Pure Spin Current and Large Inverse Spin Hall Voltages in a Nonconjugated Radical Polymers

Spintronics is emerging as a potentially efficient alternative to traditional electronic devices that use spin rather than electric currents. Despite this, state-of-the-art non-magnetic metals and highly doped conjugated polymers that are critical for spin manipulation suffer from fundamental performance and stability issues when transforming spin currents to transverse electrical currents via Inverse Spin Hall Effect (ISHE). Nonconjugated radical polymers with unpaired electrons offer a unique solution to these challenges owing to their paramagnetic nature and ability to transport pure spin currents by rapid radical-radical exchange interactions with in the material and at device interfaces. Thus, there is a critical need to investigate these class of materials for their spin transport properties in practical device applications. Here, we investigate the spin-transport characteristics of two non-conjugated radical polymers named poly (4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1- oxyl) (PTEO), and poly[3-(4-(1-(3-methoxy-2-methylpropyl)-1<i>H</i>-1,2,3-triazol-4-yl)phenyl)-1,5-dimethyl-1<i>H</i>-1,2λ²,4,5-tetrazin-6(5<i>H</i>)-one], poly(verdazyl ethylene oxide) (PVEO). These polymers show excellent spin-filtering effect leading to giant magnetoresistance(GMR) effect of ~ 80 % in PTEO and ~ 35 % in PVEO at 4 K respectively. This relatively large GMR can be attributed to the radical-radical exchange interactions that promote spin-dependent charge transfer under the presence of external magnetic field. Large room temperature ISHE voltages of 0.10 mV in PTEO and 0.40 mV in PVEO demonstrate their exceptional capability in transporting pure spin currents. These values are comparable to many inorganic semiconductors and higher than many metal-free doped conjugated polymers. Our results demonstrate the first ever application of radical polymers in spintronic devices and thereby paves the way for further development of this field in spintronics community.