High-output current-perpendicular to the plane giant magnetoresistance sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents

Abstract

It is shown that the maximum stable output of a current-perpendicular to the plane giant magnetoresistance sensor is increased significantly by using a synthetic-ferrimagnet free layer, provided the electron current flows from free layer to reference layer. This free layer allows a larger magnetoresistance ratio for a given free layer magnetic moment, and in addition results in a greater than threefold increase in the critical current, above which spin-torque instability of the free layer occurs. In read heads with net free layer moments equivalent to only 4.5 nm of Ni80Fe20, this effect is shown to result in sustainable sense current densities above 2×108 A/cm2.