Oxygen Impurities Link Bistability and Magnetoresistance in Organic Spin Valves

Strain-restricted transfer of ferromagnetic electrodes for constructing reproducibly superior-quality spintronic devices

Spintronic device is the fundamental platform for spin-related academic and practical studies. However, conventional techniques with energetic deposition or boorish transfer of ferromagnetic metal inevitably introduce uncontrollable damage and undesired contamination in various spin-transport-channel materials, leading to partially attenuated and widely distributed spintronic device performances. These issues will eventually confuse the conclusions of academic studies and limit the practical applications of spintronics. Here we propose a polymer-assistant strain-restricted transfer technique that allows perfectly transferring the pre-patterned ferromagnetic electrodes onto channel materials without any damage and change on the properties of magnetism, interface, and channel. This technique is found productive for pursuing superior-quality spintronic devices with high controllability and reproducibility. It can also apply to various-kind (organic, inorganic, organic-inorganic hybrid, or carbon-based) and diverse-morphology (smooth, rough, even discontinuous) channel materials. This technique can be very useful for reliable device construction and will facilitate the technological transition of spintronic study.

Visualizing electroluminescence process in light-emitting electrochemical cells

Electroluminescence occurs via recombination reactions between electrons and holes, but these processes have not been directly evaluated. Here, we explore the operation dynamics of ionic liquid-based light-emitting electrochemical cells (LECs) with stable electroluminescence by multi-timescale spectroscopic measurements synchronized with the device operation. Bias-modulation spectroscopy, measuring spectral responses to modulated biases, reveals the bias-dependent behavior of p-doped layers varying from growth to saturation and to recession. The operation dynamics of the LEC is directly visualized by time-resolved bias-modulation spectra, revealing the following findings. Electron injection occurs more slowly than hole injection, causing delay of electroluminescence with respect to the p-doping. N-doping proceeds as the well-grown p-doped layer recedes, which occur while the electroluminescence intensity remains constant. With the growth of n-doped layer, hole injection is reduced due to charge balance, leading to hole-accumulation on the anode, after which LEC operation reaches equilibrium. These spectroscopic techniques are widely applicable to explore the dynamics of electroluminescence-devices.

Spin Injection and Transport in Organic Materials

This review introduces some important spin phenomena of organic molecules and solids and their devices: Organic spin injection and transport, organic spin valves, organic magnetic field effects, organic excited ferromagnetism, organic spin currents, etc. We summarize the experimental and theoretical progress of organic spintronics in recent years and give prospects.

Spin Transport in Organic Molecules

Because of the considerable advantages of functional molecules as well as supramolecules, such as the low cost, light weight, flexibility, and large area preparation via the solution method, molecular electronics has grown into an active and rapidly developing research field over the past few decades. Beyond those well-known advantages, a very long spin relaxation time of π-conjugated molecules, due to the weak spin-orbit coupling, facilitates a pioneering but fast-growing research field, known as molecular spintronics. Recently, a series of sustained progresses have been achieved with various π-conjugated molecular matrixes where spin transport is undoubtedly an important point for the spin physical process and multifunctional applications. Currently, most studies on spin transport are carried out with a molecule-based spin valve, which shows a typical geometry with a thin-film molecular layer sandwiched between two ferromagnetic electrodes. In such a device, the spin transport process has been demonstrated to have a close correlation with spin relaxation time and charge carrier mobility of π-conjugated molecules. In this review, the recent advances of spin transport in these two aspects have been systematically summarized. Particularly, spin transport in π-conjugated molecular materials, considered as promising for spintronics development, have also been highlighted, including molecular single crystal, cocrystal, solid solution as well as other highly ordered supramolecular structures.

Controlling Magnetoresistance by Oxygen Impurities in Mq3-Based Molecular Spin Valves

The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. Although carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of the charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical importance of the carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSV response.

Magnetoresistance Effect and the Applications for Organic Spin Valves Using Molecular Spacers

Organic spin devices utilizing the properties of both spin and charge inherent in electrons have attracted extensive research interest in the field of future electronic device development. In the last decade, magnetoresistance effects, including giant magetoresistance and tunneling magnetoresistance, have been observed in organic spintronics. Significant progress has been made in understanding spin-dependent transport phenomena, such as spin injection or tunneling, manipulation, and detection in organic spintronics. However, to date, materials that are effective for preparing organic spin devices for commercial applications are still lacking. In this report, we introduce basic knowledge of the fabrication and evaluation of organic spin devices, and review some remarkable applications for organic spin valves using molecular spacers. The current bottlenecks that hinder further enhancement for the performance of organic spin devices is also discussed. This report presents some research ideas for designing organic spin devices operated at room temperature.