Spin valves (SVs) are multilayer devices composed of two ferromagnetic
(FM) electrodes separated by a nonmagnetic spacer layer. These devices
exhibit the phenomena of magnetoresistance (MR), that is, a change in electrical
resistance depending on the magnetization direction of the two ferromagnetic
electrodes. Accordingly, they can be used as nonvolatile random-access
memories and magnetic field sensors. The traditional spacer layers in the
SVs are nonmagnetic metal and oxide layer, respectively. More recently
much effort has been devoted to make devices using ƒÎ-conjugated organic
semiconductors (OSEs) as middle spacer in spintronics, owing to the low
cost of processing and their electronic and structural flexibility. Most
importantly, the electron spin diffusion length in OSEs is especially long
because of the weak spin-orbit interaction and weak hyperfine interaction,
making them ideal for spin-polarized electron injection and transport applications.
However, currently, most of the tunneling MR ratio in organic SVs can be observed only at low temperature and quickly disappear or reduce to only several percent at room temperature. This limits its application for the society. Moreover, the physical mechanism of microscopic spin/charge transport in these FM1/OSE/FM2 tri-layer structures, which is paramount to the scientific and technological fusion, remains a challenging issue. In our group, we give our efforts to explore these fundamental puzzles and develop novel organic SV devices. Our investigation will further deepen the understanding of the spin properties of OSEs in organic spintronics and promote the basic research for the final commercial development.