Applied Physics Department and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
Molecules. 2020 Dec 20;25(24):6036. doi: 10.3390/molecules25246036.
The spin-spin interactions between chiral molecules and ferromagnetic metals were found to be strongly affected by the chiral induced spin selectivity effect. Previous works unraveled two complementary phenomena: magnetization reorientation of ferromagnetic thin film upon adsorption of chiral molecules and different interaction rate of opposite enantiomers with a magnetic substrate. These phenomena were all observed when the easy axis of the ferromagnet was out of plane. In this work, the effects of the ferromagnetic easy axis direction, on both the chiral molecular monolayer tilt angle and the magnetization reorientation of the magnetic substrate, are studied using magnetic force microscopy. We have also studied the effect of an applied external magnetic field during the adsorption process. Our results show a clear correlation between the ferromagnetic layer easy axis direction and the tilt angle of the bonded molecules. This tilt angle was found to be larger for an in plane easy axis as compared to an out of plane easy axis. Adsorption under external magnetic field shows that magnetization reorientation occurs also after the adsorption event. These findings show that the interaction between chiral molecules and ferromagnetic layers stabilizes the magnetic reorientation, even after the adsorption, and strongly depends on the anisotropy of the magnetic substrate. This unique behavior is important for developing enantiomer separation techniques using magnetic substrates.
手性分子与铁磁金属之间的自旋-自旋相互作用强烈受到手性诱导自旋选择性效应的影响。之前的工作揭示了两种互补的现象：铁磁薄膜在外来手性分子吸附后磁化方向的重新取向，以及与磁性衬底相互作用的两种对映异构体的不同反应速率。这些现象都发生在铁磁体的易轴不在平面内的情况下。在这项工作中，使用磁力显微镜研究了铁磁体易轴方向对单层手性分子倾斜角和磁性衬底磁化方向重定向的影响。我们还研究了在吸附过程中施加外磁场的影响。我们的结果表明，铁磁层易轴方向与键合分子的倾斜角之间存在明显的相关性。与易轴在平面外的情况相比，易轴在平面内的情况导致的倾斜角更大。在外磁场下的吸附表明，磁化方向的重定向也发生在吸附事件之后。这些发现表明，手性分子与铁磁层之间的相互作用稳定了磁重定向，即使在吸附之后也是如此，并且强烈依赖于磁性衬底的各向异性。这种独特的行为对于开发使用磁性衬底的对映异构体分离技术非常重要。
