Ferromagnetism in Ni quantum dots anchored graphdiyne

Achieving ferromagnetic ordering in two-dimensional carbon semiconductors like graphdiyne remains a challenge in spintronics. We synthesized Ni-doped graphdiyne (Ni-GDY) using an electrochemical method and found that adjusting the Ni atom concentration allows for a transition from paramagnetism to ferromagnetism, with a high Curie temperature of 175 K. Our density functional theory calculations revealed that the magnetic moment in Ni-GDY arises from Ni quantum dots. At low concentrations, the distant quantum dots result in paramagnetism, while at high concentrations, the formation of bound polarons and long-range exchange coupling through carbon p orbitals leads to ferromagnetism. This study clarifies the contradiction in magnetism observed in various transition metal-doped graphdiyne materials and highlights the potential applications of Ni-doped graphdiyne in electronic devices.