Electronic structure and exchange interactions in cobalt-phthalocyanine chains

Abstract

The magnetic properties and electronic structure of cobalt phthalocyanine (CoPc, spin-$\frac{1}{2}$) molecular chains have been studied using density functional theory with a hybrid exchange functional, over a wide range of chain geometries. Our theoretical results for the exchange interactions in the known phases $\ensuremath{\alpha}$-CoPc ($J/{k}_{B}\ensuremath{\sim}85$ K) and $\ensuremath{\beta}$-CoPc ($J/{k}_{B}\ensuremath{\sim}2$ K) are in quantitative agreement with recent magnetic measurements; we also find the computed exchange interaction agrees qualitatively with recent measurements by inelastic tunneling spectroscopy on thin films. The computed exchange interactions are much larger than those in copper phthalocyanine (CuPc), and are predicted to rise to a maximum of $J/{k}_{B}\ensuremath{\sim}400$ K when the molecules are face-on. The dominant exchange mechanism is expected to be superexchange arising from the direct hopping between ${d}_{{z}^{2}}$ orbitals.