Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation The latter arises because the electron transport in π-conjugated

Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the interfaces between the different materials and defects that are common to real devices. Knowledge of these factors is especially important for the relatively new field of organic spintronics, where there is a severe lack of suitable experimental techniques that can yield depth-resolved information about the spin polarization of charge carriers within buried layers of real devices. Here, we present a new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve. The temperature dependence of the measured spin diffusion length is found to be correlated with the device magnetoresistance. 6 The most common method for using the spin in devices is based 7 on the alignment of the electron spin ('up' or 'down') injected electrons from a buried interface in an operational device. 51 Recently it has been shown that it is possible to measure spin 52 injection from an in-plane magnetized ferromagnetic film into a 53 semiconductor 9 , even below the ferromagnetic contacts, using the 54 magneto-optical Kerr effect. This was made possible by carrying out 55 the measurement on a cleaved edge of the sample, but this is not 5