Spin and Charge Injection and Transport in Ferromagnet/Organic Semiconductor/Ferromagnet Heterejunction*

We studied the spin injection and transport in organic semiconductor by employing LSMO and Fe as an anode and cathode in hybrid spin valve structure. Using thin layer ($t$ $<$ 10 nm) of rubrene as a spacer, our device displays MR as high as 50 $\% $ at low temperature and at low bias voltage. The charge injection into organic spacer in our devices is injection limited. At high applied voltage ($V$ $>$ $V_{th}$) field-driven drift current prevails in current density through the organic semiconductor. At low bias $V$, inelastic hopping followed by thermionic emission is dominant at high $T$, which decreases significantly as $T$ lowered. And eventually the current density through the device becomes purely tunneling at low $T$ and $V_b$. The spin and charge injection, effects of inclusion of tunneling barrier, and the effects of crystallinity of organic layer will be discussed.