Searching for Cu-X Spacers Using a Half-Metallic Co2FeGa0.5Ge0.5 Electrode to Boost Magnetoresistance in CPP-GMR Devices: A First-Principles Study

Abstract Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices are promising candidates for next-generation hard disk drive (HDD) read heads due to their low resistance-area product (RA) and high-speed operation. This study investigates Cu-based binary alloys (Cu-X) as alternative spacers to conventional Ag spacer in Co2FeGa0.5Ge0.5 (CFGG)-based CPP-GMR devices using first-principles calculations. Majority-spin ballistic conductance, which is essential in the large spin-asymmetry of the interface resistance, was evaluated for CFGG/Cu-X/CFGG(001) trilayers in comparison with CFGG/Ag/CFGG(001) trilayer. The results show that several spacer materials have possibilities to enhance the MR ratio compared to Ag. In particular, we found that B2-CuZn will be the most suitable for CFGG electrode. The large majority-spin conductance of CFGG/CuZn/CFGG(001) is attributed to p-d hybridization between CFGG and Cu s-states near the Γ point, which enhances electron transport efficiency, while the thermal stability of the interface spin-moment at CFGG/CuZn(001) is slightly smaller than that of CFGG/Ag(001). Finally, we proposed that the insertion of Ag layer between the CFGG and CuZn interfaces will enhance not only the spin-asymmetry in the interface resistance but also the thermal stability of the interface spin-moment.