Spin-Torque Noise in CPP-GMR Heads With Current Screen Layer

We investigated the head noise in current perpendicular-to-the-plane giant-magnetoresistive (CPP-GMR) heads with a current screen layer (nano oxide layer having a confined current path) to experimentally evaluate spin-torque noise in the head application. Depending on the direction/magnitude of sensing current, a significant increase in head noise was observed. Some features in noise profiles and a correlation between noise and peak asymmetry are qualitatively reasonable from the perspective of the spin-torque theory. This fact indicates that this extraordinary noise was induced by spin-transfer torque. The spin-torque noise was not observed when the heads were well biased with an orthogonal direction for the free and the reference layer, regardless of whether sensing current was positive or negative. This suggests that the spin-torque noise is not a fatal issue in current screen type CPP-GMR heads with small peak asymmetry.