Development of current perpendicular to plane differential dual spin valve for ultrahigh resolution

Recently, a differential dual spin valve (DDSV) has been proposed to enhance the downtrack resolution for the application in the hard disk drive recording at 10 Tb/in² and beyond. The following key issues for the implementation of a high-quality DDSV have been addressed. I. Formation of the antiparallel arrangement of the reference magnetization of two spin valves (SVs) with high pinning stability. II. Differential effect of a DDSV. To achieve perfect differential effect in a DDSV, not only should two SVs have the same giant magnetoresistance effect, but their free-layer (FL) magnetization should also respond to a field identically. Using 2.4 nm ruthenium as the gap layer to form a ferromagnetic interlayer coupling between FLs, a good differential effect is achieved. III. Quasistatic characterization of a DDSV. As there is no output from a DDSV under a uniform field, it would be difficult to evaluate performances of a DDSV. By varying the annealing field direction, field response of each SV as well as differential effect can be identified.