A computational investigation of spin filtering at finite temperature in the phenalenyl radical

Creating pure spin current is one of the fundamental goals of spintronics, with many devices utilizing magnetic tunnel junctions and spin valves to create structures which impart a spin polarization onto passing electrons. The use of single molecules to create spin-polarized current is receiving considerable attention in the molecular electronics field, with chiral molecules and radicals emerging as two classes of molecules which can potentially support spin filtering transport behavior. Previous computational studies have shown that derivatives of the radical phenalenyl (PLY) can behave as efficient spin filters, and that this behavior can be tuned by application of bias voltage. However, these studies were performed on minimum-energy structures of Au-PLY-Au single-molecule junctions, and recent publications have shown that the inclusion of temperature-induced motion can lead to conformational changes which can cause drastically different transport behaviors to arise. In this study, we perform ab initio molecular dynamics (AIMD) trajectories in conjunction with the non-equilibrium Green’s function-density functional theory (NEGF-DFT) calculations to calculate the effect finite temperature has on the spin filter efficiency (SFE) of PLY. Over total trajectory lengths of 5 ps, the metal-molecule junction was allowed to evolve at 300, 500, and 700 K, and transport across the system was calculated every 0.1 ps. Surprisingly, the SFE maintained a near-ideal value across all temperatures, although the 700 K trajectory had the most deviations from near-ideal SFE. Through this methodology, we show that PLY behaves as an efficient spin filter at lower temperatures, but that at elevated temperatures the SFE is less robust against temperature-induced conformation changes.