Chiral-induced spin selectivity in polypeptides on Ta/CoFeB/MgO/Ta/Pt thin films exhibiting perpendicular magnetic anisotropy

The chiral-induced spin selectivity (CISS) effect describes multiple phenomena in which an apparent relation exists between the spin orientation of electrons and the chirality of the transport medium [1]. For charge transport studies, this spin selectivity is commonly detected via magnetoresistance measurements. Here, we present a spin valve platform based on a Ta/CoFeB/MgO/Ta/Pt thin film with perpendicular magnetic anisotropy and a coercive field window of 5 – 10 mT. Thiolated 31-monomer polypeptides (C[AAAAK]₆) were deposited as self-assembled monolayers (SAMs). Both atomic force microscopy and X-ray photoelectron spectroscopy indicate the presence of the molecules in a predominantly flat-lying position. Preliminary magnetoelectrical measurements using a modified eutectic gallium-indium top electrode setup suggest the manifestation of magnetoresistance and an apparent spin polarization of ca. 20 %. By varying the thickness of the underlying Pt layer, the spin polarization injected into the chiral SAM can be altered. First results indicate the absence of any significant magnetoresistance at a Pt thickness of ≥ 4 nm, which may be assigned to the strong spin-orbit coupling in Pt, effectively limiting the spin decay length. Overall, the presented architecture could serve as a platform for future studies that evaluate the impact of injected spin polarization and contact potential [2] on the magnitude of the measured CISS effect.

[1] Bloom et al. Chem. Rev. 2024

[2] Tirion and van Wees ACS Nano 2024