Frustration on a centred pyrochlore lattice in metal-organic frameworks

TL;DR

This study reports a new highly frustrated magnetic material based on a metal-organic framework with a centred pyrochlore lattice, exhibiting spin liquid behavior and Coulomb physics signatures at very low temperatures.

Contribution

It introduces a novel metal-organic framework with a frustrated lattice structure that demonstrates classical spin liquid characteristics, expanding the experimental realization of such states.

Findings

Orders at 430 mK despite strong magnetic interactions

Displays features of a classical spin liquid in experiments

Structure factor reflects Coulomb physics with charges

Abstract

Geometric frustration inhibits magnetic systems from ordering, opening a window to unconventional phases of matter. The paradigmatic frustrated lattice in three dimensions to host a spin liquid is the pyrochlore, although there remain few experimental compounds thought to realize such a state. Here we go beyond the pyrochlore via molecular design in the metal-azolate framework [Mn(II)(ta)$_2$], which realizes a closely related centred pyrochlore lattice of Mn-spins with $S=5/2$. Despite a Curie-Weiss temperature of $-21$ K indicating the energy scale of magnetic interactions, [Mn(II)(ta)$_2$] orders at only 430 mK, putting it firmly in the category of highly frustrated magnets. Comparing magnetization and specific heat measurements to numerical results for a minimal Heisenberg model, we predict that this material displays distinct features of a classical spin liquid with a structure factor reflecting Coulomb physics in the presence of charges.