Tunnel-valve and spin-valve structures with in situ in-stack bias

Abstract

As recording densities increase above 100 Gbit/in2, read sensor trackwidth must be reduced below 0.2 μm. To improve sensor operation, it is necessary to develop alternatives to traditional contiguous junction hard bias stabilization schemes. One such alternative consists of an in-stack magnetic bias layer deposited in close proximity to the sensor layer. Upon trackwidth definition, this results in a magnetostatic bias coupling at the sensor edges. For in-stack bias to be effective, several aspects must be optimized. (1) The bias layer must be as close as possible to the sensor free layer to increase the biasing effect. (2) Any direct ferromagnetic coupling between free and bias layer across a spacer layer must be minimized. (3) The bias layer must be well pinned and oriented perpendicular to the tunnel-valve pinned layer. To achieve these goals, we have studied bottom-PtMn spin-valve and tunnel valve structures of the type Ta/PtMn/CoFe/(Al2O3 or Cu)/CoFe/NiFe/Ta/CoFe/IrMn/Ta deposited in situ in a single process by magnetron sputtering. Ta thicknesses between 10 and 30 Å have been used to decouple the bias layer from the free layer, and IrMn is used to pin the bias layer magnetization.