Revealing the origin of magnetoresistance and resistive switching in organic spin valves

在2004年首次展示有机自旋阀（OSV）之后[1]，这些器件中的磁阻大多被解释为电子注入和自旋极化电子的检测，导致一种巨磁阻。然而，我们已经在许多实验中表明，至少在一些原型OSV中，磁阻不是源于通过有机材料中的电子态的传输[2]，而是源于导致隧穿磁阻（TMR）[3]和隧穿各向异性磁阻（TAMR）[4]的隧穿。此外，有机自旋阀中的电阻开关最近被报道[5]，因此除了磁阻特性之外还增加了新的功能。然而，详细优化这些效应所需的基础物理学从未得到充分理解。该项目的目标是通过研究TAMR、TMR的贡献及其相互作用，更好地理解导致OSV中磁电阻和电阻开关的物理学。与电阻开关。只有通过确定不同的贡献及其来源，才有可能最大限度地发挥每一种效果，并最终了解OSV是否或以何种方式用于应用。 自旋阀的哪一部分负责每种效应的发生和大小（单界面，双界面，体材料特性）？（二） 这种效果主要取决于其中一种材料还是仅仅取决于材料的组合？第三章 制造细节的作用是什么？界面准备对效果的外观是否至关重要？这些问题的答案可以通过仔细改变材料和材料组合以及所涉及的制造工艺来找到。通过我们小组在过去几年中进行的实验，已经开发出了用于调查这三种效应中每一种的原型装置和过程，这些装置和过程可以用作这些变化的起点。

After the first demonstration of an organic spin-valve (OSV) in 2004 [1] the magnetoresistance in these devices has mostly been interpreted as electrical injection and detection of spin polarized electrons leading to a kind of giant magnetoresistance. We have, however, shown in a number of experiments that at least in some prototypical OSV the magnetoresistance does not originate from transport through electronic states in the organic material [2] but rather from tunneling leading to tunneling magnetoresistance (TMR) [3] and tunneling anisotropic magnetoresistance (TAMR) [4]. In addition, resistive switching in organic spin valves has recently been reported [5] and thus added a new functionality besides the magnetoresistive properties. Nevertheless, the underlying physics which is necessary to optimize these effects in detail has never been sufficiently understood.The objectives of this project target a better understanding of the physics which lead to magnetoresistance and resistive switching in OSV by investigating the contributions of TAMR, TMR and their interplay with resistive switching. Only by identifying the different contributions and their origin will it be possible to maximize each of the effects and to finally understand whether or in what way OSV can be used for applications.To achieve this goal it is necessary to answer three questions:1) Which part of the spin valve is responsible for the occurrence and magnitude of each of the effects (single interface, both interfaces, bulk material properties)?2) Does the effect depend predominantly on one of the materials or merely on the material combination?3) What is the role of the fabrication details? Is the interface preparation crucial for the appearance of the effect(s)?The answers to these questions can be found by careful variation of the materials and material combinations as well as of the fabrication processes involved. With the experiments performed by our group over the last years, prototypical devices and processes for the investigation of each of the three effects have been developed which can be used as a starting point for these variations.