Ligand-induced magnetic changes in metal thin films

Abstract

We employ the planar Hall effect to sensitively probe the in-plane magnetization of a ferromagnetic thin film using a nearly perpendicular applied field. We establish that a significant change in coercivity occurs upon exposure to a wide variety of ligands, regardless of whether the film is capped with a diamagnetic overlayer or not. In the overlayer case, we believe that the change is due to a modified magnetic response of the diamagnetic capping metal. The size of the shift varies with ligand hardness, alkane chain length, magnetic sensor layer material, nonmagnetic overlayer material, and the thickness of each metal layer. The effect continues to be observable for thicknesses of at least 100 nm of Au deposited on 30 nm of Co. Au overlayers are shown to be more sensitive than Cu and Ag, both of which display shifts statistically indistinguishable from zero. Moreover, Au surfaces exposed to 1-dodecylthiol exhibit a larger effect than the same surface exposed to ethanol, the ligand with the greatest ligand strength examined. We demonstrate that the source of the effect is not magnetic contamination.