Effects of oxide seed and cap layers on magnetic properties of a synthetic spin valve

Abstract

A synthetic spin valve comprising Al2O3/Ni–Cr–Fe/Ni–Fe/Pt–Mn/Co–Fe/Ru/Co–Fe/Cu/Co–Fe/Ni–Fe/Cu/Al2O3/Ta films has been annealed and evaluated as a read sensor for ultrahigh-density (⩾20 Gb/in.2) recording. The Al2O3 film used as its oxide seed layer provides an in situ flat surface for the Pt–Mn, Co–Fe and Ni–Fe films to develop strong {111} crystalline textures, thereby increasing its giant magnetoresistance coefficient to as high as 13.8%. Another Al2O3 film used as its oxide cap layer protects the Co–Fe/Ni–Fe sense layers from interface mixing and oxygen interdiffusion, thus improving the soft magnetic properties and thermal stability of the sense layers. Antiferromagnetic/ferromagnetic coupling between the Pt–Mn pinning and Co–Fe/Ru/Co–Fe synthetic pinned layers is strong and thermally stable enough for proper sensor operation. Ferromagnetic/ferromagnetic coupling across the Cu spacer layer is antiparallel, and hence it is feasible to achieve optimal biasing of magnetoresistance responses. This synthetic spin valve is sandwiched into a read gap 0.1 μm in thickness, and is patterned and lapped into a read sensor 0.42 and 0.23 μm in physical width and height, respectively. With a sense current of 4 mA, this read sensor exhibits an effective read width of 0.31 μm, stable magnetoresistance responses, and signal sensitivity of 6.64 mV/μm.