High Spin Cycles: Topping the Spin Record for a Single Molecule verging on Quantum Criticality

Theory predicts a number of interesting quantum critical phenomena for low-dimensional magnetic systems, where the ground state and thus low-temperature properties of a material change drastically upon even a small variation of an appropriate external parameter. Here we report a mixed 3d/4f cyclic coordination cluster, Gd₁₀Fe₁₀, that turns out to be very near or even at such a quantum critical point. The molecule forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbor Fe-Gd coupling and a frustrating next-nearest neighbor Fe-Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit a variety of frustration effects, among them giant magnetization jumps as well as macroscopic degeneracies of the ground state with profound caloric consequences. The present cluster is situated on the ferromagnetic side of the Quantum Critical Point with a ground state spin of S=60, which makes it simultaneously the magnetic molecule with the largest total spin ever observed for a magnetic molecule.
The present discovery is a lucky example where a magnetic material exists that corresponds to theory predictions. In addition, Gd₁₀Fe₁₀ constitutes a massive challenge for theory since the Hilbert space dimension assumes the staggering value of 2.7*10¹⁵.