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Journal ArticleDOI

Oxygen Impurities Link Bistability and Magnetoresistance in Organic Spin Valves

07 Feb 2018-ACS Applied Materials & Interfaces (American Chemical Society)-Vol. 10, Iss: 9, pp 8132-8140
Topics: Organic semiconductor (55%), Bistability (55%), Magnetoresistance (55%), Spin valve (54%)

Summary (1 min read)

1. INTRODUCTION

  • The authors focus their attention to the prototypical bistable spin valve device composed of manganite and cobalt spin polarised injectors and a metal-quinoline transport layer.
  • By combining spectroscopic investigations and electrical characterization, the authors demonstrate that the application of a voltage bias causes oxygen migration within the organic spacer and the reversible modification of the molecule electronic configuration.
  • Experimental evidences link unequivocally the variable oxygen doping of the organic molecule with impurity driven conductivity effects.
  • The authors investigation provides a key element for the development of a picture of charge-spin effects in organic spintronic devices.

2. EXPERIMENTAL SECTION

  • Transmission electron microscopy (TEM) was employed for structural characterization, using a probe-corrected JEOL ARM200cF instrument that was operated at 200 kV and is equipped with a cold field emission electron gun and a Gatan Quantum electron energy loss spectrometer.
  • Impedance spectra were recorded with an Agilent E4980A LCR-Meter in the 20-100k Chemical investigation by Hard X-ray Photoelectron Spectroscopy and Xray Absorption Spectroscopy (XAS) was performed at room temperature on a sample holder that allows current voltage (I-V) characterization in a 2 point configuration directly within the analysis chamber.
  • 30 Spectra are acquired in total electron yield mode, by measuring the sample drain current, and they are normalized to the beam flux by using a clean gold sample as reference.
  • Surface cleanliness was checked by monitoring the surface-sensitive C and O XPS signals.

3. RESULTS AND DISCUSSION

  • Interestingly, among devices presenting reproducible MR in literature most of them have the LSMO oxide 13, 39, 76 as electrode or include the presence of oxide tunnel tunnel barrier 37, [77] [78] [79] indicating the oxide layers as most plausible sources of oxygens in such devices.
  • Recently Grünewald et al. 5 , discussing similar devices, advanced a model ascribing both the resistive 21 switching and magnetic characteristics uniquely to oxygen variations in the LSMO electrode.
  • 80 The authors set of data do not access the interfacial LSMO layer in reason of the limited electron escape depth for Hard X-Ray photoemission, providing little access to the deep buried interface with LSMO layer.
  • Nevertheless, their data provide a complementary interpretation of the mechanism, indicating significant modifications of the stoichiometry of the aluminum oxide barrier and substantial oxygen diffusion inside the organic layer, both factors controlling the device resistance.

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Citations
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Journal ArticleDOI
TL;DR: In this review, the recent advances of spin transport in π-conjugated molecular materials, considered as promising for spintronics development, have been highlighted, including molecular single crystal, cocrystal, solid solution as well as other highly ordered supramolecular structures.
Abstract: 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.

26 citations


Cites background from "Oxygen Impurities Link Bistability ..."

  • ...It is worth noting that, only with a high carrier concentration in the molecular layer, generally induced via the impurity band (Yu, 2014; Bergenti et al., 2018; Riminucci et al., 2019) or doped molecular semiconductors (Wang et al....

    [...]


Journal ArticleDOI
TL;DR: Basic knowledge of the fabrication and evaluation of organic spin devices is introduced, some remarkable applications for organic spin valves using molecular spacers are reviewed, and the current bottlenecks that hinder further enhancement for the performance of organicspin devices are discussed.
Abstract: 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.

16 citations


Cites background from "Oxygen Impurities Link Bistability ..."

  • ...The interface is known as the spinterface, where the organic molecular orbitals and the electronic energy levels of FM are hybridized [76,105,106]....

    [...]


Journal ArticleDOI
TL;DR: All salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration, and the critical importance of the carrier concentration in determining spin transport and MR in OSVs is highlighted.
Abstract: The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. Although carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of the charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical importance of the carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSV response.

14 citations



Journal ArticleDOI
Abstract: The need for new materials is constantly growing as their use becomes more and more critical for technological advances. Materials come in a wide variety of structures, dimensionalities, and phases...

8 citations


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Abstract: Many metal–insulator–metal systems show electrically induced resistive switching effects and have therefore been proposed as the basis for future non-volatile memories. They combine the advantages of Flash and DRAM (dynamic random access memories) while avoiding their drawbacks, and they might be highly scalable. Here we propose a coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms. The ion-migration effects are coupled to redox processes which cause the change in resistance. They are subdivided into cation-migration cells, based on the electrochemical growth and dissolution of metallic filaments, and anion-migration cells, typically realized with transition metal oxides as the insulator, in which electronically conducting paths of sub-oxides are formed and removed by local redox processes. From this insight, we take a brief look into molecular switching systems. Finally, we discuss chip architecture and scaling issues.

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26 Feb 2004-Nature
TL;DR: The injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure is reported, yielding low-temperature giant magnetoresistance effects as large as 40 per cent.
Abstract: A spin valve is a layered structure of magnetic and non-magnetic (spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field. The discoveries of giant magnetoresistance and tunnelling magnetoresistance in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics--'spintronics'. Intense research efforts are now devoted to extending these spin-dependent effects to semiconductor materials. But while there have been noteworthy advances in spin injection and detection using inorganic semiconductors, spin-valve devices with semiconducting spacers have not yet been demonstrated. pi-conjugated organic semiconductors may offer a promising alternative approach to semiconductor spintronics, by virtue of their relatively strong electron-phonon coupling and large spin coherence. Here we report the injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure, yielding low-temperature giant magnetoresistance effects as large as 40 per cent.

1,207 citations


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Abstract: Many organic electronic devices exhibit switching behavior, and have therefore been proposed as the basis for a nonvolatile memory (NVM) technology. This Review summarizes the materials that have been used in switching devices, and describes the variety of device behavior observed in their charge-voltage (capacitive) or current-voltage (resistive) response. A critical summary of the proposed charge-transport mechanisms for resistive switching is given, focusing particularly on the role of filamentary conduction and of deliberately introduced or accidental nanoparticles. The reported device parameters (on-off ratio, on-state current, switching time, retention time, cycling endurance, and rectification) are compared with those that would be necessary for a viable memory technology.

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Journal ArticleDOI
Abstract: Organic semiconductors are attractive candidates for spintronics applications because of their long spin lifetimes. But few studies have investigated how to optimize the injection of spin into these materials. A new study suggests that the metal/organic interface is key.

503 citations


Frequently Asked Questions (1)
Q1. What are the contributions in "Oxygen impurities link bistability and magnetoresistance in organic spin valves" ?

In this paper, the authors focus their attention to the prototypical device composed of metal-quinoline injectors with bistable sensors and demonstrate that resistive switching ( RS ) behavior in organic devices has excited substantial attention because, in addition to the well-known aspects of high performance and low volatility that are inherent to RS memory, the use of organic components would yield easy-to-process, flexible devices.