Ligand-mediated synthesis of freestanding room-temperature ferromagnetic CuCr 2 Te 4 nanosheets

Abstract

The synthesis of freestanding, room-temperature ferromagnetic two-dimensional (2D) materials from non-layered 3D lattices, where isotropic bonding resists anisotropic 2D growth, remains a fundamental challenge. Here, we address this by developing a ligand-mediated colloidal strategy to produce freestanding CuCr₂Te₄ nanosheets with controlled thickness and robust room-temperature ferromagnetism. Unlike substrate-dependent methods like chemical vapor deposition (CVD), our approach leverages facet-selective ligands to drive a Cu_1.43Te-to-CuCr₂Te₄ cation exchange pathway, enabling anisotropic growth of ultrathin nanosheets with preserved cubic close-packed order. Mechanistic studies reveal that oleyl alcohol stabilizes (111) facets during the transformation, suppressing strain and phase impurities (e.g., Cr₂Te₃) while ensuring ambient stability. Magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) measurements confirm a Curie temperature (T_C) above 300 K for thin nanosheets. Density functional theory (DFT) reveals that Cu doping enhances Cr-3d/Te-5p hybridization, leading to an increased spin-polarized density of states near the Fermi level, which in turn strengthens ferromagnetic exchange interactions. By decoupling synthesis from substrates and resolving growth pathways, this work establishes a scalable route to air-stable 2D magnets, advancing spintronic materials design with tunable anisotropy and thickness-dependent functionality.