Department of Physics, University of Bath, Bath, BA2 7AY, United Kingdom.
School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom.
Sci Rep. 2017 Mar 24;7:45182. doi: 10.1038/srep45182.
High resolution scanning Hall probe microscopy has been used to directly visualise the superconducting vortex behavior in hybrid structures consisting of a square array of micrometer-sized Py ferromagnetic disks covered by a superconducting Nb thin film. At remanence the disks exist in almost fully flux-closed magnetic vortex states, but the observed cloverleaf-like stray fields indicate the presence of weak in-plane anisotropy. Micromagnetic simulations suggest that the most likely origin is an unintentional shape anisotropy. We have studied the pinning of added free superconducting vortices as a function of the magnetisation state of the disks, and identified a range of different phenomena arising from competing energy contributions. We have also observed clear differences in the pinning landscape when the superconductor and the ferromagnet are electron ically coupled or insulated by a thin dielectric layer, with an indication of non-trivial vortex-vortex interactions. We demonstrate a complete reconfiguration of the vortex pinning potential when the magnetisation of the disks evolves from the vortex-like state to an onion-like one under an in-plane magnetic field. Our results are in good qualitative agreement with theoretical predictions and could form the basis of novel superconducting devices based on reconfigurable vortex pinning sites.
高分辨率扫描霍尔探针显微镜已被用于直接可视化由覆盖超导铌薄膜的微米级 Py 铁磁体磁盘正方形阵列组成的混合结构中的超导涡旋行为。在剩磁状态下，磁盘几乎存在于完全磁通封闭的磁涡旋状态，但观察到的三叶草状杂散场表明存在弱面内各向异性。微磁模拟表明，最可能的起源是无意的形状各向异性。我们已经研究了添加的自由超导涡旋的钉扎作为磁盘磁化状态的函数，并确定了由于竞争能量贡献而产生的一系列不同现象。当超导体和铁磁体通过薄介电层电子耦合或隔离时，我们还观察到了在钉扎景观上的明显差异，表明存在非平凡的涡旋-涡旋相互作用。我们证明了当磁盘的磁化从涡旋状态演化到面内磁场下的洋葱状状态时，涡旋钉扎势的完全重构。我们的结果与理论预测非常吻合，并且可能成为基于可重构涡旋钉扎点的新型超导器件的基础。
