Effect of Current-Confined Path on Spin-Torque Noise in CPP-GMR Heads With Current Screen Layer

We investigated the effect of current-confined path on spin-torque noise in current perpendicular to the plane giant magnetoresistive (CPP-GMR) heads with a current screen layer (a nano-oxide layer having current-confined paths). We found that both in measurement and calculation spin-torque noise of heads with a resistance area (RA) product of 1.0 Omega middot mum² was smaller than that with RA of 0.25 Omega middot mum². We also found that the calculated spin-torque noise decreased as the exchange stiffness constant in the free layer increased. These behaviors indicate that the magnetization fluctuation in conductive areas can be reduced by the magnetic coupling with the magnetization in nonconductive areas. Accordingly, the current screen structure is effective in suppressing the spin-torque noise. To reduce spin-torque noise in CPP-GMR heads with a current screen layer, it is effective to reduce the area of each metallic nano-hole while keeping the total conductive area constant since the magnetic coupling between the magnetization in conductive and nonconductive areas keeps strong.