Scanning Tunnelling Microscopy Study of Spin Interactions in Transition-Metal Phthalocyanine Adsorbates: Mechanisms, Signatures, and Control Strategies

Spin interactions between magnetic molecules and substrates are of fundamental importance, as they offer key insights into spin-related phenomena and underpin the development of energy-efficient spintronic devices. Transition-metal phthalocyanine (TMPc) molecules serve as exemplary model systems for probing these interactions, owing to their high structural stability, tunable magnetic moments, and well-defined local environment. When adsorbed on different substrates, TMPc molecules can exhibit a rich variety of spin-related phenomena including the Kondo effect, spin excitations, and Yu–Shiba–Rusinov (YSR) states, which can be directly resolved by scanning tunnelling microscopy (STM). This review summarizes recent STM advances on the coexistence and competition of spin-related phenomena in TMPc adsorbates, emphasizing the underlying mechanisms and practical control strategies enabled by chemical design and electric- and magnetic-field stimuli, and concludes with an outlook on emerging directions for future research.