  We have experimentally tested the hypothesis of free charge carrier mediated
spin-transport in the small molecule organic semiconductor Alq3 at room
temperature. A spin current was pumped into this material by pulsed
ferromagnetic resonance of an adjacent NiFe layer, while a charge current
resulting from this spin current via the inverse spin-Hall effect (ISHE) was
detected in a Pt layer adjacent on the other side of the Alq3 layer, confirming
a pure spin current through the Alq3 layer. Charge carrier spin states in Alq3,
were then randomized by simultaneous application of electron paramagnetic
resonance (EPR). No influence of the EPR excitation on the ISHE current was
found, implying that spin-transport is not mediated by free charge-carriers in
Alq3.
