Measuring charge carrier spin relaxation times in a π-conjugated polymer using pulsed electrically detected magnetic resonance in absence of magnetic polarization*

We report measurements of the spin relaxation times T₁ and T₂ of charge carrier spin states in the π-conjugated polymer SY-PPV at room temperature under low static magnetic field conditions (1mT ≤ B₀ ≤ 4mT), in near absence of spin polarization, using a pulsed electrically detected magnetic resonance (pEDMR) scheme, where spin-permutation symmetry dependent charge carrier recombination currents are detected after short, coherent (pulsed) Hahn-echo and inversion recovery pulse trains [1] are applied to organic light emitting diodes (OLED) devices. As we performed these measurements at B₀ ∼ the oscillating magnetic resonant driving field B₁ [2, 3], these experiments required arbitrary waveform generation (AWG) for the direct synthesis of the coherent RF-pulse sequences. Since B₀ was also similar to hydrogen induced random local hyperfine fields in our experiments, we could observe changes of T₁ with small changes of B₀, causing a magnetic field dependence of the spin-dependent electric device current. [1] W. J. Baker et al., Phys. Rev. Lett. 108, 267601 (2012). [2] D. P. Waters et al., Nature Physics 11, 910 (2015). [3] L. Dreher et al., Phys. Rev. B 91,075314 (2015).