Two-Dimensional VCl Nanoplates with Superparamagnetic Behavior over a Wide Temperature Range

Superparamagnetic materials are pivotal in high-density magnetic recording, magnetic sensors, and biomedical imaging. Here, we synthesize two-dimensional (2D) VCl nanoplates under ambient conditions by immersing reduced graphene oxide into an unsaturated VCl₃ solution. Transmission electron microscopy reveals a new 2D VCl structure with space group P4mm, which constitutes the first experimental realization of a monovalent vanadium compound. This unreported oxidation state of vanadium in the solid state represents a significant advance in transition-metal chemistry. Density functional theory calculations based on this structure predict a ferromagnetic ground state, indicating a novel 2D material with intrinsic magnetism. In the nanoplate form, long-range ferromagnetic order is suppressed, and the material exhibits superparamagnetism over a wide temperature range from 1.8 to 400 K. A saturation magnetic moment of 3.53 μB per vanadium ion is observed at 1.8 K, representing the highest magnetic moment per V ion and the lowest recorded temperature among reported superparamagnets.