Assessing the Role of Chirality in Magnetic Proximity Effect at Fe-CNTs Interfaces: A First Principle study

This work investigates the role of chirality in the magnetic proximity effect at ferromagnetic-carbon nanotubes (Fe-CNTs) interfaces using first-principles calculations. Motivated by the unresolved microscopic origin of Chirality-Induced Spin Selectivity (CISS), which predicts spin-dependent electron transport in chiral systems, we analyze whether nanotubes chirality significantly affects spin polarization induced by a ferromagnetic iron substrate. Electronic structure calculations were performed within Density Functional Theory (DFT) using periodic SIESTA simulations with the PBE–GGA functional, non-collinear spin–orbit coupling (SOC), and fully relativistic pseudopotentials. Hydrogen-terminated CNTs with different chiralities were placed on an Fe surface, and the interface geometry was optimized to maximize magnetization transfer. Spin polarization was evaluated by computing the difference in the S_z component of carbon atoms between isolated CNTs and Fe–CNT hybrid systems. The results show that, although individual nanotubes exhibit specific variations in their magnetic response, the overall magnetization trend is similar for chiral and achiral structures. If CISS originates purely from structural chirality and SOC, a clear chirality-dependent response should appear already at the equilibrium ground-state DFT level. Since such dependence is not observed, our results constrain theoretical descriptions of CISS, and suggest that additional mechanisms, such as nonequilibrium effects or environmental interactions, may play an essential role in the underlying physics of CISS.