Magnetoresistance effect in rubrene-based spin valves at room temperature

Spin Selectivity in Chiral Hybrid Cobalt Halide Films with Ultrasmooth Surface

Introducing chirality into low-dimensional hybrid organic-inorganic halides (HOIHs) creates brand-new opportunities for HOIHs in spintronics and spin-related optoelectronics owing to chirality-induced spin selectivity (CISS). However, preparing smooth films of low-dimensional HOIHs with small roughness is still a great challenge due to the hybrid and complex crystal structure, which severely inhibits their applications in spintronic devices. Exploring new lead-free chiral HOIHs with both efficient spin selectivity and excellent film quality is urgently desired. Here, cobalt-based chiral metal halide crystals (R/S-NEA)₂ CoCl₄ constructed by 0D [CoCl₄ ] tetrahedrons and 1-(1-naphtyl)ethylamine (NEA) are synthesized. The orderly configuration of NEA molecules stabilized by noncovalent CH···π interaction endows (NEA)₂ CoCl₄ with good film-forming ability. (NEA)₂ CoCl₄ films exhibit strong chiroptical activity (g_CD  ≈ 0.05) and significant spin-polarized transport (CISS efficiency up to 90%). Furthermore, ultrasmooth films (roughness ∼ 0.3 nm) with enhanced crystallinity can be achieved by incorporating tiny amount tris(8-oxoquinoline)aluminum that has analogous conjugated structure to NEA. The realization of highly efficient spin selectivity and sub-nanometer roughness in lead-free chiral halides can boost the practical process of low-dimensional HOIHs in spintronics and other fields.

Comparisons of magnetic defects and coercive forces for Co/Si(100) and Co/rubrene/Si(100)

Spintronics can add new functionalities to electronic devices by utilizing the spin degree of freedom of electrons. Investigating magnetic defects is crucial for the performance of spintronics devices. However, the effects of magnetic defects that are introduced by the presence of organic materials on their magnetic properties remain unclear. Herein, we report on a novel method using rubrene combined with Kerr microscopy that enables quantitative and direct measurements of magnetic defect density. For Co/Si(100) at a magnetic field near the coercivity value, Kerr microscopy images show a dark image with some magnetic defects. Because of domain wall motion, small patches gradually change the contrast. These magnetic defects are immovable at different magnetic fields and serve as pinning sites for domain wall motion. Experimental evidence shows that coercive force can be reduced by controlling the magnetic defect density by introducing small amounts of rubrene into the films. Furthermore, direct quantitative measurements of magnetic defects show both a one-dimensional bowing of domain walls and strong defect-domain wall interactions in the films. Based on these findings, we propose a viable strategy for reducing the coercive force of Co/Si(100) by controlling the magnetic defect density and this new information promises to be valuable for future applications of spintronics devices.

Interface hybridization and spin filter effect in metal-free phthalocyanine spin valves

Spin–orbit coupling has been regarded as the core interaction to determine the efficiency of spin conserved transport in semiconductor spintronics. Here, we show the spin filter effect should be responsible for the magnetoresistance of H₂Pc device.

Tuning Charge Carrier and Spin Transport Properties via Structural Modification of Polymer Semiconductors

Targeted design of organic semiconductors in organic spintronics is relatively limited. Therefore, four conjugated polymers with analogous structures based on isoindigo (IID) units were designed and synthesized to investigate the structure-property relationships in spin and charge carrier transport. Structural design strategies include introduction of pyridinic nitrogen atoms into IID units to change electronic structures and alteration of different branching points of alkyl chains to adjust the aggregation structure. By fabricating polymer field-effect transistors (PFETs) and organic spin valves (OSVs), all of the polymers exhibited good ambipolar field-effect properties (all of the mobilities exceeding 0.3 cm² V^-1 s^-1) and relatively high magnetoresistance (MR) values (maximum up to 25%). Most importantly, it is found that the introduction of pyridinic nitrogen into the IID units can improve MR values of OSVs and electron mobilities of PFETs, whereas the extension of alkyl chain branching points can reduce MR values of the conjugated polymers. This work is the first attempt to thoroughly study the structure-property relationship in the OSVs, combined with molecular design of the conjugated polymers, which provides a guideline for molecular engineering, especially for organic spintronics.

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.

Orbital Redistribution Enhanced Perpendicular Magnetic Anisotropy of CoFe3N Nitrides by Adsorbing Organic Molecules

Organic/ferromagnetic spinterface plays a significant role in organic spintronics and the manipulation of spinterface will help to optimize the performance of molecular devices. Here, we systematically investigate how the magnetic anisotropy can be tailed by adsorbing different organic molecules on CoFe₃N surface. It is found that the adsorption of C₆H₆, C₆F₆, and SC₄H₄ molecules on the FeCo-hollow site enhances the perpendicular magnetic anisotropy (PMA) of CoFe₃N. The redistribution of Fe/Co d-orbitals near the Fermi level has an important effect on the modulation of PMA. Asymmetric SC₄H₄ adsorbed system has a larger PMA than symmetric C₆H₆ and its halide due to the hybridization between S p _z and Fe d _z² orbitals instead of C atom. Our results indicate that appropriate organic molecule adsorption can improve the magnetic properties of ferromagnets, which benefits organic spintronic devices.

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.