Thickness-dependent spin bistable transitions in single-crystalline molecular 2D material

TL;DR

This study introduces a new class of 2D materials made of magnetic molecules, demonstrating thickness-dependent spin bistability and hysteresis, which could enable advanced control of magnetic functionalities in ultra-thin layers.

Contribution

It reports the synthesis and characterization of single-crystalline molecular monolayers with unique spin bistability properties, expanding the scope of 2D materials beyond traditional covalent structures.

Findings

Preservation of spin-crossover switching in few-layer molecules

Enhanced thermal hysteresis in thin molecular layers

Thickness-dependent spin bistability due to domain wall dynamics

Abstract

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.