Room Temperature Spin Transport through C60 molecules

M. GOBBI; F. GOLMAR; R. LLOPIS; F. CASANOVA; L. HUESO

Donostia

Workshop; Passion for knowledge; 2010

Donostia International Physics Center

Organic semiconductors (OS) have extremely low spin-orbit interaction, so that the main spin scattering mechanism is thought to be the hyperfine coupling with protons [1,2]. Consequently, the electron spin diffusion length is expected to be very long, making OS ideal materials for spintronics. Recently, several experiments have been performed studying the spin injection and transport in organic semiconductors, focusing only on a relatively limited number of molecules [3]. Here, spin transport studies through C60 layers are presented. C60 is commonly used in organic FET and in organic photovoltaics devices, while no spin transport experiments have been carried out with it so far. Nevertheless, it is an ideal molecule to study magnetotransport properties: it does not contain hydrogen atoms, thus minimizing the hyperfine coupling with protons. Hybrid Co/Al2O3/C60/Py vertical spin valves were produced, with the C60 layer thickness ranging between 3 nm and 30 nm, and an Al2O3 layer of around 2 nm between the bottom Co electrode and the C60 layer to improve the effective spin polarization at the interface [4]. AFM and X-ray reflectivity measurements show that C60 grows smoothly on the Al2O3 layer, with roughness below 2 molecular layers. The spin valve resistance-area product is constant for all the junctions grown in the same conditions, and increases exponentially with the C60 thickness. Magnetoresistance has been reproducibly measured at room temperature (see fig.1), suggesting a room temperature spin relaxation length longer than 20 nm. We will compare these results with some of our recent studies in lateral spin valves with C60 channels.