Low‐Energy, Ultrafast Spin Reorientation at Competing Hybrid Interfaces with Tunable Operating Temperature

Abstract

Abstract Information can be stored in magnetic materials by encoding with the direction of the magnetic moment. A figure of merit for these systems is the energy needed to rewrite the information by changing the magnetic moment. Organic molecules offer a playground to manipulate spin order, with metallo‐molecular interfaces being a promising direction for sustainable devices. Here, a spin reorientation transition is demonstrated in molecular interfaces of 3d ferromagnetic films due to a competition between a perpendicular magnetic anisotropy (PMA) induced by a heavy metal that dominates at high temperatures, and an in‐plane anisotropy generated by molecular coupling at low temperatures. The transition can be tuned around room temperature by varying the ferromagnet thickness (1.4 – 1.9 nm) or the choice of molecular overlayer, with the organic molecules being C 60 , hydrogen, and metal (Cu, Co) phthalocyanines. Near the transition temperature, the magnetisation easy axis can be switched with a small energy input, either electrically with a current density of 10 5   A   cm −2 , or optically by a fs laser pulse of fluence as low as 0.12  mJ   cm −2 , suggesting heat assisted technology applications. Magnetic dichroism measurements point toward a phase transition at the organic interface being responsible for the spin reorientation transition.