Dual current-perpendicular-to-plane giant magnetoresistive sensors for magnetic recording heads with reduced sensitivity to spin-torque-induced noise

Abstract

Dual IrMn-pinned current-perpendicular-to-plane giant magnetoresistive sensor structures have been investigated, and their signal and noise characteristics are compared to similar standard single sensors, using test structures with sizes down to 50nm. The intrinsic signal ΔRA product is found to be increased by a factor of nearly 2 between single and dual spin valves, although the parasitic resistance due to the second 80-nm-thick IrMn-pinned layer stack limits the net increase in ΔR∕R to a factor of 1.5. For the single spin valve with antiparallel free and reference layers, the noise power spectral density shows a large asymmetry between positive and negative current flows due to strong spin-torque effects for positive (electrons flow from reference layer to free layer) current densities above 1×107A∕cm2. For the dual sensor, however, the critical current density is symmetric in polarity and is increased to above 5×107A∕cm2, resulting in a 5-fold increase in practical sensor output voltage.