Ligand-mediated phase engineering in magnetic ternary Cu-Cr-Se nanoplates

Phase engineering in the synthesis of nanocrystals (NCs) is fundamentally intriguing due to its ability to precisely synthesize NCs with distinct crystal phases. Ternary Cu-Cr-Se family of magnetic materials is known for their phase-dependent magnetic properties. However, phase diversity is also a double-edged sword that poses a significant challenge to the phase-selective synthesis of Cu-Cr-Se. In this study, we present the phase-controlled synthesis of Cu-Cr-Se two-dimensional (2D) nanoplates through ligand engineering. By integrating experimental observations with computational simulations, we demonstrate that the presence of trioctylphosphine (TOP) or oleylamine (OAm) ligands stabilize the Cu₂Se or CuSe (CuSe₂) intermediates, leading to the formation of CuCrSe₂ and CuCr₂Se₄ nanoplates, respectively. Furthermore, we reveal that the discrepancy between the room-temperature ferromagnetic CuCr₂Se₄ and antiferromagnetic CuCrSe₂ arises from the difference in the Cr orbitals coupling between two phases. Our work opens up a new strategy toward creating previously unprecedented nanostructures and exploring their phase-dependent applications.