Antiferromagnetic Skyrmions in ultra-thin oxide films

反铁磁性Skyrmions是未来自旋电子应用的候选对象，因为它们结合了反铁磁体的优点，如磁场消失和快速动力学，以及类粒子Skirmions的独特性质。许多不同的材料表现出反铁磁相互作用，因此可能存在反铁磁天子。一些理论研究强调，与普通(铁磁)天空微子的偏转相反，这种反铁磁天微子有望沿着横向电流的方向精确地运动。虽然最近已经报道了合成反铁磁体中的Skyrmion，即反平行耦合的铁磁层中的Skyrmions，以及亚铁磁体中的Skyrmions，但尚未有实验证明反铁磁材料中存在单独的Skyrmion。孤立的反铁磁性Skyrmions总是亚稳天体。为了在反铁磁体中稳定这种局域扭曲的自旋织构，相关的磁相互作用之间的有利相互作用是必要的。与铁磁Skyrmions不同的是，它们的反铁磁对应物不能被外加磁场诱导，因此必须实现反铁磁态和亚稳态反铁磁Skyrmion之间的局域操纵。我们已经确定了超薄磁性氧化物薄膜的材料类别，在稳定和操纵反铁磁性Skyrmions方面都很有前途。根据制备条件的不同，可以将不同数量的氧加入到磁性薄膜的表层中，使得能够调节磁性，以实现对反铁磁性Skyrmions的稳定的有利的相互作用。许多超薄磁性氧化物薄膜是极性的，因此它们本质上放大了局部电场对自旋织构的影响，促进了对磁态的局部操纵。我们将在低温下使用自旋极化扫描隧道显微镜来表征模型类型超薄氧化物薄膜的磁序。这种实验方法特别适合于研究原子尺度的磁态，因为它结合了自旋灵敏度和原子分辨率。此外，探针尖端将被用来局部产生和湮灭具有垂直电流或电场的粒子状反铁磁天微子。

Antiferromagnetic skyrmions are promising candidates for future spintronic applications because they combine advantages of antiferromagnets, such as a vanishing magnetic strayfield and fast dynamics, with the unique properties of particle-like skyrmions. Many different materials exhibit antiferromagnetic interactions and thus may potentially host antiferromagnetic skyrmions. Several theoretical studies have highlighted that such antiferromagnetic skyrmions are expected to exhibit a motion exactly along the direction of lateral currents, in contrast to ordinary (ferromagnetic) skyrmions which are deflected. Whereas recently skyrmions in synthetic antiferromagnets, i.e. antiparallelly coupled ferromagnetic layers, and skyrmions within ferrimagnets have been reported, no experimental demonstration of an individual skyrmion in an antiferromagnetic material has yet been presented. Isolated antiferromagnetic skyrmions are always metastable objects. To stabilize such localized twisted spin textures in antiferromagnets, a favorable interplay between the relevant magnetic interactions is necessary. In contrast to ferromagnetic skyrmions their antiferromagnetic counterparts cannot be induced by external magnetic fields, thus a local manipulation between an antiferromagnetic state and the metastable antiferromagnetic skyrmion must be achieved.We have identified the material class of ultra-thin magnetic oxide films as promising for both the stabilization and the manipulation of antiferromagnetic skyrmions. Depending on the preparation conditions variable amounts of oxygen can be incorporated into the surface layers of a magnetic film, enabling a tuning of the magnetic properties in order to achieve a favorable interplay for the stabilization of antiferromagnetic skyrmions. Many ultra-thin magnetic oxide films are polar, and thus they intrinsically amplify the effect of local electric fields on the spin texture, facilitating the local manipulation of the magnetic state. We will use spin-polarized scanning tunneling microscopy at low temperatures to characterize the magnetic order of model-type ultra-thin oxide films. This experimental method is particularly suited to study atomic-scale magnetic states because it combines spin sensitivity with atomic resolution. Moreover, the probe tip will be used to locally create and annihilate particle-like antiferromagnetic skyrmions with vertical currents or electric fields.