Magnetoresistance and Spinterface of Organic Spin Valves Based on Diketopyrrolopyrrole Polymers

Abstract

recombination in organic light-emitting diodes and organic magnetoresistance (MR) devices. [9][10][11][12] Moreover, organic semiconductors have obvious advantages, lower cost, and better flexibility, and they have greater possibility in wearable and large area applications. [13][14][15][16][17][18][19][20] The most common prototype organic device using spin freedom is organic spin valves (OSVs), [5,11,[21][22][23][24][25] which consist of a nonmagnetic spacer sandwiched between two ferromagnetic (FM) electrodes, and based on the alignment of the electron spin relative to the FM layer magnetization orientation. In this research field, there are tunneling and diffusive regimes. [26] The tunneling regimes occur in relatively thinner spacers (<15 nm), and the mode is weakly dependent on temperature. The diffusive regimes are also called hoping in organic spintronics. This mode occurs in relatively thicker layers (≥15 nm), and it is strongly dependent on temperature. In addition, the present study lies in the diffusive regime owing of the conductivity mismatch problem and more abundant phenomena like Hanle effect in organic spintronics. For organic semiconductor, both spin-orbit interaction and the hyperfine interaction play very significant parts in determining the spin relaxation, but the origin of determining the spin relaxation in organic semiconductors is still unknown. Herein, OSV effect is characterized by the MR ratios, defined as MR = (R ap − R p )/R p , where R ap and R p denote the resistance in the antiparallel and parallel states of FM electrode magnetization direction, respectively. There are lots of efforts to explore organic spintronics Organic materials are proposed to be excellent spin transport layers due to their weak hyperfine and spin-orbit coupling interaction. Donor−acceptortype polymers PTDCNTVT-420 and PTDCNTVT-320 with diketopyrrolopyrrole (DPP) units are employed as the spacers in the organic spin valves, which have more advantages such as solution processing, higher mobility, and large area fabrication. The performance of polymers spin valves based on DPP units with different alkyl side chain lengths are studied. The different top ferromagnetic (FM) electrodes Co and Ni 80 Fe 20 are used for spin detection resulting in obvious distinct magnetoresistance (MR) values. The MR ratio of approaching 30% at 10 K is achieved with the Ni 80 Fe 20 electrodes using PTDCNTVT-420 with longer alkyl side chain lengths. Moreover, the MR behaviors are observed depending on various temperatures, which are related with the FM electrodes spin injection efficiency. The direct spinterface are also investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). In addition, the series of results indicate that the PTDCNTVT polymers can be used as good spin transport model materials and give clues for future polymers spintronic studies.

Electrical Transport in Polyaniline–Barium Ferrite Nanocomposites with Negative Giant Magnetoresistance

“…Compared with traditional inorganic semiconductor materials, because of the weak spin−orbit coupling and weak ultrafine interaction, 6 conductive polymer materials with advantages of simple manufacturing process, adjustable electrical conductivity, good flexibility, and low price play a pivotal role in the development of novel spin electronic devices. 7 Among them, the conductive polymer nanocomposites formed by combining polymer with different nanoparticles are employed in plenty of fields, involving electromagnetic interference shielding, 8 microwave absorption, 9 energy storage, 10 and electrocatalysis. 11 It is reported that there are two approaches to make the polymer nanocomposites possess the GMR effect.…”

“…Since the GMR effect was first discovered in the multilayered metal thin film structures in 1988, spin-electronic devices have been widely applied in computer memory, rotational speed sensors, biosensors, and so on. Compared with traditional inorganic semiconductor materials, because of the weak spin–orbit coupling and weak ultrafine interaction, conductive polymer materials with advantages of simple manufacturing process, adjustable electrical conductivity, good flexibility, and low price play a pivotal role in the development of novel spin electronic devices . Among them, the conductive polymer nanocomposites formed by combining polymer with different nanoparticles are employed in plenty of fields, involving electromagnetic interference shielding, microwave absorption, energy storage, and electrocatalysis .…”

Molecular and Interfacial Adjustment of Magnetoresistance in Organic Spin Valves Using Isoindigo-Based Polymers

“…23 In addition, the coupling between the conjugated polymers and the ferromagnetic (FM) electrodes in OSVs makes the interfaces of OSVs complex and thus determines the device performance at times. 26 Therefore, OSVs based on conjugated polymers have obtained normal positive magnetoresistance (MR) signals 21,22,24,27,28 as well as negative ones, 26,29,30 which also reveal the inner mechanism of spin transport and give rise to studies of the adjustment of MR Isoindigo (IID)-based conjugated polymers are a class of high-performance organic semiconductors (OSCs) with excellent field-effect and spin transport properties. 23 With the introduction of (E)-1,2-bis(3-cyanothiophene-2-yl)ethene, the lowest unoccupied molecular orbital (LUMO) energy levels of the IID-based conjugated polymers were lowered, which favors electron injection.…”

“…These materials have further expanded the boundaries of organic spintronics, where new physical concepts and functional devices are innovated. , As an important class of organic materials, conjugated polymers have been widely studied in organic electronics because of their characteristics of solution processing and flexibility . By these advantages, conjugated polymers exhibit enormous appeal in the aspects of flexibility of spin devices and optimization of spin transport. − Hence, conjugated polymers with different molecular structures have been utilized to study their spin transport properties, − with the aim of acquiring molecular engineering regularity of organic spintronics. Furthermore, process engineering has also been studied to realize the controllable and reproducible fabrication of polymeric spin valves …”

“…In addition, the coupling between the conjugated polymers and the ferromagnetic (FM) electrodes in OSVs makes the interfaces of OSVs complex and thus determines the device performance at times . Therefore, OSVs based on conjugated polymers have obtained normal positive magnetoresistance (MR) signals ,,,, as well as negative ones, ,, which also reveal the inner mechanism of spin transport and give rise to studies of the adjustment of MR signals. Nevertheless, most of the results stay at the targeted interpretation of the experimental phenomenon, where proactive initiation and adjustment of positive and negative MR are rare.…”