The quantum origin of magnetic coupling in molecular crystals for spintronics

Organic-based magnetic materials have attracted significant attention in recent years, particularly in the domain of spintronics. However, in order to realize viable spintronic-based technologies, high temperature coupling is a necessity. Understanding the physical exchange mechanisms that underpin the observed ordering in magnetic materials provides an effective tool to engage with this issue. In this report, a decomposition methodology is adopted to analyze the coupling in two metal phthalocyanine systems-cobalt (II) phthalocyanine (CoPc) and copper (II) phthalocyanine (CuPc)-and to extract the contributing exchange interactions. A dimeric molecular geometry is used to approximate the periodic chain structure, and the exchange interactions between the two magnetic centers are examined. The results of the study offer a more comprehensive insight into the physical mechanism underlying the observed exchange interactions and reveal the relationship between the electronic configuration and emergent magnetic properties of each respective system. More specifically, the coupling in CoPc is shown to be attributable to a dominant kinetic exchange interaction arising from the single occupation of a dz2-derived a1g molecular orbital, while in CuPc, an indirect spin polarization mechanism is found to underpin the weak exchange interaction. This study, therefore, demonstrates the validity of applying the decomposition methodology to a dimeric system and highlights its importance as a powerful tool to investigate the physical nature of magnetic interactions in molecular magnets.