In the dense metal-organic framework Na[Mn(HCOO)3], Mn2+ ions (S=25) occupy the nodes of a `trillium' hyperkagome net. We show that this material exhibits a variety of behaviour characteristic of geometric frustration: the N\'eel transition is suppressed well below the characteristic magnetic interaction strength; short-range magnetic order persists far above the N\'eel temperature; and the magnetic susceptibility exhibits a pseudo-plateau at 31-saturation magnetisation. We demonstrate that a simple nearest-neighbour Heisenberg antiferromagnet model accounts quantitatively for each observation, and hence Na[Mn(HCOO)3] is the first experimental realisation of this model on the trillium net. We develop a mapping between this trillium model and that on the two-dimensional Shastry-Sutherland lattice, and demonstrate how both link geometric frustration within the classical spin liquid regime to a strong magnetocaloric response at low fields.
@article{arxiv.2012.10361,
title = {Geometric frustration on the trillium lattice in a magnetic metal-organic framework},
author = {Johnathan M. Bulled and Joseph A. M. Paddison and Andrew Wildes and Elsa Lhotel and Simon J. Cassidy and Breogan Pato-Doldan and L. Claudia Gomez-Aguirre and Paul J. Saines and Andrew L. Goodwin},
journal= {arXiv preprint arXiv:2012.10361},
year = {2022}
}