The advent of two-dimensional (2D) crystals has led to numerous scientific breakthroughs. Conventional 2D systems have in-plane covalent bonds and a weak out-of-plane van-der-Waals bond. Here we report a new type of 2D material composed of discrete magnetic molecules, where anisotropic van-der-Waals interactions bond the molecules into a 2D packing. Through mechanical exfoliation, we can obtain single-crystalline molecular monolayers, which can be readily integrated into other 2D systems. Optical spectroscopy suggests the few-layered molecules preserve the temperature-induced spin-crossover switching observed in the bulk form but show a drastic increase in thermal hysteresis unique to these thin 2D molecule assemblies. The trapping of spin bistability with decreasing layer number can arise from domain wall dynamics in reduced dimensions. Our results establish molecular solids with strong anisotropy of intermolecular interactions as precursors to a novel class of 2D materials, affording new possibilities to control functionalities through substrate and interlayer interactions.
@article{arxiv.2203.10149,
title = {Thickness-dependent spin bistable transitions in single-crystalline molecular 2D material},
author = {John Koptur-Palenchar and Miguel Gakiya-Teruya and Duy Le and Jun Jiang and Rui Zhang and Xuanyuan Jiang and Hai-Ping Cheng and Talat S. Rahman and Michael Shatruk and Xiao-Xiao Zhang},
journal= {arXiv preprint arXiv:2203.10149},
year = {2022}
}