A glass full of magnetism

Glasses are familiar materials, yet their atomic-scale organisation and physical properties remain difficult to fully understand. This challenge is particularly pronounced for magnetic glasses, where structural disorder strongly affects collective spin behaviour. Most conventional glasses are chemically simple inorganic systems, which limits their tunability and functionality. Metal–organic frameworks (MOFs) combine metal ions and organic linkers, and so by using organic chemistry to create different organic linker molecules, we have the ability to control the magnetic behaviour of MOFs.

In this paper we introduced a new route to prepare MOF glasses. This route avoids making any crystalline (ordered) MOFs as intermediates and avoids the formation of magnetic impurities. The purity of the glass enabled us to use neutron scattering experiments to probe its magnetic properties. Powder neutron diffraction experiments revealed , observed as diffuse magnetic scattering which indicate short-range antiferromagnetic (i.e. spins in opposite directions) correlations. These measurements together with measurements of how the size of the magnetic moment varies with temperature demonstrate antiferromagnetic interactions without the formation of an ordered magnetic state, consistent with a topologically disordered antiferromagnet.

This work was carried out in collaboration with the Instituto de Ciencia Molecular (Universidad de Valencia), the Centro de Ciências e Tecnologias Nucleares (Instituto Superior Técnico, Universidade de Lisboa) for Mössbauer spectroscopy, and the Institut Laue-Langevin for neutron diffraction experiments.