Recently, the team of Professor Zhao Qiang and Associate Professor Luo Zhongzhong from the College of Electronic and Optical Engineering & College of flexible electronic (future technology) of Nanjing University of Posts and Telecommunications made new progress in the field of organic spintronic devices, and revealed the key role of molecular packing on interface spin polarization. On April 5th, the related achievements were published in the international academic journal Science Advances with the title of “Revealing the key role of molecular packing on interface spin polarization at two-dimensional limit in spintronic devices”. Professor Zhao Qiang, Associate Professor Luo Zhongzhong and Professor Qin Wei from School of Physics of Shandong University are co-authors, and Associate Professor Luo Zhongzhong and Researcher Song Xiangxiang from Suzhou Institute for Advanced Research of University of Science and Technology of China are the co-first author of the paper.
Due to the advantages of weak spin-orbit coupling and hyperfine interaction, organic materials are promising for spintronic applications. A variety of devices have been demonstrated including spin valves, spin memory devices and light-emitting diodes. It is expected that the spinterfaces between organic semiconductors and ferromagnetic (FM) metals, which are sensitive to structural properties and side chain substitution of the molecules, play an important role in these spintronic devices. However, there are still several obstacles lying ahead for fully understanding these molecular spinterfaces from the experimental point of view, thus limiting the device applications based on organic materials. First, organic semiconductors with high mobility and low density of disorders/traps are rarely implemented, preventing further fabrication of high-quality interfaces. Second, evaporation of FM metals on organic semiconductors usually damages the adjacent molecular layers, leading to degraded quality of the interface. These challenges make researchers investigate spinterfaces by absorbing organic molecules on FM metals alternatively, instead of studying them from the device perspective.
Aiming at this key scientific problem, the team combined high-quality two-dimensional layered molecular crystals and solvent-free van der Waals magnetic-electrode integration technology to realize atomically-smooth ferromagnetic metal/molecule interfaces. Employing such high-quality interfaces, the researchers investigated spin injection of spin valve devices based on organic films of different layers, in which molecules are packed in different manners. And the researchers further found the measured magnetoresistance and estimated spin polarization increase dramatically for bilayer devices, compared with their monolayer counterparts. Such observations reveal the key role of molecular packing on spin polarization, which is supported by density functional theory calculations. This research work provides new routes towards designing spinterfaces for organic spintronic devices.
This work is supported by the National Natural Science Foundation of China, the Natural Science Foundation of Jiangsu Province, Natural Science Foundation of the Higher Education Institutions of Jiangsu Province, the State Key Laboratory of Organic Electronics and Information Display and Guangdong Province Research and Development in Key Fields from Guangdong Greater Bay Area Institute of Integrated Circuit and System.
Organic spintronic devices with atomically-smooth interfaces reveal thekey role of molecular packing on interface spin polarization at two-dimensional limit
（Writer: Luo Zhongzhong Preliminary Reviewer: Zhao Qiang, Cheng Yong Editor: Wang Cunhong Final Reviewer: Zhang Feng）