Polycrystalline CPP-GMR devices using <001> textured Co₂Fe(Ga_0.5Ge_0.5) Heusler alloy layer and conductive Mg_0.5Ti_0.5O_x buffer layer

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 Co₂Fe(Ga_0.5Ge_0.5) (CFGG) and Co₂Fe_0.4Mn_0.6Si (CFMS). From a practical point of view, however, we need to develop CPP-GMR sensors with polycrystalline thin films at relatively low annealing temperatures (<400°C). Our previous work on <001> 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 <001> textured FM Heusler layer CFGG and Ag spacer with a conductive buffer layer Mg_0.5Ti_0.5O_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.