We report the spin-pump-induced spin transport properties of a pentacene film prepared by thermal evaporation. In a palladium(Pd)/pentacene/Ni 80 Fe 20 tri-layer sample, a pure spin-current is generated in the pentacene layer by the spin-pumping of Ni 80 Fe 20 , which is independent of the conductance mismatch problem in spin injection. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current at room temperature in pentacene films prepared by thermal evaporation.

The spin current relaxation time (τ) in thermally evaporated pentacene films was evaluated with the spin-pump-induced spin transport properties and the charge current transport properties in pentacene films. Under an assumption of a diffusive transport of the spin current in pentacene films, the zero-field mobility and the diffusion constant of holes in pentacene films were experimentally obtained to be ~8.0× 10 -7 m 2 /Vs and ~2.0× 10 -8 m 2 /s, respectively. Using those values and the previously obtained spin diffusion length in pentacene films of 42±10 nm, the τ in pentacene films was estimated to be 150±120 ns at room temperature. This estimated τ in pentacene films is long enough for practical use as a spintronic material.