Spintronic study based on molecular spin valves

Abstract

Because of their extremely weak spin-orbit coupling and hence very long spin relaxation time, molecular semiconductors have considered to be very promising materials in spintronics. Since the first observation of spin transport in molecular semiconductors in 2002, molecular spintronics, as an emerging subject for studying spin-correlated phenomenon of electrons in molecular matrix, has attracted considerable research interests in the previous decade. Molecular spin valve is the most prototypical device in molecular spintronic, which should be the best test bed to study spintronic processes in molecules, including spin injection, spinterfacial effect, spin transport, as well as novel spintronic functions. Thus, to achieve highly reproducible molecular spin valves with high performances is of significant importance to the field of molecular spintronics, in which the efficient spin injection-transport process is the necessary precondition. However, according to current studies, there are several unexpected challenges for enhancing spin injection in spin valves, such as top electrode diffusion into molecular layer during device fabrication and the bad energy level alignment between ferromagnetic electrodes and molecules. To get away from these problems and improve device performance, considerable contributions have already been made to enhance spin injection from perspective of creating novel fabrication methods, optimizing device structure as well as various interfacial engineering methods. Besides, the spinterfacial effects at the interface between ferromagnetic electrodes and molecules are also considered to be crucial for spin injection. In latest studies, hybridized interface state (HIS) was proposed to characterize interaction between ferromagnetic electrode and the first molecular layer, and its spin-density of state at Fermi level of ferromagnetic electrode was changed. Therefore, spin polarization was influenced; as well its electronic structure at HIS was rebuilt to affect spin injection. In this review, research advances regarding spin transport mechanisms are also summarized, including tunneling transport and hopping transport separately. According to few recent reports, it is found that the hopping spin transport mode may avail longer spin transport distance especially at room temperature. Moreover, functional spintronic devices, integrated the spin transport and molecular functions (such as optical, electrical or spinterfacial) in one chip, are briefly introduced, which attracted considerable research interest very recently due to the great potential for applications in future. To summarize, the plentiful contributions regarding spintronic device, including performance optimization as well as mechanism study, have greatly facilitated the development of molecular spintronics in the past decade. However, molecular spintronics is an interdisciplinary filed of chemistry, physics and materials, thus exploring novel molecules that are suitable for spintronic applications must be one of the most important issues in future development of molecular spintronics.