We report room-temperature measurements of the spin-relaxation times T1 and T2 of electron-hole chargecarrier
spins in an organic light-emitting diode based on the π-conjugated polymer SY-PPV at low (1mT �
B0 � 10mT) static magnetic fields, using electrically detected—through spin-Rabi oscillation-controlled recombination
currents—magnetic resonant Hahn-echo and inversion-recovery pulse sequences. When random local
hyperfine fields and external magnetic fields compete in magnitude, charge carrier spin-quantization axes are no
longer well defined, and striking magnetic-field dependencies of spin-lattice relaxation times are found, while
spin coherence times remain mostly field-independent. These results corroborate the magnetic-field sensitivities
of observables governed by radical-pair physics.