Spin Response in Organic Spin-Valves based on LSMO Electrodes*

We fabricated spin-valves made of organic semiconductor (OSEC) thin films sandwiched between ferromagnetic La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO) and cobalt electrodes, using several OSEC small molecules. We measured the temperature (T) and voltage bias (V) dependence of the spin-valve related giant magneto-resistance (GMR) effect. We found a universal GMR decrease with T, where the GMR completely diminishes at $\sim $ 250K regardless of the OSEC layer. We show evidence that the underlying mechanism for the GMR decrease with T is the decrease in the spin injection capability of the LSMO electrode. We also found that the GMR steeply decreases with V, and is asymmetric respect to the applied voltage direction.