Polycrystalline CPP-GMR devices using <001> textured Co<inf>2</inf>Fe(Ga<inf>0.5</inf>Ge<inf>0.5</inf>) Heusler alloy layer and conductive Mg<inf>0.5</inf>Ti<inf>0.5</inf>O<inf>x</inf> buffer layer

Abstract

Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with Co-based Heusler alloys have recently drawn considerable attention due to their potential application as read sensors for ultrahigh density magnetic recording.1,2,3,4 With a non-magnetic Ag spacer layer, the resistance change-area product (ΔRA) of epitaxial pseudo spin valves (PSVs) on single crystalline (001) MgO substrates has exceeded 10 mΩ μm2 by using quaternary ferromagnetic (FM) Heusler alloys such as Co 2 Fe(Ga 0.5 Ge 0.5 ) (CFGG) and Co 2 Fe 0.4 Mn 0.6 Si (CFMS). From a practical point of view, however, we need to develop CPP-GMR sensors with polycrystalline thin films at relatively low annealing temperatures ( textured polycrystalline CPP-GMR using MgO buffer layer showed favorable device thermal stability and moderate ΔRA of 5.8 mΩ μm2 at 400°C was obtained. Nevertheless, it is not industrially viable because MgO as an insulator cannot be used for the fabrication of the actual CPP-GMR sensors. In this work, we report the CPP-GMR properties and microstructure of PSV devices using textured FM Heusler layer CFGG and Ag spacer with a conductive buffer layer Mg 0.5 Ti 0.5 O x (MTO)6 deposited on an chemically-mechanically polished (CMP) Ta/Cu/Ta electrode on thermally oxidized Si substrates. Relatively large ΔRA of 6.6 mΩ μm2 and desirable interfacial smoothness make it a promising candidate for actual read head design.