Abstract
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.
Highlights
It is well established that the probability of electrons passing through chiral molecules depends on the momentum of the charge and its spin
Layer and the tilt angle of the adsorbed molecules. This correlation links the selective adsorption of molecules with certain chirality on a perpendicularly magnetized substrate [5], and the magnetization reorientation caused by the self-assembled monolayer (SAM) adsorption process [4]
If the external magnetic field is perpendicular to the FM layer easy axis the tilt angle is unchanged; this may imply that the change in tilt angle continues after the adsorption event, when there is a magnetic relaxation of the magnetization towards the easy axis
Summary
It is well established that the probability of electrons passing through chiral molecules depends on the momentum of the charge and its spin. This effect has been named as the Chiral Induced. A relatively new aspect of this effect was recently discovered, and it is related with the interaction between chiral molecules and ferromagnetic substrate with perpendicular anisotropy. The first is magnetization reorientation of the ferromagnetic (FM) film where the molecules are adsorbed, even without any external magnetic or electric field [4].
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