Investigation of the electronic and magnetic properties of Ni atoms in organometallic network

The molecular ligands are known to play vital roles in determining the magnetic property of transition metal atoms. Here by low temperature scanning tunneling microscopy and spectroscopy (STM/STS), we investigated the magnetic properties of Ni atoms coordinated to 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP) molecules on Au(111) substrate. In coordination networks, single Ni atoms and vertically arranged Ni atomic pairs can be accommodated among four adjacent TPyP molecules. The single Ni atoms show Kondo effect. The majority of the Ni pairs show no magnetic signal upon preparation, while the other two types show spin-flip excitations with zero field splitting energy of ~15.40 meV and ~2.67 meV, respectively. The non-magnetized Ni pairs upon preparation show spin-flip excitation in magnetic field. These experiments suggest that the two Ni atoms are antiferromagnetically coupled upon preparation, and can be switched to ferromagnetic coupling by magnetic field. Furthermore, the spatial distributions of the d-orbital of top Ni atom are revealed by STS mapping. Our work provides insights into how various magnetic properties can be realized in organometallic networks, and this coordination network may work as template for future study of magnetic property and magnetic interaction.