Classical spin liquid state in a rhombic lattice metal-organic framework

Discovering more and new geometrically frustrated systems remains an active point of inquiry in fundamental physics for the existence of unusual states of matter. Here, we report spin-liquid-like behavior in a two-dimensional (2D) rhombic lattice Fe-metal-organic framework (Fe-MOF) with frustrated antiferromagnetism. This Fe-MOF exhibits a high frustration factor f = |θ_CW|/T_N ≥ 315, and its long-range magnetic order is suppressed down to 180 mK. Detailed theoretical calculations demonstrate strong antiferromagnetic coupling between adjacent Fe³⁺ ions, indicating the potential of a classical spin-liquid-like behavior. Notably, a T-linear heat capacity parameter, γ, originating from electronic contributions and with magnetic field independence up to 8 T, can be observed in the specific heat capacity measurements at low-temperature, providing further proof for the spin-liquid-like behavior. This work highlights the potential of MOF materials in geometrically frustrated systems, and will promote the research of exotic quantum physics phenomena.