Chemical design and magnetic ordering in thin layers of 2D MOFs

TL;DR

This study demonstrates the chemical design of stable 2D magnetic MOFs with tunable magnetic properties, novel layered topologies, and potential for magnetic detection in few-layer forms using nanomechanical resonators.

Contribution

It introduces new 2D MOF materials with rare layered topologies, tunable magnetic ordering, and applications in magnetic sensing at the nanoscale.

Findings

Layered MOFs can be chemically tuned for magnetic properties.

Novel 2D magnetic structures with rare topologies are created.

Thin layers of these MOFs can be used in nanomechanical magnetic sensors.

Abstract

Through rational chemical design, and thanks to the hybrid nature of metal-organic frameworks (MOFs), it is possible to prepare molecule-based 2D magnetic materials stable at ambient conditions. Here, we illustrate the versatility of this approach by changing both the metallic nodes and the ligands in a family of layered MOFs that allows the tuning of their magnetic properties. Specifically, the reaction of benzimidazole-type ligands with different metal centres (MII = Fe, Co, Mn, Zn) in a solvent-free synthesis produces a family of crystalline materials, denoted as MUV-1(M), which order antiferromagnetically with critical temperatures that depend on M. Furthermore, the incorporation of additional substituents in the ligand results in a novel system, denoted as MUV-8, formed by covalently bound magnetic double-layers interconnected by van der Waals interactions, a topology that is very rare in the field of 2D materials and unprecedented for 2D magnets. These layered materials are robust enough to be mechanically exfoliated down to a few layers with large lateral dimensions. Finally, the robustness and crystallinity of these layered MOFs allow the fabrication of nanomechanical resonators that can be used to detect -- through laser interferometry -- the magnetic order in thin layers of these 2D molecule-based antiferromagnets.