Isotropic helimagnets are known to host a diverse range of chiral magnetic states. In 2016, Rybakov et al., theorized the presence of a surface-pinned stacked spin spiral phase [F. N. Rybakov et al., New J. Phys. 18, 045002 (2016)], which has yet to be observed experimentally. The phase is characterized by surface spiral periods exceeding the host material's fundamental winding period $L_{\mathrm{D}}$. Here, we present experimental evidence for the observation of this state in lamellae of FeGe using resonant x-ray holographic imaging data and micromagnetic simulations. We find images of FeGe lamellae, exceeding a critical thickness of 300 nm ($4.3L_{\mathrm{D}}$), exhibit contrast modulations with a field-dependent periodicity of $\lambda \ge 1.4L_{\mathrm{D}}$, consistent with theoretical predictions of the stacked spiral state. The identification of this spiral state has significant implications for the stability of other coexisting spin textures, and will help complete our understanding of helimagnetic systems.

中文翻译：

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FeGe薄片中磁性表面螺旋的X射线全息成像

众所周知，各向同性螺旋磁体具有多种手性磁态。2016 年，Rybakov等人。，理论上存在表面钉扎堆叠自旋螺旋相[FN Rybakov et al。,新 J. 物理学。 18 , 045002 (2016)]，尚未通过实验观察到。该阶段的特征是表面螺旋周期超过主体材料的基本缠绕周期${\mathrm{大号}}_{\mathrm{D}}$. 在这里，我们提供了使用共振 X 射线全息成像数据和微磁模拟观察 FeGe 薄片中这种状态的实验证据。我们发现了 FeGe 薄片的图像，超过了 300 nm 的临界厚度（$4.3{\mathrm{大号}}_{\mathrm{D}}$），表现出对比度调制与场相关的周期性$\lambda \ge 1.4{\mathrm{大号}}_{\mathrm{D}}$，与堆叠螺旋状态的理论预测一致。这种螺旋状态的识别对其他共存自旋纹理的稳定性具有重要意义，并将有助于完成我们对螺旋磁系统的理解。