# Geometric Frustration on the Trillium Lattice in a Magnetic Metal-Organic Framework

Bulled, Johnathan M., Paddison, Joseph A. M., Wildes, Andrew, Lhotel, Elsa, Cassidy, Simon J., Pato-Doldán, Breogán, Gómez-Aguirre, L. Claudia, Saines, Paul J., Goodwin, Andrew L. (2022) Geometric Frustration on the Trillium Lattice in a Magnetic Metal-Organic Framework. Physical Review Letters, 128 (17). ISSN 0031-9007. (doi:10.1103/PhysRevLett.128.177201) (KAR id:94789)

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## Abstract

In the dense metal-organic framework Na[Mn(HCOO)3], Mn2+ ions (S = $$5\over2$$) occupy the nodes of a ‘trillium’ net. We show that the system is strongly magnetically frustrated: the Neel transition is suppressed well ´ below the characteristic magnetic interaction strength; short-range magnetic order persists far above the Neel ´ temperature; and the magnetic susceptibility exhibits a pseudo-plateau at $$1\over3$$-saturation magnetisation. A simple model of nearest-neighbour Heisenberg antiferromagnetic and dipolar interactions accounts quantitatively for all observations, including an unusual 2-k magnetic ground-state. We show that the relative strength of dipolar interactions is crucial to selecting this particular ground-state. Geometric frustration within the classical spin liquid regime gives rise to a large magnetocaloric response at low applied fields that is degraded in powder samples as a consequence of the anisotropy of dipolar interactions.

Item Type: Article 10.1103/PhysRevLett.128.177201 Q Science Divisions > Division of Natural Sciences > Chemistry and Forensics Paul Saines 27 Apr 2022 14:53 UTC 27 Apr 2022 15:40 UTC https://kar.kent.ac.uk/id/eprint/94789 (The current URI for this page, for reference purposes) https://orcid.org/0000-0002-4207-2112