Exchange-Dominated Pure Spin Current Transport in Alq3 Molecules

We address the controversy over the spin transport mechanism in Alq(3) utilizing spin pumping in the Y3Fe5O12/Alq(3)/Pd system. An unusual angular dependence of the inverse spin Hall effect is found. It, however, disappears when the microwave magnetic field is fully in the sample plane, excluding the presence of the Hanle effect. Together with the quantitative temperature-dependent measurements, these results provide compelling evidence that the pure spin current transport in Alq(3) is dominated by the exchange-mediated mechanism.