Chirality-induced spin selectivity in organic spin valves utilizing 1,1′-Bi-2-naphthol with and without AlOx insulating layers

Recently, chirality-induced spin selectivity (CISS) has been observed in chiral molecules and has become attractive for applications in magnetoresistance (MR) devices. In this study, we fabricate CISS-based organic spin valves (OSVs) consisting of the chiral molecule 1,1′-Bi-2-naphthol (BINOL), sandwiched between an Au electrode and Co/Pt layers with perpendicular magnetic anisotropy, with and without an AlOx layer. We successfully fabricated Au/R-(+)-BINOL/Co/Pt/Co/Pt/Cr (Au/R-(+)-BINOL/[Co/Pt]2) and Au/S-(−)-BINOL/[Co/Pt]2 OSVs. These devices, which exhibit sharp interfaces, demonstrate clear CISS-based MR effects under a low magnetic field of ∼20 mT at room temperature. The MR curves of both Au/R-(+)-BINOL/[Co/Pt]2 and Au/S-(−)-BINOL/[Co/Pt]2 OSVs correspond well to the perpendicular magnetization curves of the [Co/Pt]2 electrodes. The polarity of the resistance change also exhibits opposite behaviors in the two devices. This indicates that an MR effect based on CISS is successfully observed in the Au/BINOL/[Co/Pt]2 OSVs. In addition, we fabricate Au/BINOL/AlOx/[Co/Pt]2 OSVs, in which an AlOx layer is inserted. We find that inserting an AlOx layer at the molecule/Co interface decreases both the MR and signal-to-noise (S/N) ratios of the MR curves compared with those of devices without an AlOx layer. The results of this study can contribute to elucidating the mechanism of CISS and provide new insights into its effect for spintronic device applications.