Protonation control of spin transport properties in magnetic single-molecule junctions
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Protonation control of spin transport properties in magnetic single-molecule junctions Shuai Qiu1, Yuan-Yuan Miao1, Guang-Ping Zhang1, Jun-Feng Ren1, Chuan-Kui Wang1,*, and Gui-Chao Hu1,* 1
Shandong Key Laboratory of Medical Physics and Image Processing and Shandong Provincial Engineering and Technical Center of Light Manipulations, School of Physics and Electronics, Shandong Normal University, Jinan 250358, China
Received: 10 June 2020
ABSTRACT
Accepted: 30 August 2020
The protonation-controlled conductance switching of 4,40 -vinylenedipyridine (44VDP) molecular junctions was experimentally reported by Brooke et al. (Nano Lett 18(2): 1317–1322, 2018), where a change induced by protonation in the bonding at the molecule–metal interface was proposed as the key ingredient. Here, we perform a first-principles study on the spin-dependent transport properties of 44VDP molecular junctions modulated by protonation. The switching mechanism in the experiment is clarified; namely, the weak coupling strength at the molecule–metal interface is triggered by protonation of pyridyl groups in the 44VDP molecule. In particular, the protonation process modifies the organic–ferromagnetic spinterface, which reduces the number of hybrid interface states and causes an inversion of tunneling magnetoresistance from positive to negative values. Furthermore, a protonation-induced excellent spinfiltering effect is realized. This work sheds light on the mechanism of protonation at the organic–ferromagnetic interface and provides a promising way to realize multifunctional devices in organic spintronics.
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Introduction The perspective, ‘‘the interface is the device,’’ put forward by Herbert Kroemer has been widely acknowledged to be significant in the field of organic spintronics [1, 2]. Organic–ferromagnetic interface has therefore captured enormous attention in the past decade [3–5]. The reason is that the hybrid interface
states (HIS) can be generated from the orbital hybridization between organic molecules and ferromagnetic electrodes, which plays an important role in determining the spin injection efficiency and transport property [6–16]. The merits of the HIS in spin transport have been demonstrated by a host of theoretical and experimental studies [17–22]. For example, the HIS may constitute the intermediate step for the spin carriers between the Fermi level of the metal
Handling Editor: Kevin Jones.
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https://doi.org/10.1007/s10853-020-05213-1
J Mater Sci
electrode and the molecular conductive levels [23], which forms an additional platform to design the function of organic spintronic devices. The HIS depend on the interfacial contact details between the ferromagnetic electrode and the molecule, such as electrode geometry configuration [24, 25], absorption site [26, 27], and metal–molecule distance [28, 29], which are usually unstable and arduous to control in experiments. Hence, manipula
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