Atomic resolution determination of spin configuration at interfaces in functional materials in the transmission electron microscope

新的节能信息和通信技术对磁性材料的性能提出了越来越高的要求。为了应对这些挑战，材料的开发需要对其局部自旋构型的原子级知识，以便预测和控制其物理性质。在这个中德联合研究项目中，我们将开发功能材料界面自旋构型的原子尺度磁成像和光谱，以便对新型磁耦合现象的物理起源有一个基本的了解。我们的方法包括使用离轴电子全息（EH），电子磁性圆二色（EMCD），空间分辨电子能量损失光谱和色差校正的组合。特别是色差校正，有可能在原子水平上使用EH和EMCD来提高磁性表征的空间分辨率。这些技术的结合使用有望提供关于同一材料的面内和面外磁化的原子尺度信息，从而提供高空间分辨率的三维自旋信息。界面上的自旋、电荷、轨道和晶格自由度之间的协同相互作用将导致对交换弹簧磁体、铁磁和铁电材料界面上的磁电耦合、反铁磁和铁磁材料界面上的交换偏置以及磁性薄膜和衬底界面上的磁死层的原子水平实验理解。由于像差校正透射电子显微镜固有地提供了局部结构和组成信息，测量的自旋构型将与局部原子排列、应变分布、元素扩散、化学键、电荷转移、轨道耦合和原子水平的对称破缺相关。这种方法的结合将有助于在原子尺度上对磁性材料性质的物理起源有一个详细的基本理解，并将导致磁性材料的新设计，用于未来的应用，提高设备的功能。

New energy-efficient information and communications technologies place ever-increasing demands on the performance of magnetic materials. The development of materials to meet these challenges requires an atomic-level knowledge of their local spin configurations, in order to predict and control their physical properties. In this Joint Sino-German Research Project, we will develop atomic-scale magnetic imaging and spectroscopy of the spin configurations at interfaces in functional materials, in order to obtain a fundamental understanding about the physical origins of novel magnetic coupling phenomena. Our approach involves the use of a combination of off-axis electron holography (EH), electron magnetic circular dichroism (EMCD), spatially-resolved electron energy-loss spectroscopy and chromatic aberration correction. Chromatic aberration correction, in particular, has the potential to improve spatial resolution in magnetic characterisation using both EH and EMCD to the atomic level. The combined use of these techniques promises to provide atomic-scale information about both in-plane and out-of-plane magnetization in the same material, thereby offering three-dimensional spin information at the high spatial resolution. The cooperative interplay between spin, charge, orbital and lattice degrees of freedom at interfaces will results in an atomic level experimental understanding of exchange spring magnets, magnetoelectric coupling at interfaces between ferromagnetic and ferroelectric materials, exchange bias at interfaces between antiferromagnetic and ferromagnetic materials and magnetically dead layers at interfaces between magnetic thin films and substrates. Since aberration corrected transmission electron microscopy inherently provides access to local structural and compositional information, the measured spin configurations will be correlated with local atomic arrangements, strain distributions, elemental diffusion, chemical bonding, charge transfer, orbital coupling and symmetry breaking at the atomic level. This combination of methods will contribute to a detailed fundamental understanding of the physical origins of the properties of magnetic materials at the atomic scale and will lead to new designs of magnetic materials for future applications with improved device functionality.