Tuning the quantum spin states of Co-phthalocyanine on good, semi-, and half-metals

Abstract

<p>Control of quantum spin states of magnetic molecules on surfaces has been actively pursued for emergent exotic physics and potential technological applications. Co-phthalocyanine (CoPc) is a prototypical molecular magnet with a spin of 1/2, which has been shown to be too fragile when the molecule is adsorbed on good metals but can be preserved on the semimetallic Sb(111) substrate. Here, we use first-principles calculations to reveal that, counterintuitively, the spin of individual CoPc is also quenched on the semimetallic Bi(111) substrate, and the underlying reason is attributed to a significant elevation of the Fermi level close to the Co-dz2 orbital by the stronger spin-orbit coupling in bismuth. We further show that the molecular spin can be recovered via intermolecular coupling, accompanied by a topological phase transition from a quantum spin Hall state to a magnetic topological semimetal. Finally, we demonstrate that the spin state of CoPc is enhanced on the half-metallic CrO2(110) substrate, associated with reverse band alignment and charge transfer. Collectively, our comparative studies establish rich tunability of molecular spins on different metal substrates for future molecular spintronic and quantum information devices.</p>