Presentation Information
[11a-E208-10]High throughput exploration of Ni-Al spacer composition enhancing magnetoresistance (MR) properties in CPP-GMR devices with half metallic Heusler alloy electrodes
〇(D)MdSarwar Pervez1,2, Vineet Barwal2, Hirofumi Suto2, Suwannharn Nattamon2, Kodchakorn Simalaotao2, Taisuke Sasaki2, Yuya Sakuraba1,2 (1.Tsukuba Univ., 2.NIMS)
Keywords:
CPP-GMR,Heusler alloy,Spacer materials
Achieving a high magnetoresistance (MR) ratio in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices remains a critical challenge for next-generation hard disk drive (HDD) technologies with areal densities beyond 2 Tb/in². CPP-GMR devices are attractive for such applications because of their inherently low resistance–area (RA) product compared with tunnel magnetoresistance (TMR) devices. In this study, we investigate the effect of Ni–Al spacer composition on spin-dependent transport in CPP-GMR devices employing Co-based Heusler alloy Co2Mn0.65Fe0.35Ge (CMFG) electrodes.
CPP-GMR devices with composition-spread NixAl1-x (0.3 ≤ x ≤ 0.7) spacer layers (3 and 5 nm) were fabricated using a high-throughput combinatorial sputtering system, Fig. 1(a). Fully epitaxial growth was confirmed by X-ray diffraction, while L21 ordering of CMFG electrodes and B2 ordering of the NiAl spacer were verified by transmission electron microscopy (TEM) after annealing at 250 °C and 350 °C. A strong dependence of the MR ratio on spacer composition was observed, Fig. 1(b), with a maximum MR ratio of 15.8% achieved in 3 nm spacer devices annealed at 250 °C with Ni45Al55 composition, which is among the highest MR ratios reported for NiAl-based CPP-GMR systems [1].
Increasing the annealing temperature above 250 °C degraded MR performance due to interfacial roughness and Co interdiffusion, as confirmed by TEM. Furthermore, comparison of devices with 3 and 5 nm NiAl spacers enabled evaluation of the spin diffusion length, which decreased significantly in the Al-rich composition range (Al > 50 at. %), potentially due to increased defect scattering associated with Ni vacancy formation, consistent with temperature-dependent resistivity measurements (10–300 K) and previous theoretical studies [2].
CPP-GMR devices with composition-spread NixAl1-x (0.3 ≤ x ≤ 0.7) spacer layers (3 and 5 nm) were fabricated using a high-throughput combinatorial sputtering system, Fig. 1(a). Fully epitaxial growth was confirmed by X-ray diffraction, while L21 ordering of CMFG electrodes and B2 ordering of the NiAl spacer were verified by transmission electron microscopy (TEM) after annealing at 250 °C and 350 °C. A strong dependence of the MR ratio on spacer composition was observed, Fig. 1(b), with a maximum MR ratio of 15.8% achieved in 3 nm spacer devices annealed at 250 °C with Ni45Al55 composition, which is among the highest MR ratios reported for NiAl-based CPP-GMR systems [1].
Increasing the annealing temperature above 250 °C degraded MR performance due to interfacial roughness and Co interdiffusion, as confirmed by TEM. Furthermore, comparison of devices with 3 and 5 nm NiAl spacers enabled evaluation of the spin diffusion length, which decreased significantly in the Al-rich composition range (Al > 50 at. %), potentially due to increased defect scattering associated with Ni vacancy formation, consistent with temperature-dependent resistivity measurements (10–300 K) and previous theoretical studies [2].