This work introduces a magnetic conductive atomic force microscopy (mc-AFM) measurement platform for determining spin polarizations, arising from the chiral-induced spin selectivity (CISS) effect along different directions in helical conducting fibers. By using the principle that the spin preference for electron transport in a chiral material changes with the momentum of the electron, this method quantifies the spin polarization of chiral materials, which straddle a ferromagnetic electrode, i.e., by taking measurements in regions to the right and left of the electrode while it is magnetized in-plane. The working mechanism of the measurement is shown using chiral polyaniline (PANI) fibers, and they reveal that the longitudinal, along the fiber's helical axis, and transverse, perpendicular to the fiber axis, magnetoresistance differ by about a factor of 2. The observations imply that the spin polarization in PANI fibers is not consistent with models that attribute the spin selectivity (or magnetoresistance) solely to the spinterface or to spin-dependent charge injection barriers. In aggregate, this new platform offers a simplified approach for extending the mc-AFM method to resolving the spin-filtered charge currents along different directions in oriented samples.

Keywords: chiral polyaniline fibers; chiral-induced spin selectivity; direction dependent CISS; magnetoresistance; spin polarization.

本文介绍了一种磁导性原子力显微镜（mc-AFM）测量平台，用于确定螺旋导电纤维沿不同方向的由手性诱导自旋选择性（CISS）效应产生的自旋极化。通过使用一种原理，即手性材料中电子传输的自旋偏好会随电子动量的变化而变化，该方法量化了跨越铁磁电极的手性材料的自旋极化，即在电极沿平面磁化时测量其左右区域的数据。利用手性聚苯胺（PANI）纤维的工作原理表明，沿着纤维螺旋轴纵向和垂直于纤维轴横向的磁阻相差大约两倍。观察结果表明，PANI纤维中的自旋极化与仅将自旋选择性或磁电阻归因于sp界面或自旋依赖电荷注入势垒的模型不一致。总体而言，这一新平台为扩展mc-AFM方法以解析沿定向样品不同方向筛选后的电荷电流提供了一种简化的方法。

关键词：手性聚苯胺纤维；手性诱导自旋选择性；方向依赖性CISS；磁阻；自旋极化。