Giant Magnetoresistance and Inverse Spin Hall Effect in Non-Conjugated Radical Polymers

Non-conjugated radical polymers offer new opportunities for the development of emerging technologies that utilize the spin-degree of freedom. Their light-element composition, weak spin orbit coupling, synthetic modularity,and high chemical stability offer attributes that are unavailable from other semiconducting materials. However, developing an understanding of how electronic structure correlates with emerging transport phenomena remains central to their applications. Amidst the significant focus on unraveling the magnetic properties of these materials, the intricate interplay between radicals and spin-dependent transport phenomena in these materials remain significantly underexplored. Thus, there is a critical need to discover new classes of materials that could provide effective means of transporting pure spin currents. 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)-1H-1,2,3-triazol-4-yl)phenyl)-1,5-dimethyl-1H-1,2λ²,4,5-tetrazin-6(5H)-one], poly(verdazyl ethylene oxide) (PVEO). Owing to their intricate molecular structure, both polymers exhibit excellent spin-filtering properties that manifests as giant magnetoresistance effect (~ 80 %) in PTEO and ~ 35 % in PVEO at 4 K. This effect can be attributed to the effective radical-radical interactions that promote spin-dependent charge transfer under the presence of external magnetic field. Moreover, we utilized both polymers in trilayer spin pumping device architectures (Ferromagnet/Polymer/ Pd), and evaluated their performance in propagating pure spin currents. Large room temperature inverse spin hall effect voltages are observed in both polymers with (~ 0.10 mV) in PTEO and (~ 0.40 mV) in PVEO. These values are comparable to many inorganic semiconductors and higher than many metal-free conventional organic semiconductors studied to date. Specifically, our effort demonstrates the coupled materials and device characterizations that are necessary to establish the fundamental structure-function design rules of this underexplored class of materials and thereby paves the way for radical polymer based spintronic applications.