40-45 Oe. The coercivity of the pinned layer is between 18-26 Oe. The exchange strength and coercivity as a function of NiCo-O thickness (with NiFe thickness fixed at 200 Angstrom) and NiFe thickness (with NiCo-O fixed at 250 Angstrom) are examined. The exchange field is found to increase with the antiferromagnet thickness initially and then flatten out or drop slightly when the antiferromagnet thickness is beyond 200-250 Angstrom. Blocking temperature of the bilayer films is also measured and is found to increase with NiCo-O thickness. NiCo-O with lower Co content shows slightly higher blocking temperature. (C) 1996 American Institute of Physics.