Organic-inorganic hybrid spintronics

近年来，自旋电子学与有机材料的结合形成了有机自旋电子学的新领域。随着分子磁阻或有机磁阻效应的发现，以及有机自旋阀或自旋忆阻器等器件的发现，该领域的主要焦点是通过电极对分子的作用，在与有机分子接触的金属或铁磁引线组成的器件中诱导功能。这种作用包括在分子中诱导自旋极化，将分子磁矩与底物的磁矩固定或通过与底物的电子气体相互作用改变分子状态和轨道的效应。直到最近，我们才证明，反铁磁有序分子膜的作用也可以显著地揭示Co薄膜的交换偏倚。在这个项目中，我们打算扩大我们对分子在铁磁电极上的作用的研究，以实现多功能器件，其中分子的结构转变可以改变电极的磁性。本文将讨论两个主要观点。首先，可以通过电场、光或温度等外部刺激在磁性和非磁性状态之间切换的自旋交叉复合物将交换耦合到薄铁磁层上。通过改变分子的构象，从而改变它们的自旋状态，我们预计磁性衬底中的磁矩、磁各向异性和磁滞性会发生很大的变化。由于分子的两个自旋态之间的大尺寸变化，我们期望这种效应通过磁-弹性耦合得到增强。其次，利用铁电分子膜，利用铁磁体界面处的高电场诱导金属的磁性能发生变化，实现多铁杂化体系。这些系统将通过广泛的实验技术进行研究，从扫描隧道显微镜、原子和磁力显微镜等局部探针到x射线圆磁二色性、磁光克尔效应和输运测量等空间平均技术。通过结合两位主要研究者及其团队的专业知识，可以利用这种广泛的技术来确定这些混合系统中相关的物理相互作用。

The combination of spintronics and organic materials has recently led to the formation of the new field of organic spintronics. With the discoveries of effects like molecular magnetoresistance or organic magnetoresistance and devices like organic spin valves or spin-memristors, the main focus of the field was to induce a function in a device consisting of metallic or ferromagnetic leads in contact with organic molecules by the action of the electrodes on the molecules. This action includes effects inducing a spin-polarization in the molecules, pinning molecular magnetic moments to that of the substrate or modifying the molecular states and orbitals by the interaction with the electron gas of the substrates. Only recently, we demonstrated that also the opposite action can be of significantly size in revealing an exchange bias of thin Co films by the action of an antiferromagnetically ordered molecular film. In this project, we intend to expand our studies of the action of molecules on the ferromagnetic electrodes in order to realize multifunctional devices, in which structural transitions in molecules switch the magnetic properties of the electrodes. Two main ideas will be addressed. First, spin-crossover complexes that can be switched between a magnetic and a non-magnetic state by external stimuli like electric fields, light or temperature will be exchange coupled to thin ferromagnetic layers. By switching the conformation of the molecules and thus their spin state, we expect large changes in the magnetic moment, magnetic anisotropy and hysteresis in the magnetic substrate. We expect such effects to be enhanced by magneto- elastic coupling, thanks to the large size change between the two spin states of the molecules. Second, using ferroelectric molecular films, the high electric field at the interface to the ferromagnet can induce changes in the magnetic properties of the metal realizing a multiferroic hybrid system. The systems will be studied with a broad range of experimental techniques ranging from local probes like scanning tunnelling microscopy, atomic and magnetic force microscopy to spatially averaging techniques like X-ray circular magnetic dichroism, magneto-optical Kerr effect and transport measurements. By combining the know-how of the two principle investigators and their groups, this wide spectrum of techniques can be utilized to pinpoint the relevant physical interactions in these hybrid systems.