Evidence of pure spin-current and first organic Spin-Valve based on non-conjugated radical polymer glass

Organic radicals with unpaired electrons have attracted burgeoning attention due to their intriguing technological applications in organic electronics, organic radical batteries, optoelectronics, electrochemical systems, and organic spintronic and magnetic devices. While significant efforts have developed magnetic and spin-correlated electronic properties, evaluating the subtle interplay with spins and spin-dependent transport in these materials is barely explored. The effect of external magnetic field on device resistance (i.e,, magnetoresistance) is one such property that aims at explaining how radical spin couples with externally applied magnetic and electric fields, however it is only limited to closed-shell conjugated polymers and single-molecule based radical junctions. Thus, there is a critical need to discover new classes of materials that could provide coexisting system of intrinsic electrical conductivity and magnetism favorable for spintronic applications. Here we show that poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1- oxyl) (PTEO), a non-conjugated radical polymer, exhibits excellent spin-filtering property upon annealing above its glass transition temperature that manifests as giant magnetoresistance effect (~ 80 %) at T = 4.2 K. As the temperature is increased, the magnitude of magnetoresistance decreases and (~ 5 %) is observed at T = 30 K. The observed giant magnetoresistance effect is attributed to increased intermolecular spin-spin interactions upon annealing that promotes spin-aligned transport. Moreover, we employ ferromagnetic resonance spin pumping in a ferromagnet/ PTEO/ non-magnetic spin-sink trilayer to demonstrate the importance of PTEO in carrying pure spin-current that results in large inverse spin hall effect (ISHE) voltages that is difficult to achieve with organic systems. 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.