We present a detailed study on the static magnetic properties of individual permalloy nanotubes (NTs) with hexagonal cross-sections. Anisotropic magnetoresistance (AMR) measurements and scanning transmission X-ray microscopy (STXM) are used to investigate their magnetic ground states and its stability. We find that the magnetization in zero applied magnetic field is in a very stable vortex state. Its origin is attributed to a strong growth-induced anisotropy with easy axis perpendicular to the long axis of the tubes. AMR measurements of individual NTs in combination with micromagnetic simulations allow the determination of the magnitude of the growth-induced anisotropy for different types of NT coatings. We show that the strength of the anisotropy can be controlled by introducing a buffer layer underneath the magnetic layer. The magnetic ground states depend on the external magnetic field history and are directly imaged using STXM. Stable vortex domains can be introduced by external magnetic fields and can be erased by radio-frequency magnetic fields applied at the center of the tubes via a strip line antenna.

中文翻译：

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坡莫合金纳米管中稳定涡旋基态的起源和操纵

我们目前对具有六角形横截面的单个坡莫合金纳米管（NTs）的静态磁性能进行详细研究。各向异性磁阻（AMR）测量和扫描透射X射线显微镜（STXM）用于研究其磁基态及其稳定性。我们发现在零外加磁场中的磁化处于非常稳定的涡旋状态。它的起源归因于强烈的生长引起的各向异性，其易轴垂直于管的长轴。结合微磁模拟对单个NT进行AMR测量，可以确定不同类型的NT涂层的生长诱导各向异性大小。我们表明，可以通过在磁性层下面引入缓冲层来控制各向异性的强度。磁性基态取决于外部磁场历史，并使用STXM直接成像。稳定的涡旋磁畴可以由外部磁场引入，并且可以通过带状线天线通过施加在管中心的射频磁场来消除。