Correlation between Ferromagnetic Layer Easy Axis and the Tilt Angle of Self Assembled Chiral Molecules

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.

Charge and Spin Dynamics and Enantioselectivity in Chiral Molecules

“…In this context, an obvious question is how a spinpolarization can be generated and stabilized in a molecular structure which is in a closed shell configuration when isolated from the surrounding environment. Recent experiments demonstrate that a measurable spin-polarization can be obtained whenever chiral molecules are interfaced with metallic surfaces [42,[45][46][47]. Through the anomalous Hall effect, chiral molecules were, for instance, shown to control the magnetism in thin Co layers [42,45] and enantiomer separation on non-magnetic metals [46], whereas Yu-Shiba-Rusinov states [48][49][50] were observed in the vicinity of chiral molecules on the surface of superconducting NbSe 2 [47].…”

“…Recent experiments demonstrate that a measurable spin-polarization can be obtained whenever chiral molecules are interfaced with metallic surfaces [42,[45][46][47]. Through the anomalous Hall effect, chiral molecules were, for instance, shown to control the magnetism in thin Co layers [42,45] and enantiomer separation on non-magnetic metals [46], whereas Yu-Shiba-Rusinov states [48][49][50] were observed in the vicinity of chiral molecules on the surface of superconducting NbSe 2 [47]. Related to these observations are also the results showing strongly enantiomer dependent binding energies on ferromagnetic metals [51][52][53][54][55][56].…”

Charge Redistribution and Spin Polarization Driven by Correlation Induced Electron Exchange in Chiral Molecules

“…In this context, it is also natural to question whether the chiral molecules maintain their intrinsically spin-degenerate properties when attached to metals. Indeed, recent experiments suggest that a strong spin-polarization can be associated with the interface between chiral molecules and metallic surfaces [40,[42][43][44]. In Refs.…”

“…In the experimental observations of spin reversal using chiral molecules [40,42], the magnetization of a magnetized ferromagnetic layer, saturated in an out-of-plane configuration, was entirely switched. The simulations presented here, show a weaker anisotropy associated with the magnetic properties of the composite system.…”

Long-Timescale Magnetization Ordering Induced by an Adsorbed Chiral Monolayer on Ferromagnets

“…The same effect was demonstrated in many types of chiral molecules, including: double strand DNA; 1,3,4 Alpha-Helix or other types of protein that have both a helical structure and a chiral building block; [5][6][7] Helicene molecules that have only a helical geometry; 8 small chiral molecules such as amino acids with only one chiral center. 9 One of the most surprising phenomenon created by the CISS effect is the magnetization reorientation in a ferromagnetic layer with perpendicular anisotropy due to the chemical adsorption of chiral molecules of a given helicity on the thin film surface, 7,10 while non-chiral molecules did not produce this effect. While many theories have been developed to address the basic properties of the CISS effect, 11-15 the underlying physical mechanism driving this effect is still unclear.…”