Ferromagnetic and Antiferromagnetic Coupling of Spin Molecular Interfaces with High Thermal Stability

TL;DR

This paper demonstrates room-temperature magnetic coupling in organic spin interfaces with graphene, showing how molecular orbital symmetry influences antiferromagnetic and ferromagnetic interactions with potential for spintronic applications.

Contribution

It reveals the mechanisms of magnetic coupling in organic interfaces mediated by graphene, highlighting the role of molecular orbital symmetry and superexchange interactions.

Findings

FePc couples antiferromagnetically with Co up to room temperature.

CuPc couples ferromagnetically with weaker and less stable coupling.

Superexchange interaction stabilizes the antiferromagnetic coupling.

Abstract

We report an advanced organic spin-interface architecture with magnetic remanence at room temperature, constituted by metal phthalocyanine molecules magnetically coupled with Co layer(s), mediated by graphene. Fe- and Cu-phthalocyanines assembled on graphene/Co have identical structural configurations, but FePc couples antiferromagnetically with Co up to room temperature, while CuPc couples ferromagnetically with weaker coupling and thermal stability, as deduced by element-selective X-ray magnetic circular dichroic signals. The robust antiferromagnetic coupling is stabilized by a superexchange interaction, driven by the out-of-plane molecular orbitals responsible of the magnetic ground state and electronically decoupled from the underlying metal via the graphene layer, as confirmed by ab initio theoretical predictions. These archetypal spin interfaces can be prototypes to demonstrate how antiferromagnetic and/or ferromagnetic coupling can be optimized by selecting the molecular orbital symmetry.