Unveiling the role of Fe 3 O 4 in polymer spin valve near Verwey transition
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jin Key Laboratory of Molecular Optoelectronic Sciences, Department of Chemistry, School of Sciences, Tianjin University, Tianjin 300072, China 2 Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparation Technology, School of Science, Tianjin University, Tianjin 300354, China 3 Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China 4 School of Physics and Electronics, Hunan University, Changsha 410082, China 5 Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China 6 Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou 350207, China © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 23 June 2020 / Revised: 3 September 2020 / Accepted: 3 September 2020
ABSTRACT The spinterface formed between ferromagnetic (FM) electrode and organic materials is vital for performance optimization in organic spin valve (OSV). Half-metallic Fe3O4 with drastic change in structure, conductivity and magnetic property near Verwey transition can serve as an intrinsic spinterface regulator. However, such modulating effect of Fe3O4 in OSV has not been comprehensively investigated, especially below the Verwey transition temperature (Tv). Here, we highlight the important role of Fe3O4 electrode in reliable-working and controllable Fe3O4/P3HT/Co polymer spin valves by investigating the magnetoresistance (MR) above and below Tv. In order to distinguish between different contributions to charge transport and related MR responses, the systematic electronic and magnetic characterizations were carried out in full temperature range. Particularly, the first-order metal-insulator transition in Fe3O4 has a dramatic effect on the MR enhancement of polymer spin valves at Tv. Moreover, both the conducting mode transformation and MR line shape modulation could be accomplished across Tv. This research renders unique scenario to multimodal storage by external thermodynamic parameters, and further reveals the importance of spin-dependent interfacial modification in polymer spin valves.
KEYWORDS polymer spin valves, Fe3O4, Verwey transition, magnetoresistance
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Introduction
Organic materials have attracted extensive attentions over the past few decades due to their unique nature of mechanical flexibility, low-cost, light weight, abundant photoelectrical properties, and chemical tailorability [1–8]. The utilization of organic semiconductors in spintronics owes significant advantage of extremely long intrinsic spin relaxation time (up to milliseconds) compared to the inorganic counterparts, which will preserve injected spin-polarized carriers and facilitate realistic spintronic applications [9, 10]. The report of the first vertical organic spin valve (OSV) in 2004 has triggered a huge amount of scientific inquiry [11, 12]. Recently, there has been a surge of interest in
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