High-output CPP-GMR sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents

TL;DR

This paper demonstrates that using a synthetic ferrimagnet free layer in CPP-GMR sensors significantly enhances maximum output stability and critical current, enabling higher sense current densities for improved sensor performance.

Contribution

The study introduces a synthetic ferrimagnet free layer design that increases stable output and critical current in CPP-GMR sensors, surpassing previous limitations.

Findings

Maximum stable output is significantly increased.

Critical current for spin-torque instability is tripled.

Sense current densities above 2×10^8 A/cm² are achievable.

Abstract

It is shown that the maximum stable output of a CPP-GMR 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 three-fold 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 4.5nm of Ni80Fe20, this effect is shown to result in sustainable sense current densities above 2e8 A/cm2.