Low-energy, ultrafast spin reorientation at competing hybrid interfaces with tunable operating temperature

TL;DR

This study demonstrates a tunable, low-energy, ultrafast spin reorientation transition at hybrid organic-metal interfaces, with potential applications in heat-assisted magnetic storage technologies.

Contribution

It reveals a controllable spin reorientation in molecular interfaces of ferromagnetic films driven by competing anisotropies, tunable near room temperature by material parameters.

Findings

Spin reorientation transition observed in molecular interfaces.

Switching of magnetization easy axis with low energy input.

Transition tunable by film thickness and molecular overlayer.

Abstract

Information can be stored in magnetic materials by encoding with the direction of the magnetic moment of elements. A figure of merit for these systems is the energy needed to change the information rewrite the storage 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, we demonstrate a spin reorientation transition in molecular interfaces of high magnetisation 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 to 1.9 nm) or the choice of molecular overlayer, with the organic molecules being C60, 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 per cm2, or optically by a fs laser pulse of fluence as low as 0.12 mJ per cm2, suggesting heat assisted technology applications. Magnetic dichroism measurements point toward a phase transition at the organic interface being responsible for the spin reorientation transition.